yournotes.org: ENMU - Ecology Notes

Ecology Notes: Lecture One

What is ecology?
- -the science of ecology examines the distribution and abundance of organisms, and the physical, and biological features of the environment that determine these distributions and abundances.
Hierarchy of Biological Phenomon
- -Molecules
- -Subcellular organelles
- -cells
- -tissue
- -organs
- -organ systems
- -#organisms
- -*populations
- -*communities
- -*ecosystems
- -#biosphere
- * The science of ecology deals primarily with these
- # These as well, but to a lesser extent
- -Complexity increases as we move from molecules to biospheres
Levels of Science
- -Description
- -Correlation (doesn't reach cause and effect)
- -Experiments (manipulation)
- -Synthesis
The Science of Ecology seeks to:
- -Explain and Understand
- -Predict
- -Conserve
- -Exploit
It is important to realize that there are two classes of explanation in biology
- -Proximate Causation
  - -a fish lives in a particular stream because it has a pH it prefers
  - -a polar bear eat a seal because it tasted good
  - -animals mate because it feels good
  - -these are immediate reasons
- -Ultimate Causation
  - -the present distribution of our fish reflects the ecological experiences of its ancestors (i.e. they were more successful in streams with this pH)
  - -the bear is a more efficient feeder by perfering food high in triglycerides (fat)
  - -animals that mate pass on their genes
  - -evolutionary reasons
- -Proximate and Ultimate causation are "two sides of the same coin"
Organims appear to match their environment
- -through adaptation
- -what is adaptation
  - -variation in the population
  - -some of the variation is heritable
  - -Different individuals leave different #'s of descendants
    - -due to differential rates of survival
    - -due to differential rates of mating (reproduction)
      - -sexual selection
  - -number of descendants depends on the characteristics of the individual and the environment
    - -i.e. color of individual being attractive to both females/males and predators
    - -i.e. it is the interaction
      - -the characteristics of the environment play a very large role in selecting the characteristics of the individual
Stabilizing selection selects against mutations and counters evolution
- -Do Species reach prefection?
  - -No: the environment is always changing
- -The evolutionary process is not directed (ie mutation is random) with regard to environmental change
- -part of the distribution leaves relatively more offspring than other parts of the distribution
  - -these individuals have the greatest fitness
- -factors other than fitness are also important in the distribution and abundance of organisms
- -Movement of land masses
  - -some organisms live where they do because of the movement of the continents
    - -ie distribution changes due to plate tectonices
  - -first proposed by biologist due to distributions that could not be explained by dispersal (eg ratite birds of the world, large flightless birds ie. ostrich, emu, etc)
- -Historical changes in climate, or land formation, can also cause distributional patterns
  - -they may leave refugia where organisms once lived continously
    - -eg. nunataks: "islands" in a sea of glacier
    - -kipukas: "islands" in a sea of lava
    - -these leave refugia where an organism may survive
    - -refugia may be quite distant an organism once lived continously
  - -disperal combined with isolation leads to speciation
    - e.g. Picture wing Drosphila of Hawaii
      - -about 500 species that are endemic to Hawaiian Islands
      - -endemic: found nowhere else on earth
Potential Differences in River Systems
- -water chemistry eg pH
- -volume eg velocity
- -substrate eg. type/intutices
- -community structure eg. vegetation, primary consumers, secondary consumers, predators
Prezygotic isolation:
Postzygotic isolation:
- -represents about 1/3 of the World's species
- -populations are isolated by islands and on kipukas
  - -if gene flow between islands or kipukas is less than the rate of divergence (ie. change in gene frequencies due to selection/drift) speciation may occur
- -sometimes species are distributed where they are because they evolve there
- -we do find convergent evolution in response to ecological circumstance
  - -eg. sometimes a certain morphology is found because it is the most efficient
  - e.g. fusiform body shapes in aquatic environments
- sometimes convergence can lead to parallel evolution
  - e.g. marsupial mammals primarily radiated in Australia
  - Although quite different from placental mammals they show a striking similarity in form and function
- an ecological niche is the relationship between an organism and the environment
  - i.e. it defines where an organism can live
  - the resulting ecological niche is an n-dimensional hypervolume
- similiar morphology is not always due to convergent evolution
  - e.g. megaphytes (rosette treelets)
    - all have large leaves
    - large flowers
    - truncks appear large due to layering of dead leaves
    - pliotrophy
- -alternately, organisms that appear quite differently morphologically may be similiar ecologically
  - -eg. Kangaroo and sheep
    - -exploit the same class of environmental resources in a similar way
    - -they are however very different physically
    - -under this situation, the organisms are said to belong to the same ecological guild
Particular types of organism usually characterize particular ecological situations
- -Biomes: are the broadly defined major catagories of the world's plant assemblges
  - -Tundra: consists largely of lichens (fungus/algal symbionts) mosses and dwarf trees
    - -permafrost
    - -liquid water only available for short periods
    - -arctic and subarctic regions
    - -same conditions occur at high elevation
      - -alpine tundra
  - -Northern Coniferous Forest (Taiga)
    - -mostly evergreen conifers
    - -no liquid water much of the year
    - -broad belts across North America and Eurasia
  - -Temperate Forest
    - -mixed conifer and broadleaf forest
    - -usually moist, dripping conditions, but periods when liquid water is in short supply
    - -much of North America and North Central Europe fall under this biome
  - -Grassland
    - -temperate grassland (aka praire, steppe, pampas, veld)
    - -tropical grassland (aka savannah)
    - -primarily grass vegetation
    - -periodic drought
    - -community strucutre largely determined by grazers
    - -much of North America, South America, and Africa
  - -Chaparral
    - -occurs in Mediterranean-like climates
    - -dominant plants are scrubs
    - -drought is common (less rain than grasslands)
    - -Mediterranean, coastal California, Coastal Chile, Coastal South Africa
  - -Deserts
    - -Hot Deserts
      - -cactus (eg. Mojave, Sahara)
    - -Cold Deserts
      - -usually high deserts
      - -sage, Juniper/Pinion
      - -eg. Gobi Desert, Eastern 1/3 of Oregon
    - -less than 25cm of rain annually
  - -Tropical Rainforest
    - -greater than 200cm of rain per year
    - -richest species composition in the world
    - -typically between the tropics of Cancer and Capricorn
  - -Other, nonterrestrial biomes exist
    - -Marine
      - -Kelp Forest, Coral Reef, Rock Reef, Sand Flats
    - -Freshwater
      - -pool, riffles, lake zones
    - -Underwater Biomes
  - -There are convergences between communities
  - -despite the concept of biomes, there are no truly homogenous environments in nature
    - -results in different characteristics for different environments
      - -leads to different selection pressure
        -leads to diversity among communities
  - -also most environments have gradients of resources or conditions
    - -leads to different selection pressure
      - -leads to diversity among communities
  - -the very pressure of some species within the "same" environment will change the environment
    - -eg. african elephant, praire dog (keystone species)
Keystone species: a species whose activity largely determines community structure
