COMMUNITY ECOLOGY EXAM 3

What are ecological networks

attempt to summarize the multitude of potential interactions between species within a community by representing those species as nodes in the network and using links between nodes to represent interactions between species. Ex. food webs, parasite-host nets, plant pollinator nets, seed disperser nets

Why do we care about the structure of ecological networks

help us to predict how an ecosystem functions, stability, complexity, interactions, conservation

how do we quantify the structure of networks

complexity, stability, networks quantify interactions ie. how strong or weak they are, body size, indirect and direct effects, nestedness, modularity, connectance

How do we determine the bounds of a network

physical properties of the habitat/ecosystem they reside in, the type of interactions that occur as well as how many there are, movement of organisms

what components comprise networks and what do they represent

community, sink web, source web, green web, brown web, trophic levels and positions, links, nodes, complexity, stability,

What are some emergent patterns in networks

FEW STRONG MANY WEAK

How does network complexity affect ecological stability

more complexity means higher stability, however theoretical systems show more complexity means less stability

What are some remaining challenges in our understanding of ecological networks

• objective quantification of food webs that allow comparability across and within ecosystem types

• determining node and link resolution

• integration of spceis traits

• inclusion of paratism

What are trophic cascades

non-adj. trophic level affects the abund./biomass of a lower trophic level (indirect effect)

How does food-chain length affect rel. importance of factors structuring communities

top-down affects (predator driven), and bottom-up affects(resource driven)

How does energy availability and FCL affect equilbrium biomass

equilibrium biomass is high when there is no predation, on the organism, only comp determines their pop size. When predation is high on an organisms then their equilibrium biomass is lower. equilibrium biomass increases with increase in FCL

Distinguish between consumptive and non-consumptive effects

consumptive - density-mediated

non-consumptive - trait mediated

Distinguish between bottom-up and top-down effects in food chains

bottom-up: resource driven; producers drive the food chain (odd FCL’s)

top-down: predator driven; highest predator(s) has great affect on whole food chain/network (even FCL’s)

Distinguish potential determinants of food-chain length

competition/predation on either the producer or the highest predator

What is community assembly

process that shapes identities and rel. abund. of sp. within ecological sommunitites (what species, where, and why)

Understand the habitat template, ideal free distribution and assembly rules concepts

habitat temp: species distributed across landscape in relation to env. gradients, as habitat stability increases and habitat stress decreases the biotic effects on community increase

IFD - species occur in relative abundance to maximize growth; integrated trade-offs in optimal physical env. and comp/predation

Assembly rules - species can be added to assemblage if certain rules or traits of local assemblage are met

what are life history strategies

equilibrium: high juvenile survival, low fecundity, late maturity/long life/long generation time

periodic: low survivorship, high fecundity, long generation time

opportunistic: low survivorship, low fecundity, short generation time

Understand trade-offs in demographic traits in the EPO life-histroy model

Equilibrium: trade fecundity for high survivorship and generation time

Periodic: trade survivorship for high fecundity and generation time

Opportunistic: trade everything for ability to survive in harsh environments

How do multi-scale env factors and biotic interactions contribute to community assembly

env factors and biotic interactions filter out the organisms in the same regional pool, and local pools into the specific community. The organisms filtered out don’t fit the niches needed for that community.

What are traits and functional traits

trait: well-defined, measurable, property of organisms, usually measured at indiv. level, used comparatively across species

func trait: trait that strongly affects organism performance

Distinguish between environmental filtering and limiting similarity

env filtering: tolerant to local abiotic conditions

env limiting: fitness in local biotic and abiotic conditions

What are response and effect traits and how do they mediate community responses to env change and effects on ecosystem functioning?

response trait: traits in response to changes in ecosystem functioning, may encompass direct response to env change and thru compensatory dynamics in response to changes in sp interactions

effect trait: mediate how organisms affect community and ecosystem, have an impact on ecosystem functioning

community

assc of pops in a given space and time

assemblage

assc of pops in given space and time for a specific taxonomic group

Sink web

all of the feeding relationships that lead to the top pred/consumer of intereste

source web

all feeding relations that arise from a single food source

green food webs

autotroph based/above ground

brown food webs

detritus based/underground

trophic level

level at which organism resides in trophic network

trophic position

position that organism is in the trophic network, can change due to omnivory

networks consist of

links (interactions) nodes (organisms)

nodes often

aggregated (more than one pop)

links

• challenging to quantify

• ingested vs assimilated

• temp variable

• strong v weak important

network topology

structural arrangement of species (nodes) and their interactions (links)

trophic whale

really big thing eating really small things

body size in food web

• optimal foraging theory supports

• not always the case, many pred eat prey bigger than themselves

• trophic whales

food web structure

• not all nodes and links are equal

  • FEW STRONG MANY WEAK

Keystone species

heterotrophs whose effect on community is disproportionately large rela to their biomass or abundance

