Community Ecology Final

Mutualist mediated coexistence

Mutualist mediated coexistence

Two competing plant species have mutualisms with mycorrhizal fungi. Inferior competitor can be excluded, but if the fungus prefers it they can coexist. Depends on what’s present.

Indirect effect

fungi allow plants to exist in areas it couldn’t otherwise, changing the base of the food web. Dominant competitors with reduced performance without mutualism, increasing species richness with weaker competitors doing well.

Stress gradient hypothesis (SGH)

The importance of competition or facilitation interactions differ under different levels of stress. Facilitation more important in stress, competition more important in benign.

RNE (relative neighbour effect)

Measures effects of neighbours on target species

Positive at high elevations: neighbours have positive effect in more stressful environments

Negative at low elevations: neighbours have negative effect in less stressful environments.

Host-parasite web

Food web that focuses on grazers and their resources

Mutualist web

Focus is on interactions the benefit both species

Interaction webs

Includes trophic (vertical) interactions and non-trophic (horizontal) interactions. First level is primary producers (autotrophs), then primary consumers (herbivores), then secondary consumers (carnivores), then tertiary consumers (carnivores/often top predator).

Connectedness

High. Number of observed links in networks, expressed as a proportion of the total number of possible links.

Nestedness

High. Specific type of interaction structure in which species with many interactions (generalist) form a core of interacting species. Specialist normally interacts with generalist and not with each other.

Modularity

Low. Exists when groups of species interact among themselves more than with species from other groups.

Food chains

Transfer of energy and nutrients through trophic levels, each species exists only at one trophic level in chain. Flow originates from autotroph/primary producers, herbivores are primary consumers, secondary and tertiary are the predators and parasites.

Food webs

shows all predator/prey interactions, does not include information about strength of interactions, species can feed at multiple levels at once, many species are omnivores, idealized webs do not include detritivores, symbionts, nor non-trophic interactions like competition. Transfer of energy and nutrients through all tradition predator-prey trophic levels.

Connectedness webs

Structural webs. Shows all trophic interactions between species but not strength. shown as species or guild at higher trophic levels (less to identify). At lower trophic levels, grouped by broad functional groups. Most webs better resolved at higher levels → lower levels are hard to identify to species level, more numerous, and difficult to quantify in terms of trophic relationship. Show all relationships evenly.

Energy flow webs

Measures of amount of energy (biomass) moving between species within a food web. Difficult. Some communities fit energy flow, others do not. Is there importance in the energy flow based on how much flows? Show the thickness of arms.

Green food web

Basal trophic level is autotrophs (fast energy channel)

Brown food web

Basal tropic level is detritus (slow energy channel)

Structural properties

generality (number of species that are prey for a specific predator), vulnerability (numbers of predators a prey species is consumed by).

Functional webs

Focus is on strength of interactions between species within community. Measure strength through removal experiments. Weak interactions are overrepresented in nature and can play a large role in stability food webs.

Parasitoids

Act like parasites at first, but eventually kill their host (so also act like predators)

Parasitic networks

75% of links in food web involve parasitic species and their biomass can exceed an apex predator. Cryptic and rarely included in food webs (except for parasitoids). Rarely kills host, so harder to measure impacts. Can affect host behaviour, influence host mortality rates/rate of E transfer between host and its predator trophic level.

Density-mediated effects

When one species affects a second species through its impact on the abundance of a third species

Trait-mediated effects

When one species affects a second species through its impact on the phenotype of a third species (e.g. changes in behaviour, habitat use, morphology).

Trophic facilitation

When a consumer is indirectly helped by a positive interaction between its prey and another species. Juncus has an indirect effect on aphids in a salt marsh due to its impact on aphid food.

Competitive networks

Interactions among multiple species that interact directly in negative ways (no one species dominates because of indirect effects)

Competitive hierarchies

One species dominates interactions (asymmetrical competition, amensalisms)

Dominant species

Species that have a large effect on a community because it is more numerous or has the highest biomass within that community. Antelope, tree, ants.