- -eg. African elephant, praire dogs: both are diggers and provide new habitat for animals
Coexisting species are usually different
- -often the differences are subtle
- -each matches the environment
  - -may restrict certain activity to a certain part of the environment
  - -eg. feeding positions and activity of warblers in the NE US
    - -show habitat or resource partitioning
Sympatry: a species or population live in the same place
Allopatry: a species or population live in different places
Such patterns raise questions that aer of a general nature of ecology
Habitat or resource partitioning is most intense when the species or populations are sympatric or show the greatest sympatry
- -Must coexisting species be different?
  - -if so, how different?
  - -species can overlap, but not in all dimensions
  - -if they overlap in all dimensions, they are the same species
- -are simularities and differences due to present or past interactions
What about competition within a species
- -even with ample gene flow, locally favored genotypes may have such an advantage that less favorable combinations are eliminated
- -this leads to the formation of ecotypes
  - -which are local matches between organisms and their environment within a species
    - -ie. genetic variaties within a species
      - -eg. herb yarrow
        -Achillea lamulosa: increase in elevation brings decreased height, but all the individuals are from the same species
Selectively relevant variation within a species goes to a smaller scale than an ecotype
- -there is often variation within small local populations
  - -in recongizable forms
- -this variation is called polymorphism
  - -rare mutants do not count
  - -must be two or more forms that are maintained by population dynamics
- -polymorphism involes two or more forms that are maintained by population dynamics
  - -not simply mutation or immigration
- -Variation in the environment
  - -gradient
    - -at one end of suitable habitat one form is favored, yet the other form is favored at the other end
  - -habitat appears as a mosaic or patchwork
    - -a different patch may favor a different morph
    - -eg. sometimes an organism is the environment
      - -Panites compressa: finger coral
        -makes a mosaic in which animals live
  - -differential success of genotypes within the mosaic may lead to polymorphism
- -Heterozygotes have greater fitness
  - -homozygotes are maintained due to mendelian genetics
    - -eg. sickle cell anemia
      - -heterozygotes suffer little from malaria
      - -homozygotes are dangerously anemic or susceptible to malaria
- -Frequency dependant selection
  - -each morph does well when it is rare
    - -often occurs in insects that are taken by vertebrate predators
      - -eg. birds and pepper moths
    - -predators may form search images
    - -the uncommon morph may have a higher probability of survival than the common morph
  - -when alternative mating strategies have equal lifetime fitness
    - -territorial male blue gill sunfish, sneakers and female mimikes of the sunfish
    - -sneaker: sneaks in and drops load of sperm and takes off
Co-evolutionary processes
- -strongest matches between organisms and environment
  - -"environment" is often another species
- -co-evolution is defined as reciprocal
  - -organism A gene frequences(traits) alter due to the interaction with organism B
  - -organism B gene frequences are then altered due to the alteration of the gene frequences in organism A
- -"tit for tat" evolution
  - -difficult to demonstrate
  - -"species pairs" are often described
  - -eg. milkweed and monarch butterflies
  - -eg. yucca and yucca moths
  - -now called "diffuse co-evolution" because the species pairs did not evovle in a vacuum
Factors Limiting distributions
Species is absent because:
- -Disperal >> survive >> inaccessable
  - -no: survival >> behavoir >> yes >> habitat selection
    - -no: behavior >> other species >> yes >> predators, parasites, competition
      - -no: other species >> physical environment >> yes >> resources
        -no/yes: physical environment >> conditions
many organisms do not occupy their potential range
- -if transplanted, they survive, reproduce, and spread
  - -eg. European starling
    - -spread over the US and Canada in about 60 years time
    - -80 birds were released in Central Park, NY in 1890
    - -80 more in 1891
American chestnut
chinese chestnut brought the chestnut blight
limited by disperal to use of habitat, but from 1934 to 1953 the number of american chestnuts
declined dramaticlly
Dispersal limitation (local scale)
- -freshwater organisms are often influenced by dispersal
  - -Boycott- early studies on dispersal using aquatic snails(distribution) in England
    - -in one study he found 150 ponds, 84 of which were cut-off (isolated)
      - -all lacked two common snails
        -Plamorbis corneus
        -Bithinia tentacuta
      - -Boycott transplanted 14 of each and found that only 10 suvived from the corneus and none survived form the tentacuta
Why disperse?
- -escape competitors
- -utilize newly avaible habitat
- -escape predators (parasites, etc)
- -escape imbreeding depression (build-up of bad genes) and outbreeding depression
The general argument is that an organism should disperse if the possiblity of reaching an advantagous site exceeds the probability of death or reaching a disadvantagous site.
- -Dispersal has been described as an ESS (Evolutionary Stable Stragedy)
  - -ie. a stradegy that cannot be invaded by an alternative stragedy
- -most dispersing individuals die (never reach advantagous habitat)
- -what options do organisms have
  - -stay at home (do not disperse)
    - -matter of scale
    - -very rare
  - -devote entire life to dispersal strategy
    - -eg. fugitive species: are organisms which grow or colonize predomantly disturbed habitat (weeds)
  - -dispersal polymorphism
    - -a somatic polymorphism
      - -or a behavioral polymorphism
    - -"bet hedging" in dispersal
      - -some morphs are made for dispersal, others are not
    - -the bet is hedged in that at least some offspring will be successful in an unpredictable environment
- -a dispersal strategy is costly
  - -probability of mortality is high
  - -specialization for dispersal involves sacriface of tissue and energy
    - -eg. an energy budget; growth, reproduction, maintaince
- -dispersal has been difficult for ecologist to study
  - -studing dispersal requires known individuals and the ability to track them
  - -dispersal has often been neglected in demographic studies
    - -ie. studies of changes in population size through birth rates, mortality, migration, etc.
  - -dispersal was accounted for in a study of demographic processess of a bird (great tit) in England
    - -the bird had been previously described as having a low rate of dispersal
    - -yet when looked at closely 57% of the breeding population were immigrants to the local population
Temporal Dispersal
- -dispersal in time
- -instead of natural selection working on where to be metabolically active, here we have a case of natural selection works on when to be metabolically active
- -animals and plants, often seeds, go through periods of dormancy
  - -dormancy can be predictive
    - -ie. in response to a cue indicating harsh times ahead
      - -common cues are cold temp, photoperiod, etc.
  - -dormancy can be consequential
    - -in direct response to a harsh stimulus
      - -eg. temp
- -predictive dormancy in insects is called diapause
  - -eg. many grasshoppers have an obligatory diapause in their egg stage
    - -development is arrested
    - -eggs require a long cold period before development starts again
- -the "periods" of cold is not in units of chronological time, but instead measured in "physiological time"
- -once temp. is above a threshold development takes place
  - -eg. Grasshopper Austroicefes aruciala
    - -a threshold of 16C above which there is a linear relationship between growth and temp.
