Ec271 2Nd Exam

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community

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-all species found in a specified area
-influenced by biotic and abiotic factors

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closed community

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-CLEMENTS
-holistic organization
-abrupt border between communities
-coincident species range
-extensive coevolution
-interrelationships within communities

-a community functions like a superorganism
-Closed, meaning a group of species would appear or disappear from a community as one moved along some environmental gradient.
-Clements' idea of succession is that a group of species should arrive early in sucession, alter the habitat in some way (preparing the way for the arrival of later arriving species) and that those earlier successional species should disappear from the community at once.

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open community

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-GLEASON
-popular theory
-individual organization
-diffuse border between community
-independent species range
-coevolution uncommon

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ecotones

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abrupt boundaries between communities (Clements)

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gradient analysis

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-used in plant community ecology to relate the abundances of various species in a plant community to various environmental gradients by ordination or by weighted averaging
-ex: moisture and altitudinal

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when do we expect closed communities?

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1) abrupt physical boundaries
2) at geographic limit of a dominant species

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community structure

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quantitative description of the species in a community

includes:
-# of species
-density of species
-relative density

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relative density

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-relative abundance

-proportion of individuals of a particular species / total # of individuals of all species in the community

-tells us what's common
-also displays logarithms

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Preston's lognormal distribution

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-shows quantitative abundance
-x axis doubles (logarithmic scale)
-you get bell curve (mostly normal species)

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Witiker diagram

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supports Gleason

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relative importance

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= relative density + relative dominance

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different ways to determine dominance in a community

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-relative density, dominance, or importance

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how do we determine "size"?

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biomass

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components of diversity

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1) species richness
2) species evenness

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species richness

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-# of species you have

-bigger islands have more richness

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species evenness

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-the relative abundance of species in a community

-how evenly individuals are distributed among species; higher evenness yields higher diversity

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rank abundance curves

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-rarer the further you go down
-y=relative abundance
-steep slope = less evenness
-shallow slope = high evenness
-shows evenness and richness

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what does impact of canopy size on bird diversity tell us?

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-there's a strong relationship between habitat complexity and diversity

-x: warblers partition themselves according to height
-least complex on ground

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definition of ecology

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"the study of the interactions (the why) that determine the DISTRIBUTION and ABUNDANCE of organisms"

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community organization?

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-descriptive (who and how many)
-tells little about interactions in community; we can infer however
-tells us WHO and HOW MANY

-add or remove species in experiments

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community organization

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-study of interactions that shape community structure
-why are they different? community structure says they are!

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what organizing interactions determine distribution and abundance?

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1) predation - predator in/exclusion experiments

2) competition - intra/interspecific; when resources are limited

3) disturbance - episodic event; unpredictable; most important
a) physical - x: boulder destroying intertidal zone
b) biological - x: moose walks thru garden

4) physical factors - chronic or predictable

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foodwebs

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-demonstrates community organization
-shows interactions
-which arrows are most important?

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intermediate distribution hypothesis

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-max species richness occurs at intermediate predation level
-equilibrium between herbivory and predation

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keystone species

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-influence community disproportionately to their biomass
-exerts large impact of community organization even though its not common
-drives the system
-determines species richness

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succession

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-"community development"
-predictable and orderly changes in the composition or structure of an ecological community
-primary and secondary
-how it gets started and changes over time
-way of looking at community ecology

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primary succession

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-species replacement that occurs in a new habitat area
-habitat created from nothing

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secondary succession

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-established community is DISTURBED by event, therefore community structure changes

-already established ecosystem reduced to a smaller population of species

-common

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pioneer species

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-good dispersal abilities
-x Mt St Helens spiders

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climax species

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-community that essentially maintains itself
-x understory same as canopy (hemlocks in arboretum)

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why are there so few plants early in succession?

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-different dispersal abilities
-soil is lousy
-cause low initial diversity
-species come in and "prepare the way"
-x alder's N-fixing abilities
-not constant with evolution though because they are seemingly happy dying

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what are the 3 ways earlier arriving species interact with new species

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1) facilitation
-positive attribute
-orderly
-facilitated

2) tolerance
-"take it or leave it"
-expect climax to dominate but to get there slowly because of bad dispersal

3) inhibition
-negative attribute
-species hold on to keep out other species
-not "orderly replacement" but a war!

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facilitation

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(least popular)
-positive attribute
-orderly
-facilitated
-mostly in primary succession

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inhibition

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(most popular)
-negative attribute
-species hold on to beat out other species
-not "orderly replacement" but a war!