Dominant species

autotrophs that have large effects in communitites due to high biomass or abundance

Foundation species

• distinguished by their uniqueness

• numerically abundant, account for most biomass in ecosys

  • occur near or at base of network

mutualistic networks

• bipartite networks (2 parts)

• FEW STRONG MANY WEAK

• high nestedness, moderate modularity, low connectance

complexity

# of species (nodes) in a net

stability

dynamics in pop abund. and/or resistnace of network topology to change

Elton (1927)

smple comm. have greater fluctuations in abund. and are less resistant to invasions

May (1973)

increasing complexity decreased stability of theoretical networks with random interaction strengths

McCand and Ronney

Numerous weak interactions decreased stability of theoretical networks with random interaction strengths

nestedness

type of interactions structure where generalists form a core of interacting species and specilalists interact with generalist

connectance

# of links in network, expressed as prop of total # of possible links in network

Modularity

exists in a network when groups of species interact more among themselves then with species from other groups

mutualistic v trophic networks

mutualistic have higher nestedness and connectance but lower modularity

3 factors controlling tot. abund. of organisms at diff trophic levels

1. in absence of higher-level predation, carnivores should be limited by comp for their food

2. herbivore pops should be held below their carrying capacity by carnivores and have little impact on their food

3. in absence of control by herbivores, plants should be dense and limited by comp

rel. importance pred v comp

• Errington - prey po size driven by comp for pred free space

• HSS (1960) - “Green world hypothesis”

  • effect of predation and comp are pronounced at diff trophic levles

  • carnivores most affected by comp

  • herbiv. most affected by predation

  • producers most affected by comp.

trophic cascade

non-adj. trophic level affects the abund./biomass of a lower trophic level

Problems with HSS

• xcess food supply for herbiv. is apparent, not real

• other factors can limit pop, such as habitat avail., env. dynamics, disease, etc

• very simple depiction of food web

Fretwell (1977)

describes effects in communites with diff number sof trophic levels as a function of potential primary productiv.

even food chain length

prod affected by predation

odd food chain length

prod affected by comp.

Oksanen

developed model of equil biomass across trophic levels as a function of poten. primary productivity and using linked consumer-resource pop models

trait-mediated

non-consumptive

density mediated

consumptive

Menge and southerland (1987)

rel. import. model including evn. stress and recruitment intensity

recruitment

addition of additional organisms to the pop/system, increasing comp

food chain length determinants

1. Energy limitation

2. Productive space hypothesis

3. ecosystem type hyp.

4. ecosystem size hyp.

5. dynamic stability hyp.

6. size structure and resource dynamics

energy limitation

• production hyp. - trophic interactions inefficient, FCL limited by avail. energy — more prod. env. support longer food chains

Productive space hyp.

productivity and ecosystem size act tg to determine FCL due to sp. area relationship (SAR)

Ecosystem type hyp.

longer food chains in 3-d vs 2-d ecosystems

Ecosystem size hyp.

FCL increases w/ increasing ecosystem size due to increase in sp. diversity, habitat avail., and heterogeneity

Dynamic stability hyp.

longer theoretical food chiains are less stable therefore disturbance freq of intensity limits FCL

Size structure and resrouce dynamics

rel. import. of energy channels w/ diff. pred-prey size structures

community assembly

process that shapes identities and rel. abund. of sp. within ecological communities (what species, where, and why)

Ideal free distribution (IFD)

sp. occur in rel. abund. to maximize growth; integrates trade-offs in optimal physical env. and comp/predation

assembly rules

sp. can be added to assemblage if certain rules or traits of local assemblage are met

ex. high s-species, tramp sp; persists if arrives earlier, not later

r = ln(Σlxmx)/T

r - intrinsic rate of increase

lx - age-specific survivorship

mx - age-specific fecundity

T - generation time

trait

well defined, measurable, property of organisms, ususally measured at indiv. level, uses comparitively across spceies

function trait

trait that strongly affects organism performance

response trait

many encompass direct response to env change and then compensentory dynamics in response to changes in sp interactions

effect traits

mediate how organisms affect community and ecosystem