    - -physiological time is measured in "day-degrees above threshold"
    - -Time to hatching for A. cruerata is 70 day degrees above threshold
      - -eg. time(d) x temperature above threshold(C) = day degrees
      - -At 20C how long would it take our grasshopper to hatch
        - days = day degrees divided by temp above threshold
        - days = 70 day degrees / 4 degrees above threshold
        - days = 17.5 days
  - -sometimes diapause is facultative
    - -it is cued by environmental conditions, yet only occurs under certain environmental conditions or contexts
    - -eg. Drosphila obscrum: fruit flies
      - -four generations per year in England
      - -photoperiod cues only one generation
        -results in diapause over winter
An insect has a threshold of 20C. How many degrees above the threshold will be required if the insect needs 45.5 day degrees and hatched in 7 days.
- - 7 days multiplied by n = 45.5
- - n = 6.5C
Consequential Dormancy
- -eg. hibernation in mammals
  - - in direct response to adverse conditions
- -eg. enfored dormancy in plants
  - -for seeds
  - -stay dormant in an absence of appropriate conditions
    - -eg. water, temp, etc
- -another type of dormancy in plants is innate dormancy
  - -predictive
  - -most flowering plants
    - -drop dormant seed
      - -only germinates after special external stimulus
        -eg. low temp, photoperiod
  - -innate dormancy is predictive
    - -eg. after some low maximum temp
      - -indicates good times ahead
  - -synchronizes germination
  - -competition
- -organisms disperse into habitats into which they can
  - -survive
  - -grow
  - -reproduce
- -where an organism has been able to persist (usually refers to ability to reproduce) has been referred to as its ecological niche
  - -n-dimensional hypervolume
    - -the n-dimensional hypervolume is the fundamental niche of the organism
    - -a realized niche refers to the more limited spectrum of variables (conditions, resources, etc.) that allow it to persist in an area
Population Parameter(measurement)
- -organisms occur in varing density
  - -eg. cactus are common in the desert, but rare elsewhere
  - -to make statements such as this precise, we need to quantify our findings
  - -the "population" is often the unit of study
    - -defined: a group of organisms of the same species occupying a particular space at a particular time(Vereb 1978)
      - -eg. the population of leopard seals in Antarctica
      - -biologically vague
        -boundaries in space and time often are set by biologists
        -usually for the purposes of estimation of size or density of the population
- -for management purposes biologists are most often interested in demes
  - -a deme is a local population of interbreeding individuals
- -the primary characteristic of a population in which biologists are interested is its size or density
- -four processes are important in the determination of population size or density
Measurement of population size or density
- -density is numbers per unit area or volume
- -techniques for measurement will vary with the population study
  - -due to size and mobility of the organisms
Techniques of measurement of absolute population density
- 1) Total Counts
  - -most direct way
  - -best example - human census data
  - -other examples
    - -counts of singing males in breeding areas for birds
    - -seal breeding populations
- 2) Sampling methods
  - A) Use of quadrats (not quadrants!)
    - -a quadrat is a sampling area of any shape or size
      - -Note: term is also used for the device used to sample the area
    - -quadrat samples are randomly taken in a given study area
    - -all individuals are counted in each quadrat
    - -results are extrapolated to the entire area
      - -eg. we randomly sample 10 1/100 m^2 quadrats
      - -an average of 19 beetles per quadrat is found
      - -Beetle per m^2: 1900 beetles per m^2
    - -a special type of quadrat is a transect line
      - -often used over large areas
        -eg. measuring tape over a coral reef
    - -these methods assume:
      - -population of each sampled quadrat is exactly known
      - -area of each quadrat is known and the same
      - -quadrats are representative of the whole area (or time)
        -random sampling
        -large sample area
  - B) Mark-recapture methods
    - -Techniques of capture, marking, release, and recapture
      - -a primary method in animal ecology
    - -to find population size we need to know just two things
      - -Number of marked animals alive (M, where M=marked animals)
      - -the proportion of the total population that is marked (M/M+U where U=unmarked animls)
      - -proportion of the total population that is marked is estimated by awing a random sample
        -assumes that the probability of taking marked and marked animals is equal
      - - if the sample is random, the number of marked animals in the sample/ divided by the total number caught in the sample is the same proportion of the number of marked animals in the population divided by the total population size
    - -Example:
      - Population estimation by the Peterson method;
      - -The estimator for the Peterson method is N^ (^=estimated value) which equals MC/R = N^ (estimated population size)
        M = (number of individuals marked and released)
        C = (second capture sample size includes both marked and unmarked individuals)
        R = (recapture sample, ie. the number of individuals in the second sample that are marked)
      - -variance of the estimator is given by S^2 = N^^2
        N^^2[(N^-M)(N^-C)]/(MC(N^-1))
      - -there are only two sampling periods in the Peterson method
        -Time 1: Capture, mark, and release
        -Time 2: capture, check for marks
        -Time interval between sampling periods varies, but must be relatively short
        -this method assumes no recruitment of new animals into the population between samples
  - Example of the Peterson method for population size estimation
    - -technique used with mobile species
    - -eg. catch and mark 127 bluegill sunfish
      - - mark and release them
      - -a week later catch 150 individuals and 29 are marked
      - -M = 127 bluegill sunfish
      - -C = 150 bluegill sunfish
      - -R = 29 bluegill sunfish
      - -N^ = MC/R = (127 x 150)/29 = 657 bluegill sunfish
      - -S^2 = N^^2 (N^-M)(N^-C)/MC(N^-1)= 657^2 =
        -657^ (657-127)(657-150)/ [127x150(657-1)] = 9281.4483
      - -s = square root of 9281.4483 = 96.3403
      - -thus the estimate for the population is N^ = 657 +/- 96SD bluegill fish
      - -N^ +/- 1.96(SD) = 95% CI
      - -N^ = 657 +/- 1.96(96) = 657 +/- 188
      - -P( 469 < N^ < 845 ) = .95 CI
    - -this estimator is biased for small sample sizes
      - -estimates are less than true population size
    - -bias is negligible when the sample is large such that MxC > 4N^
      - - 127 x 150 > 4 x 657
      - - 19050 >> 2628
  - There are a few assumptions using the Peterson method
    - -marked and unmarked animals are captured randomly
      - -ie. they have an equal probability of capture
      - -some animals get trap "happy" or shy
        -ie. they behave toward gear differentially
    - -marked and unmarked animals suffer the same mortality
      - -tags often cause injury and infection
        -may attract predators
      - -also violates the assumption if the marks render protection
    - -marks are not lost or overlooked
      - -tags often fall off
      - -mutilation tags often grow back
      - -human error in examining animals for tags
    - -under certain circumstances it is possible to test the randomness assumption
      - -eg. observations of behavior
    - -reliability of propulation size estimates are determined with standard statistical methods
Measurements of relative density
- -these estimates represent some relatively constant, but unknown, relationship to total population size
- -note: all of the relative estimators should be viewed skeptically until the assumed relationship with density is studied