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tolerance

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(moderately popular)
-"take it or leave it"
-expect climax to dominate but to get there slowly because of bad dispersal

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population biology

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ecological attributes of a single species

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3 basic patterns of population distribution

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1) random
*most common
-neutral interaction
-interactions aren't important
-population is small
-x predators

2) regular
*least common
-antagonistic
-strong interactions
-competition within species
-antagonistic (negative, negative)
-x honeycomb

3) clumped
-attraction between individuals or to a common resource
-usually related to clumped resources

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survivorship curves

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-follows cohort through time
-we want to efficiently look at how species dies over time
-semi-log plot gives you straight line
-slope gives survivorship at t

# of x / t

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constant survivorship

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50% die, 50% live

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stable population

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λ = 1

r = 0

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ℓx

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-proportion of original cohort that is alive over t
-can only decrease

Sx

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age specific fecundity

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how many offspring are produced at given t

mx

Fx

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λ

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-finite rate of increase

∑ lxmx

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Leslie matrix

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-better technique
-used by conservation biologists to help manage population by increasing survivorship
-can't change fecundity though

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sensitivity analysis

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improve various paremeters to see effects (hopefully positive) on population growth rates

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instantaneous growth rate

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r

instant. birth rate - instant. death rate

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carry capacity

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k

-"attractor"
-everything gravitates towards it

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r-selective species

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-"fugitive species"
-high dispersal
-high reproductive rate (r value)
-poor competitor
-inefficient use of resources
-short life span
-ex: dandelion

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k-selective species

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-low dispersal
-low reproductive rate (r value)
-excellent competitors
-efficient use of resources
-long life span (no hurry to reproduce)
-near k on curve
-ex American beech

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2 ways of looking at predation

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1) strict sense
-1 animal eating another

2) broader sense
-scientific
-one organism feeding on another

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types of predatory relationships

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-non-lethal predation
-predator-prey
-herbivore-carnivore
-host-parasite
-victim-exploiter

-winners and losers

-always energetic costs

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functional response Type I

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-x-axis = prey density
-y-axis = #prey/pred/unit t
-linear
-food requires no handling time
-if you double prey, you'll see doubling in predation rate

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functional response Type II

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-x-axis = prey density
-y-axis = #prey/pred/unit t
-significant search and handling time
-increase prey density and curve goes up quickly but becomes asymptotic because of handling time
-search time negligible and handling costs fixed at K

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functional response Type III

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-x-axis = prey density
-y-axis = #prey/pred/unit t

-S-curve
-handling time
-search image formed at higher densities
-increased familiarity has affect on efficiency of search
-causes switching behavior

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switching behavior

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-predators concentrate on a particularly common species of prey when it becomes energetically efficient to do so

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masting

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-huge production of seeds by plants presumably to overwhelm seed predator

-form of predator satiation

ex: eucalyptus trees in Ausi release tons of seeds following fire to overwhelm ants

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predation satiation

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-antipredator adaptation in which prey occur at high population densities, reducing the probability of an individual organism being eaten

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competition

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interactions between 2 organisms for a limiting resource

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limiting resource

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-short enough supply that there are negative effects

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what does competition manifest as and result in?

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-decreased survivorship (increased mortality)
-decreased growth (delayed reproduction)
-decreased reproductive effort (don't produce enough seeds, flowers, babies)

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mechanisms of competition

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1) indirect, exploitative competition

-ice cream example
-2 girls eating with 2 different sized spoons

2) direct, interference competition

-ice cream example
-hitting the other with spoon

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zonation patterns are determined by:

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-physiological stresses
-competition

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self thinning

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-reduction in population density as a stand of plants increase in biomass, due to intraspecific competition

-largely occurs with plants
-start with different number individuals (A,B,C,D)
-converge at state of low density and high total biomass
-large plants with low density
-survivorship down
-development time up
-body size down
-too many plants so they compete

-example of intraspecific competition

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competition coefficient

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-translator

-summarizes the effect of one species on another

α

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niche

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-place and function of organism in its environment

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fundamental niche

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-an n-dimensional hypervolume
-the full range of environmental conditions (biological and physical) under which an organism can exist

-established by Hutchinson

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realized niche

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-smaller niche an organism is restricted to due to competition

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competitive exclusion principle

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-no 2 species with similar physiological constraints can occupy the same niche
-they would become out-competed

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what is relative density?

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-relative abundance
-the proportion of individuals of a particular species divided by total number of individuals of all species in the community

-species evenness too

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relative dominance

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-proportion of the total basal area of a species / the total basal area of all species in the community

-used with trees

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refuge

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-secure place where exploiter has limited access to prey

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Shannon-Wiener Index

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H'

-diversity index used to measure diversity in categorical data

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systems where exclusion of predator results in decreased species diversity only works when predator favors competitive dominant

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presence of predator maintains species diversity only when it preys on competitive dominant

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asymmetric interspecific competition

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-where one species has a strong competitive effect on a second species but the reverse does not occur

-occurs when one of the two competing species is much larger or stronger than the other species.

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dominant species

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-have significant influence on community structure by virtue of high biomass

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slopes of semi-log plots for age specific survivorship

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flat slope = low mortality

steep slop = high mortality