Lecture Two

Population estimation by the Peterson method;
- -The estimator for the Peterson method is N^ (^=estimated value) which equals MC/R = N^ (estimated population size)
  - M (number of individuals marked and released)
  - C (second capture sample size includes both marked and unmarked individuals)
  - R (recapture sample, ie. the number of individuals in the second sample that are marked)
- -variance of the estimator is given by S^2 = N^^2
  - N^^2[(N^-M)(N^-C)]/(MC(N^-1))
- -there are only two sampling periods in the Peterson method
  - -Time 1: Capture, mark, and release
  - -Time 2: capture, check for marks
  - -Time interval between sampling periods varies, but must be relatively short
    - -this method assumes no recruitment of new animals into the population between samples
Example of the Peterson method for population size estimation
- -technique used with mobile species
- -eg. catch and mark 127 bluegill sunfish
  - - mark and release them
  - -a week later catch 150 individuals and 29 are marked
  - -M = 127 bluegill sunfish
  - -C = 150 bluegill sunfish
  - -R = 29 bluegill sunfish
  - -N^ = MC/R = (127 x 150)/29 = 657 bluegill sunfish
  - -S^2 = N^^2 (N^-M)(N^-C)/MC(N^-1)= 657^2 =
    - -657^ (657-127)(657-150)/ [127x150(657-1)] = 9281.4483
  - -s = square root of 9281.4483 = 96.3403
  - -thus the estimate for the population is N^ = 657 +/- 96SD bluegill fish
  - -N^ +/- 1.96(SD) = 95% CI
  - -N^ = 657 +/- 1.96(96) = 657 +/- 188
  - -P( 469 < N^ < 845 ) = .95 CI
- -this estimator is biased for small sample sizes
  - -estimates are less than true population size
- -bias is negligible when the sample is large such that MxC > 4N^
  - - 127 x 150 > 4 x 657
  - - 19050 >> 2628
There are a few assumptions using the Peterson method
- -marked and unmarked animals are captured randomly
  - -ie. they have an equal probability of capture
  - -some animals get trap "happy" or shy
    - -ie. they behave toward gear differentially
- -marked and unmarked animals suffer the same mortality
  - -tags often cause injury and infection
    - -may attract predators
  - -also violates the assumption if the marks render protection
- -marks are not lost or overlooked
  - -tags often fall off
  - -mutilation tags often grow back
  - -human error in examining animals for tags
- -under certain circumstances it is possible to test the randomness assumption
  - -eg. observations of behavior
- -reliability of propulation size estimates are determined with standard statistical methods
Measurements of relative density
- -these estimates represent some relatively constant, but unknown, relationship to total population size
- -note: all of the relative estimators should be viewed skeptically until the assumed relationship with density is studied
Life Cycles
- -we need to study life cycles in order to understand present population size and to make predictions about changes in population size
- -we need to quantify death and birth rates
- -in general, species are either
  - -semelparous: they have a single reproductive event in life and die eg. salmon
  - -iteroparous: they have multiple reproductive events in life
- -ecologist usually study life cycles by using a life table
  - -life tables allow the tabulation and examination of survivorship and mortality during the life history of the organism
  - -a life table is an age-specific summary of mortality rates operating on a population
  - -to set up a life table, we must decide on the age intervals to group data -species specific (eg. often for humans 5 year intervals are seen; mice 1mth)
  - - X=age interval
  - - Nx = number of survivors at the start of age interval X
    - -knowing these values, there is nothing "new" in a life table
      - -each of the other variables (lx, dx, qx, ex) are calculated
  - - lx = the proportion of organisms surviving to the start of age interval X, thus
    - lx = Nx / No (l2 = 34 / 142)
  - - dx = number dying during the age interval X to X+1, thus dx = Nx - Nx+1
    - (d2 = N2 - N3 = 34 - 20 = 14)
  - - qx = rate of mortality (proportion) during the age interval X to X+1, thus
    - qx = dx/Nx (q2 = d2/N2 = 14 / 34 = 0.412)
  - - ex = mean expectation of life for organisms alive at the start of age interval X, -first calculate the average number of individuals alive in each age interval
    - -called Lx
      - -Lx = number of individuals alive on average during the age interval X to X+1, thus Lx = (Nx + Nx+1) / 2
        (L2 = (N2 + N3)/2 = (34+20)/2 = 27
    - -Tx is a cumulative sum from the bottom of a life table in units of individuals multiplied by time Tx = Sum of Lx
      - (T2 = L2+L3+L4+...L8+L9 = 74)
    - - ex = Tx/Nx, thus e2 = T2/N2 = 74/34 = 2.18 age intervals
  - -lx (or Nx) is often plotted as a survivorship curve
    - -in general there are three types of survivorship curves
    - -Type 1: little losses at 1st but high losses in older organisms
      - -humans
    - -Type 2: contsant loss rate with age eg. many birds, buried seeds
    - -Type 3: high loss rates of young, little mortality of older individuals
      - -eg. many fishes, some invertabratesf
  - -How are life tables constructed?
    - -two general types:
      - -the static life table
        -its a cross section of the population at a specific time
      - -the cohort life table
        -where a cohort is a group of individuals all starting life during the same short time interval
        -cohort life tables are made by following the cohort throughout life
        -they tabulate the number of survivors at each age interval over the life span of all individuals
    advantages disadvantages
    
    static labor only reflects present conditions
    
    cohort reflect conditions over time labor
  - -life tables are made in ecology usually by
    - -directly observing survivorship (Nx)
    - -by observing age at death
      - -skeletal remains can be useful eg. African buffalo
  - -few generalizations can be made about life table data due to
    - -lack of information
    - -variation between species and even within species living in different ecological circumstances
Homework problem:
Determine the population size of a crayfish in a stream:
- -Capture and mark 277 individuals
- -Recapture 302, 112 of which are marked
- -Give the estimated population size, N^
- -Is the estimate biased by small sample size?
Data for hypothetical rats:

Age Group (months) (X) (Nx) lx dx qx Lx Tx ex

0-3 1 1249

4-7 2 820

8-11 3 730

12-15 4 505

16-19 5 405

20-23 6 225

24-27 7 75

28-31 8 35

32-35 9 0
Life tables summarize the mortality schedule of a population
- -in order to understand net population changes we need to consider reproductive rate
  - -more accurately, a combination of reproductive rate and mortality rate
- -One way to combine reproduction and mortality data is the use of demographic parameter "r"
  - -"r" is the innate capacity for increase in a population
  - -partially determined by the organism and partially by the environment
  - -environments vary continously
    - -thus "r" varies as well
      - -ranges from negative to positive values
  - -rm = maximal rate of increase
    - -usually set under lab conditions
      - -optimal food, optimal space, optimal physical parameters
      - -no predators or competitors
- -both birth and death rates vary with age
- -to eventually compute "r" we also need (in addition to the death rates in our life table) fertility table or bx function
  - -bx = number of female offspring produced per unit time per female aged x
Example:

Age Group (x) lx bx lx x bx = Vx lxbxX

0-14 0 0.9836 0.0030 0.0030 0.0

15-29 1 0.9751 0.6918 0.6746 0.6746

30-44 2 0.9583 0.2049 0.1964 0.3928

45+ 3 0.9453 0.0005 0.0005 0.0015= Sum 1.0689

Ro = sum of lxbx = 0.8745
Given lx and bx we can calculate a useful statistic
Ro = net reproductive rate per generation
- -Ro = Sum of lxbx = sum of Vx
- -Ro = 0.8745
If Ro = 1.0 the population is exactly replacing itself per generation
If Ro < 1.0 the population is decreasing per generation
If Ro > 1.0 the population is increasing per generation
In our example the population is decreasing at a rate of about 12% per generation (1-Vo)
"r" = ln(Ro) / G
- -where G is generation time
- -G can be approximated by the sum of lxbxX / Ro
G = 1.0689 / 0.8745 = 1.2223 time intervals (in years (1.2223)(15) = 18.3345 yrs)
"r" = ln(0.8745) / 18.3345 = -0.1097 per female per interval or /15 = 0.0073 years
Homework problem
Given for hypothetical rats:

Age Group (x) lx bx lxbx=Vx lxbxX

0-4 0 1.00 0.03 0.03 0.00

5-9 1 0.69 0.89 0.61 0.61

10-14 2 0.49 0.55 0.27 0.54

15-19 3 0.15 0.02 0.00 0.00

20-24 4 0.00 0.00 0.00 0.00
Calculate Ro the net reproductive rate/generation
Is the population increasing or decreasing?
Calculate "r"; the innate capacity for increase
- Ro = 0.91 9% negative population growth
- r = -0.07 female offspring per female per interval
Second Homework
N^= 747
S^2 = N^2 ((N^-M)(N^-C))/MC(N^-1)
- = 1870.1375
- s= �1870.1375
- = 43.2451 thus N^ = 747 +/- 43 Biased: (277)(302) > 4(747) = 83654 >> 2988 no bias
A population that is subject to a constant schedule of birth and death rates will gradually approach a stable age distribution
- -regardless of the initial distribution
When the population has reached the stable age distribution it will increase in numbers according to the differential equation: dNt/dt = rNo (Rate of change in numbers per unit time = innate capacity for increase times the population size)
Nt = Noe^rt where No = number of individuals at time 0 and Nt = number of individuals at time t e=2.7183(constant) and r= innate capacity for increase and t=time
logistic growth curves
The population grows until it reaches the carrying capacity (K) of the environment
- -eg. resources
  - -food, etc
- -competitors
- -predators
Homework: plot survivorship curve for first life table we calculated ***
-Many organisms fall nicely into one of two categories regarding the selection of life history traits
-There are so-called "r-selected" species
- -r is in reference to the geometric growth of a growth curve
-There are so-called "K-selected" species
- -K is in reference to the carrying capacity of the environment
-r-selected species have traits that promote the ability to multiply rapidly
- eg. (usually) small body size and short life span
  - -precocious reproduction (ie genetically closed program)
  - -large allocation to reproduction "walking or sitting gonad"
  - -man, but small offspring
    - -little investment in individual offspring
    - -semelparity
  - eg. annual plants and animals (fugitive species)
    - -weeds, many insects, other invertebrates, fish, etc
    - -often called opportunistic species
    - -usually first to colonize open habitat, distrubed area, etc.
-the second category is K-selected species
- -life-history traits that promote the ability to live in a community near carrying capacity are selected
- -traits include:
  - -relatively large body size
  - -long life
    - -delayed reproduction
    - -iteroparity
  - -smaller allocation to reproduction
    - -yet large investment per individual
    - -small number of individual offspring
  - -parental care
    - eg. many bird, mammals, redwood trees
Competitve interactions
-individuals of the same species require the same resources for survival, growth, and reproduction
-when immediate demand is greater than immediate supply we have the condition necessary for competition
- -within a species, competition is called intraspecific competition
- -whereas between speices, it is called interspecific competition
Definition: Competition is an interaction [between individuals] brought about by shared requirements for a resource in short supply, and leading to a reduction in the survivorship, growth, and/or reproduction of the competing individual.
Grasshopper Example
- -population of grasshoppers
- -eat grass - note they expand energy looking for grass and risk predation too
- -a grasshopper may find itself on a spot without grass because the grass was eaten by another hopper
- -this grasshopper must move: more energy for movement; less for growth or reproduction
  - -lower probability of survivorship due to greater exposure to predators
- -four above is due to competition
- -the more competitors our grasshopper has the greater their influence will be
Competition comes in two main forms:
- -exploitation competition
  - -little or no direct interaction between the competitors
  - -the intensity of the compitition is linked to the level of the resource
    - ie. it must be limiting
- -Interference competition
  - -individuals directly interact with each other
  - -they "interfere" with the use (or potential use) of a resource by others
    - ie. the defend, guard, or monopolize the resource even if it is not presently used
    - eg. territoriallity
      - -insects, fishes, birds, mammals, plants
  - -NOTE: competition often occurs for mates
    - -usually intraspecific interference competition
- -the effects of intraspecific competition are often density dependent
  - ie. little influence of competition with few competitors, but influence becomes greater with increases in number
  - eg. density-dependant mortality in Tribolium confusum(flour beetles)
mortality rate 0 >> 140 not increasing then linear increase
numbers dying 0 >> 140 expotential increase
numbers surviving 0 >> 140 negative parabola
Initial egg number (density)
1. density independent mortality
2. undercompensating density-dependent mortality (d.d.m.)
- -in under compensating ddm the increasing death rate is not enough to offset an increase in population size due to increasing density
3. over compensating ddm
- -in over compensating ddm death rate not only offsets potential population increase, but causes a decrease in population size
- -with initial increase in density, mortality is density dependent ie. we have a mortality rate due to things other than density
  - -this forms a base-line mortality rate
    - -density-dependant mortality must be shown above this rate
- -A less common phenomen is exactly-compensating ddm
  - -increases in density simply cause an equivalent increase in mortality
    - ie. above a certain density the number surviving remains the same regardless of density
- -fecundity is also often density dependent
  - -where fecunidty is generally defined as the number of eggs, or offspring, produced by an individual
- -example
  - -Melospiza melodia
    - -song sparrow on Mandarte Island, B.C. Canada
- -intraspecific competition may be capable of regulating population size
  - ie. because it keeps density within limits
- -even if either of the curves is density independent the curves cross and yield K
  - -where K represents a stable equilibrium
    - ie. populations below K grow and those above decline
- -population growth can be characterized by the net rate of recruitment
  - -the difference between the numbers being born and those dying results in net recruitment
  - -net recruitment has a typeical pattern;
    - -low: due to low density
    - -high: greatest differences between birth and death rates
    - -low: due to (eventually) over-compensating d.d.m.
  - -This results in an "n" shaped curve of net recruitment over density
    - eg. pheasant, flies, whales, plants
  - -given the typical "n" shaped net recruitment curve, population growth( numbers over time ) is typically S-shaped
LAB:Caption: number of branches as a function of nearest neighbor distince. There was a significant negative correlation (see text), n=35. for number of branches in relation to nearest neighbor distance, there was a significant negative correlation (Spearman Rank Correlation, n=35, rs = -0.671, P < 0.01).
- P/Q as a function of Veg. Cover(1-5)
- P/Q as a function of preserve, nonrange, range site
- pellet mass as a function of preserve, nonrange, range sites
- pellet mass as a function of P/Q
Interspecific Competition
- -Both casual and scientific observation have shown that populations of one species are often different (in terms of population growth) in the absense of a second species
- -relationships come in various forms
  - -Mutualism: both species benefit
    - eg. bacteria in a deer's stomach
  - -Commensalism: one species benefits and the other is unaffected
    - eg. algae on a turtle's back
  - -Parasitism: one is harmed and one benefited
    - -a form of predation
    - -a negative interaction
Logistic Growth Curve
dN1/Dt1 = rN1[(K1 -N1 )/K1 ]
N = population size
t = time
r = innate capacity for increase
K = carrying capacity
The basic rate of increase r1N1 is adjusted by how close N1 is to K1
- eg. if K1 = 100 and N1 is close to 0
  - -results in almost K1/K1 (approaches one)
Similarly, the rate of increase will slow as N1 approaches K1
- -results in growth rate approaching zero
In the case of interspecific competition, we have at least two species
- -thus, the growth of species 2 is dN2/dt2 = r2N2[(K2-N2)/K2]
The environment has a different carrying capacity for each species
- ie. the species are not equivalent
To look at the influence of competition, we need a conversion factor
- -coverts species 2 into the equivalent number of species 1 individuals
- eg. N1 = @N2, where @ is the conversion factor
Population growth of species 1 in competition
dN1/dt = r1N1[(K1 - N1 - @N2)/K1] or dN2/dt = r2N2[(K2-N2-@2N1)/K2]
- -this is simply the logistic growth equation where we have species 2 or 1 in equivalent terms to species 1 or 2
  - -AKA: Lotka-Volterra equations
the line represents dN1/dt =0 or no population growth
Populations of N1 in the hatched area will grow toward the line
- -those over the line will decline towards the line
Interspecific competition is understood through superimposing the graphs
- -this shows both lines ie. dN1/dt=0=dN2/dt
Four possible outcomes
- -N1 wins
  - -competitive exclusion
- -N2 wins
  - -competitive exclusion
- -Stable equilibrium
  - -co-exist
- -Unstable equilibrium(co exist)
Examples of Competition
- -yeast
- -competition between the floor beetle T. confusum and T. castaneum
  - -one species will drive the other to extinction in culture
    - -the result depends on the environment and starting conditions
      - -good example of unstable equilibrium
The competitive exclusion principle
- -"complete competitors cannot co-exist"
- -AKA: Gause's Hypothesis
- -How different do two species have to be in order to coexist in the same habitat
  - -we can adjust our expectations through the use of resource-utilization curves
Species try to minimize intraspecific and interspecific compeition through a change in the resource needs over time
Thus competition is thought to be a very important determinant of community structure
- ie. members of the community must not overlap much in their niches to coexist
Character Displacement
- -An evolutionary consequence of competition is the divergence of the species in sympatry
  - -the divergence is known as character displacement
- -character displacement is mostly inferred from observation
  - -four criteria are recommended (Arthur 1982) before a conclusion regarding character displacement can be made
    - -1. The change in mean value of the character in areas of overlap should not be predictable from variation within areas of overlap or areas of isolation
    - -2. Sampling should be done at more than on set of locations so that local effects can be eliminated
    - -3. Heritability of the character must be estimated to be high so that genetic variation may be assumed to underlie the idfference observed
    - -4. Evidence must be presented to show that the species are indeed competing and that the character measured has some relevance to the competitive process
- -even the Galapagos finch example only meets conditions 1 & 3
  - -1: change in beak size is greater than expected due to chance
  - -3: beak characters have been shown to be heritable
  - -2: only seen in one place
  - -4: no definitive evidence of competition
- -Thus the phenomenon of character displacement may be common, but very difficult to demonstrate

Predation

-"Consumption of one organism by another organism in which the prey is alive when the predator attacks it"
-Two main forms of classification:
- -By taxonomy of what they eat:
  - -Carnivors: eat animals
  - -Herbivors: eat plants
  - -Omnivores: eat both animal and plant
- -By function - how they eat
  - ie. their relationship with prey
  - -true predators: prey die immediately after attack
    - -use of several or many prey individuals over the life of the predator
    - eg. lions, tigers, snakes, eagles, etc
  - -grazers
    - -attacks rarely lethal in the short term
    - -remove only parts of prey
    - -attack large numbers of prey over the life time of the predator
    - -eg. sheep, cattle, etc.
  - -parasites
    - -attacks rarely lethal over the short term
    - -remove only parts of prey
    - -unlike grazers utilize only one to few prey over the life of the predator
    - eg. tapeworm, measles virus, lice, mosquitos
  - -parasitoids
    - -attacks not immediately lethal, but eventually are
    - -remove parts, eventually the whole prey
    - -one to few prey in the lifetime of the predator
    - eg. some wasps (order Hymenoptena), true flies (order Diptera)
    - -parasitoids are important - they represent about 25% of known species

	# of prey	immediately lethal	eventually lethal	% consumed
True Predators	Many	YES	-	large
Grazers	Many	NO	small removal-No	small-large
			large removel-Yes
Parasites	One to few	NO	small load - No	small
			large load - Yes
Parasitoids	One to few	NO	YES	eventually large

Lecture Three

Herbivory is a good model to discuss predation because herbivores can act as 3 of the four types of functional predators
- -true predators, grazers, and prasitic consumers
How do plants respond to predation?
- -effects on the population of the consumed are not necessarily simple harmful
  - -some benefits may accrue
Plants compensate when eaten
- -results depend on where on the plant herbivory occurs
  - -net increase of photosynthesis may increase if self-shading is reduced
    - eg. removal of upper canopy
  - -balance between photosynthesis and respiration may improve if the lower canopy is attacked
    - -low(shaded) leaves respire, but have low rates of photosynthesis
  - -mobilization of stored carbohydrates
    - -including a change in their distribution
      - eg. defoliation of grasses often stops root growth
        -energy is now shunted to new shoots
    - -redistribution may also compensate for loss of reproductive potential
      - eg. in soybeans, Glycine max
        -remaining pods receive more photosynthate and the weight of seeds is increased
        -results in an increase in the probability of survival
  - -increase in the rate of photosynthesis of remaining leaves
    - -unit leaf rate
      - ie. plants become mroe efficient
  - -Energy Flow
    - -Sources: leaves
    - -Sinks: buds, roots, tubers, sucking herbivores
    - -Decrease source >>>> increase Unit Leaf Rate
    - -Increase Sink >>>>>>increase Unit Leaf Rate
  - -many plants have naturally high rates of flower death before producing fruit or seed
    - eg. wild parsnip (Pastinaca satira)
      - -herbivory reduces the death rate of flowers usually not utilized
  - -Entire compensation is rare
    - -plants are usually harmed by herbivory
      - - sometimes disproportionately so
        eg. ring-barking
    - -slugs eating the meristem of grasses at the base of their shoots
  - -Sometimes, instead of compensating plants produce defensive structures or compounds
    - -thorns or prickles that may become longer or sharper on secondary growth
      - eg. dew berries
    - -"rapidly inducible" defences
      - -usually chemical: example- protease inhibitors
West 1985
- -used oak tree Quercus robur (pedunculate oak) and a leaf miner phyllonorycter species
  - -leaf miners are moths
  - -about 25% of leaves were removed by experiment
    - -also natural leaf damage was examined
  - -found a negative correlation between damage to the leaves and percent survival to adulthood in the leaf miner
Herbivory is often a mutualism!
- -herbivores are often pollinators or vectors of dispersal
General Effects of (Herbivory) Predation
- -usually harmful to the individual prey
- -does not follow that predation is generally harmful to a population
  - -killed are usually not taken randomly
    - -injured, sick, young, least competitive (those without shelter or territory)
    - -usually have low reproductive potential
- -individuals that escape predation often compensate for those taken
  - -the population may compensate for predation in high-density populations by an increase in net recruitment rate
Influences of Prey on Predators
- -successful predation often occurs as threshold events
  - -survival
  - -growth
  - -reproduction
- -prey often respond to predators through synchronous reproduction
  - -"predator swamping"
  - eg. coral-reef fishes
    - -daily or lunar spawning events that are highly synchronous
  - eg. "masting" in trees
  - -ensures some years have good recruitment due to predator swamping and that swamping is usually a successful tactic due to the time lag in the response of the predator population
- -finally, food quality can be as influential as food quantity
Aposatic selection
- -virtually all predators eat more than one type of prey
  - -different species
  - -different morphs from polymorphism
  - -different phenotypes
- -Random selection of prey would require that they are taken according to their availability
  - -instead prey are usually taken differentially
    - -more common forms, or species, are usually preferred
      - -this selection is called apostatic selection
  - -"Search Images" have been thought to be causative in apostatic selection
    - ie. an "image" of the prey in the predators brain
    - -reference is often made to interference between search images, but there is little direct evidence
    - -Alternatively the "optimal search rate hypothesis" asserts that aposatic selection occurs due to local prey density
      - -views the world as patches
      - -predators move between patches in search of prey
      - -Example of "decision rules" for when to leave a patch
        - "Marginal Value Theorem"
        -world exists as patches
        
        -predator spends Tt travel seconds traveling to a patch and consumes food according to a gain curve
  - -note resource depression
    - -gain curve falls off if the predation stays in the patch a long time
- -When should the predator leave the patch?
  - -optimal foraging theory predicts that the animals that maximize the energy gain per unit time will be the most successful
Tangent method of finding the optimal time to leave the patch, T sub opt
- ie. maximization of the Engery (E) / time (T) ratio
- -line AB has a slope of E/T
  - -it must touch the gain curve, and the steepest slope yields the best E/T ratio
- -the predator should leave the patch at T sub opt
  - -gains diminishing returns after this point
    - ie. their value becomes more and more marginal
- -Note that longer times in travel result in a greater time in the patch
  - -(Note: even without any changes in the gain curve)
- -it becomes more worth while for the predator to explore the diminishing returns portion of the curve
Anti-predator behavior:
- -first understand the effects of predation:
  - Direct: Death
  - Indirect: complex and variable
    - -morphology
    - -physiology
    - -behavior
Anit-predator behavior: actions preformed by potential prey to reduce the probability of predation

Examples:

Defense:	morphology	Examples: porcupines, blowfish, and frilled lizard
	biochemical	Examples: plant toxins, frog, toad toxins, skunks, poisonous
Avoidence:	temporal	Examples: Deer
	spatial	Examples: amphibians
Escape:	Confusion	Examples: lizard tail
	Speed	Examples: Gazelles

Predator-Specific Anti-predator behavior:
- -actions preformed by potential prey to reduce the probability of predation by specific predators
- -allows increased efficiency of anti-predator behaviors
- -Two-Step Process:
  - -Identification of predator
  - -Response to predator
Costs of Anti-predator behavior:
- -expenditure of energy
- -increased visibilty to other predators
- -reduction of mating opportunities
- -reduction of foraging/maintenance
Costs and Benefits of Anti-predator behavior
- Benefits: increased survival which yeilds increased opportunities for reproduction
  - -proper identification and response is necessary to yeild benefits
- -Costs: decreased survival which yeilds decreased opportunities for reproduction
  - -improper identification or response
Selection should favor proper identification and response
Predator Specific Anti-predator behavior examples
- -Rattlesnakes
  - -Rattling: common response to large mammal
  - -Ophiophagus Ophidian Defensive Behavior
    - -(Snake-eating snake): NM Kingsnakes
      - -body bridging and head hiding
How might patch variation influence optimal time in a patch?
- -the model predicts that each patch should be used until the gain rate drops to the average for the environment
  - -translates into shorter times in < average patches, and longer times in > average patches
Assumptions of the model
- -Each patch type is recgnized instantaneously
  - -slop in the predictions results if this assumption is not met, otherwise an assessment time would be needed before decisions are made
- -Travel time is known
- -Gain curve is smooth and continuous and decelerating
  - e.g. variability in the curve would make predictions less straight forward
- -Travel time and searching in a patch have equal costs (otherwise corrections are necessary)
Predictions
- -If travel time and gain curves are known, Topt can be predicted
- -Greater the one patch type should result in the types being used to the same marginal gain rate
There are few test of the model, but they are generally good
- -best example uses great tits, Parus major,
  - -Time in a patch increases as predicted with travel(handling time)
  - -observed times in patches (dots) are not significantly different from the line predicted by the marginal value theorm
    - -Birds were given pots of meal worms
      - -each pot had the same number of worms (gain curve is the same)
      - -lids differed in difficulty of removal
        -varied handling time
        -handling time was substituted for travel
Responses of Prey
- -Polymorphism can be advantageous
  - -with two or more forms, predators may switch(aposatic selection) to a different species when the preferred form becomes rare
    - -reduces the overall risk per individual (Note: at the level of the individual, thus not a group-selectionist argument)
Cryptic coloration(or other sensory modality) - resembles a random sample of a background
- -advantageous to prey
- -not necessarily dull
- -cryptic coloration depends on both the background colors(patterns) and the preception of the predator
  - eg. insects can often see into the ultraviolet range
Some poecilid (live bearing) fishes have conspicuous red spots
- -used in intraspecific communication
  - eg. sexual selection
    - -females prefer to mate with males with more and larger spots (at least these males have greater mating success)
- -Endler and others have shown in the 1980's that there is a tradeoff between crypsis and and the intraspecific communication
  - -work with guppies, poecilia reticulata from Trinidad shows a tradeoff between # of spots and predation
    - -guppies with larger and more spots have a greater risk of predation but also have an advantage in mating
  - -the opposite of cryptic coloration is aposematic coloration
    - Aposematic coloration - stands out against the background
    - -"warning colors"
    - -these animals stand out against a background
    - -eg. bees, scorpion fish, coral snake
    - -often combines conspicous coloration with noxiousness
      - -includes being toxic, unpalatable , or even dangerous to the potential predator
    - -protection should increase with the density of the signal
      - ie. predator may learn through encounter
Point-to-Plant Distance Ratio and a t-test for comparison of a mean with a standard
Hypothetical Data Set - Dandelion distances from random points in space

Sample P1(mm) P1^2 P2(mm) P2^2 P1^2 / P2^2 = Xi Xi^2

1 3 9 10 100 0.0900 0.0081

2 5 25 8 64 0.3906 0.1526

3 10 100 12 144 0.6944 0.4822

4 9 81 10 100 0.8100 0.6561

5 18 324 25 625 0.5184 0.2687

6 4 16 6 36 0.4444 0.1975
"A" is the coefficient of aggregation
A= Sum Xi / n = 2.9478 / 6 = 0.4913
Note that the coefficient of aggregation, "A" equals 0.5 for a random distribution
Uniform distributions result in values of "A" significantly less than 0.5
Aggregated distributions have "A" significantly greater than 0.5
To test for significant differences, we will use a t-test for comparison of a mean with a standard
Ho: The mean (A) is not significantly different from the standard (0.5)
HA: The mean (A) is signficantly different from the standard (0.5)
- -if the |t| greater than or equal to t-critical, reject Ho
where t = mean - standard / standard error
and mean = "A"
t = (.4913 - .5000) / (s / square root of n)
s = square root of s^2
s^2 = sum of Xi^2 - ...
S^2 = 0.0634
s = 0.2518
standard error = s / square root of n = 0.2518/ square root of 6 = 0.1028
t = (-0.0087)/ 0.1028 = -0.0846
Evolution of unpalatability
- -unpalatability is rare, ie it is a derived condition
- -unpalatability (or noxiousness) often operates after tissues are severly damaged or after ingestion
- -how does unpalatability evolve?
- -if prey escape to reproduce it follows that natural selection favors the evolution of the character
  - -yet if they do not survive
    - -kin selection is a possible solution
      - -many distasteful species aggregate
        eg. butterflies, especially when catapillers
  - -eventhough an individuals direct fitness is lowered its inclusive fitness may increase if it increases the survivorship of kin
    - ie. the individuals gene frequencies increase in the next generation because it shares many genes with kin
- -Inclusive fitness: a measure of fitness due to the reproductive success of an individual plus the reproductive success of relatives which share genes
Alternatively, even without kin selection, aggregation may be advantagous due to faster learning by predators
- -What about the brightness of aposematic colors?
  - -why use conspicupusness as a warning?
    - -rapid learning: learning is faster when unpalatability is paired with conspicousness
    - -conspicousness is easier to associate with unpalatability due to lack of complexity
    - -new(novel) patterns are easier to learn
      - -may lead to faster learning
    - -detection: distance model
      - -asserts that fewer recognition errors over crypsis may make conspicousness advantagous
        ie dectection is from further out
      - -more time for predator decision; may result in fewer errors
- mimicry: advantages due to conspicousness may lead to mimicry
  - -batesian mimicry
    - -a patatable species resembles an unpalatable spieces
      - eg. Viceroy butterfly mimicing monarch butterfly
  - -Mullerian Mimicry
    - -a less palatable species mimics a more unpalatable species
      - eg. Papilio butterflies
Community Ecology
- -a community is an assemblage of species populations which occur together in space and time
  - -a community has collective properties
    - -species diversity (numbers and abundance of species)
    - -community biomass
    - -productivity: productioon of new biomass per unit time
  - -communities also have emergent properties
    - -a community is more than the sum of its parts
    - eg. the interactions between community members give added dynamics to community structure
  - -a primary aim of community ecology is the determination of repeating (and predictable) patterns of community structure
Description of community structure is difficult
- -a need exists to describe complex phenomena in simple ways
- -recognition of patterns leads to higher levels of study
- -community structure is studied at various scales
  - -appropriate scale depends on the questions asked
Species richness is the number of species present in a community
- -take samples until the number of species reaches an asymptote
- -instead, people often compare communities that have equivalent samples (or effort) -a
- primary aim of community ecology is the determination of repeating (and predictable) patterns of community structure
- -species richness does not account for species abundance
  - eg. community A 10 species 91% of one and 1% of each of the others
  - community B 10 species 10% of each
Such questions lead to the development of diversity indices
- -account for both number and abundance of species
  - -one of the most common indices is Simpson's index D where
    - -D = 1 / sum of Pi^2; s=number of species and Pi=proportion of the species in the community: Dmax = s
Patterns in Space
- -community boundaries usually do not exist
  - -we should think of communities based on the probability distribution for each community member
  - -there is a problem in defining the community due to the subjectivity in the characteristic of the environment examined
- -Ordination is a technique employed to reduce the subjectivity
  - -we examine whether communities "cluster" when analyzed for common traits
    - eg. relative abundance of species
  - -ordination is a mathematical treatment that results in communities with both similar species composition and relative abundance
- -After ordination, interpretation takes place by examination of the environment variables
  - -classification assumes that communities are discrete and deterministic
    - ie. a given environment will most likely lead to a specific type of community
- -A problem exists with this interpretattion in that it does not account for random processes in the determination of community structure
  - -community structure is no longer viewed as a "superorganism"
    - -most recently "lottery hypothesis" of Sale (1980's) in community structure
    - -this idea asserts that communities in particular environments are similar due to having species with similar requirements
    - -work of Doherty (80's and 90's) has shown that the long term community structure on coral reefs is more supportative of a random model than one that is deterministic
    - -Truth is likely a continuum
    - -Stochastic processes (random)<---------------->deterministic processess
  - -The benefit of classification is environmental monitoring
    - -some communities are more tolerant of pollution (or other change)
- Indicator species - species used to monitor complex community structure
  - -usually the first species lost after disturbance
  - -"early warning"
  - e.g. marine butterfly fishes
Patterns in Time
- -Succession
  - -defined as "the non-seasonal and continous pattern of colonization and extinction on a site by species populations"
- -Degradative Succession
  - -involves the changes in community structure as a resource is degraded
  - eg. fungal populations on pine needle litter on a forest floor
- -Autogenic Succession (self made succession)
  - -results from biological processes that modify an environment
  - eg. early plant communities modify soil such that different species are then, more successful
- -Allogenic Succession
  - -succession is largely due to physical changes in the environment not due to biological factors
- -Successions are also classified as primary or secondary
  - -Primary
    - -virgin area
  - -Secondary
    - -disturbed area
- -Interactions
  - -species can facilitate succession
    - ie. they make the environment suitable for the next species or community
  - -species can inhibit succession
    - eg. Ulva v. Gigartina
Mechanisms
- -Probabilistic Transistion
  - eg. trees
  - -probability determined empirically by percentage of saplings under adult trees
  - -gives the replacement probability over time
    - -allows a simulation of succession
- -Tilman's Resource Ratio
  - -different species of plants require different optimal ratio's of light and nutrients
  - -ecosystem pattern is generally toward less light and greater nutrients
    - -results in succession
  - -r and K species mechanism; r species early; K species later
Climax Communities
- -do they exist?
- ie. a pinnacle of community structure
- -great concept, but communities are always changing
- -matter of scale
  - -large scale - climax community can be a useful concept
    - eg. stable tree distribution
  - -small scale - not very useful; succession starts over with every disturbance
Species - Area Relationships
- -long known that islands have fewer species than the same size areas of mainland
- -species richness declines with the size of an island
- -such species-area relationships can be observed on many "types" of islands
  - -kipukas
  - -lakes
  - -mountain tops
  - -types of soil
  - -etc
How does isolation influence community structure?
- -to have a better understanding of community structure biologists need to know something about island biogeography
  - -Three main approaches:
    - -Habitat diversity: concentrates on how suitable islands are for immigration
    - -Equilibrium Theory: looks at the potential balance between colonization and extinction on an island
    - -Evolutionary Approach: focuses on the balance between colonization and the evolution of new species
Habitat Diversity
- -larger areas contain more species simply because they have more types of habitat
- -largely from the work of Lack (60's and 70's) on birds
- -idea was that dispersal was not a limiting factor
  - ie. getting to an island but finding the right habitat
- -major weakness is that it fails to recognize that dispersal ability is a major barrier to most species
- -it also fails to recognize that a present community may also reflect evolutionary processes on the island
Equilibrium Theory
- -MacArthur and Wilson (76)
- -the number of species is a reflection of the relationship between immigration and extinction
- -dynamic equilibrium
  - ie. the process is continuous
  - -immigration and extinction are ongoing
  - -immigration rate will be high at first, slow as an island approaches the # of species from the source
- -extinction rate rises the # of species present
  - -smaller population sizes have a higher probability of extinction
    - -thus, smaller islands have a higher probability of extinction
  - -S* represents a dynamic equilibrium where the immigration and extinction curves cross
  - -Predictions
    - -species richness should become roughly constant at S*
    - -the constant number is from turnover
    - -larger islands should have more species
    - -remote islands should have fewer species
  - -Evidence
    - -influence of habitat
      - eg. communities of fishes in Australian Springs
      - -relationship between species richness and area was caused by a strong correlation between spring size and # of habitats
      - -as pools get bigger they have more habitats
    - -Alternatively, birds show a strong relationship with area, but not habitat diversity
    - -Simberloff reduced island size of mangrove islands off Florida
      - -despite small smaple sizes, Simberloff showed a direct relationship between island size and species richness
    - -remoteness may also affect # of species
      - eg. birds
    - -the remnant of Krakatau island, Rakata island, makes a good example of following community structure from primary succession
      - -numerous surveys of the accumulative of new species and extinction
    - -Disharmony
      - -disproportional representation between a mainland and island
      - -another general point is that generalists are less likely to go extinct
  - -Evolution and Island Biogeography
Conservation and Biodiversity
- -more than 99% of species that ever existed are now extinct
  - -most species last, on average, about one to ten million years
    - -given about 10 million species on earth
    - -results in a prediction of 0.001 - 0.01% of species lost each century
  - -current extinction rate of birds and mammals is about 1% per century 100 - 1000x the 'natural' rate of extinction!
- Why Conserve?
  - -Our own preservation
  - -The value of biodiversity "ecological economics"
    - -Direct Economic Value
      - -food
      - -about 40% of drugs are being derived from organisms
      - -control agents
    - -Indirect Economic Value
      - -about 200 million ppl enjoy nature recreation
      - -$4 billion industry in the US
      - -$12 billion worldwide
    - -ethical value
      - -animal or organism rights
  - -Conservation of Biodiveristy
    - -species richness
      - -smaller scale
        -conservation of populations to preserve genetic diversity
      - -larger scale
        -whole communities
    - -Thus far conservation has focused on the species level
      - eg. vulnerable species
        -10% prob. of extinct in 100yrs
      - endangered species
        -20% prob. of extinction in 20yrs or ten generations
      - critical species
        -50% prob. of extinction in 5 yrs or 2 generations
    - -Based on these criteria 43% of all vertebrates are threatened
    - -species at high risk of extinction are usually rare
      - -what is rare?
    - -Rarity can be natural or due to interactions with humans
      - -over-exploitation
      - -Habitat disruption
        -habitat destruction
        -habitat degradation
        -habitat disturbance
        -introduced species

Ecology Paper:

A Comparison of Two Different Approaches to the Determination of the Distribution Pattern of Taraxacum officinale on the Campus of Eastern New Mexico University

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	advantages	disadvantages
static	labor	only reflects present conditions
cohort	reflect conditions over time	labor

Data for hypothetical rats:
Age Group (months)	(X)	(Nx)	lx	dx	qx	Lx	Tx	ex
0-3	1	1249
4-7	2	820
8-11	3	730
12-15	4	505
16-19	5	405
20-23	6	225
24-27	7	75
28-31	8	35
32-35	9	0

Age Group	(x)	lx	bx	lx x bx = Vx	lxbxX
0-14	0	0.9836	0.0030	0.0030	0.0
15-29	1	0.9751	0.6918	0.6746	0.6746
30-44	2	0.9583	0.2049	0.1964	0.3928
45+	3	0.9453	0.0005	0.0005	0.0015=	Sum 1.0689
				Ro = sum of lxbx = 0.8745

Age Group	(x)	lx	bx	lxbx=Vx	lxbxX
0-4	0	1.00	0.03	0.03	0.00
5-9	1	0.69	0.89	0.61	0.61
10-14	2	0.49	0.55	0.27	0.54
15-19	3	0.15	0.02	0.00	0.00
20-24	4	0.00	0.00	0.00	0.00

Sample	P1(mm)	P1^2	P2(mm)	P2^2	P1^2 / P2^2 = Xi	Xi^2
1	3	9	10	100	0.0900	0.0081
2	5	25	8	64	0.3906	0.1526
3	10	100	12	144	0.6944	0.4822
4	9	81	10	100	0.8100	0.6561
5	18	324	25	625	0.5184	0.2687
6	4	16	6	36	0.4444	0.1975