Keystone species

Species that affect other members of community in ways that are disproportionate to its abundance/biomass. Beavers, sea otters, and hippos

Foundational species

Species that provide structural habitat for others. Sea otters, trees, coral reefs, kelp, mangrove.

The green world hypothesis

The world is green because herbivores do not control producer biomass. Most producer biomass moves through brown food web after producer dies. Consumers cannot do too much to plants because the things above it is stopping it from doing too much damage.

Panmixia

Individuals freely move around habitat/range, also freely interbreed with other members of species → NO population structure, gene flow is widespread. Species that show this are highly mobile. Good disperser, interbreeding habitat. Move, likely to find mate, not much structure, no genetic isolation, one giant population. Patchy distribution.

Classical metapopulation model

Levins (1970) set of local subpopulations that persist in balance between random local extinctions and establishment of new local populations.

Patches identical, discrete, connected. Occupied or unoccupied. Constant rate of extinction (m). patch colonization rate = cp(1-p) → c is per patch colonization rate

Dispersal limitation

Species is unable to occupy all suitable patches in its environment. This has some important consequences for population dynamics, species coexistence, community structure.

Extinction debt

Delayed extinction that occurs years after critical loss of habitat has occurred

Breakdown of metapopulations because of habitat loss. Isolate populations.

“living dead” - conserving current habitat will have virtually no effect.

Assisted dispersal (assisted colonization, migration)

Involves deliberate movement of species to new suitable area. Species moving risk not establishing, creating an invasive species. Species go and can be restored.

Mainland-island metapopulations

Large population or patch acts as a mainland (lacks sig risk of ext), smaller populations are islands with more risk of extinction (source-sink dynamics)

Patchy populations

Individual within a single interbreeding population are clumped in space, but clumps do not exist as separate populations (high degree of gene flow) (panmixia?)

Nonequilibrium populations

Extinction is not balanced by recolonizations (goes and stays extinct). No gene flow to recolonize or rescue effect. Entire population will go extinct if all local populations disappear. Categorical, variation.

Habitat fragmentation

Can create metapopulation structure. Patches shrink, become more isolated, it’s harder to recolonize. Extinction rate > colonization rate you get non-equilibrium.

Isolation by distance

Patches that are further apart are more isolated, reducing colonization rate. close too much gene flow, far not enough

Casper and Taper model

Interspecific competition, environment gradients, gene flow, and the coevolution of species borders forms a model. Species one and species two have a venn diagram of possible range. Edge populations aren’t happy compared to middle ones (sinks on the outside).

Gene flow between populations is a source/sink dynamic. More individuals = more babies = more immigrants.

Region of sympatry

Sink with a competitor now. Fighting with yourself and others for resources. After secondary contact separates it from adaptive radiation.

Density compensation - greatly impact size of population in zome

Worse competitors may be competitively excluded, undergo character displacement (niche partitioning).

Competition and colonization trade-off - both persist

Fugitive species

Inferior competitor can exist because it is better at colonization (escaping, constantly on the move)

Competition

Resources unlimited: invest little into each offspring and have a lot because offspring are capable of finding their own resources

Resource limited: have a few, large offspring and invest in parental care.

Tolerance / Fecundity Tradeoff

Consider an environment containing multiple patch types (patch heterogeneity). Species can now differ in tolerance of different patch types. Species can differ in possibility of reaching a patch.

Patch-dynamics

Extension of metapopulation model to more than two species. Typical homogeneous patches, dispersal occurs at slower rate than local dynamics. Competition-colonization tradeoffs.

Species sorting

Emphasizes differences in species’ abilities to utilize different patch types in an heterogeneous environment. What if dispersal is perfect for people picking an area and staying. Intermediate dispersal makes patch types preferably reachable. High dispersal → homogenization.

Mass effect

Extension of principles of source-sink dynamics and rescue effects to multiple species. Change in alpha/beta. Heterogeneous patches. Dispersal effects local dynamics.

Neutral metacommunity mechanism-based approach

Assumes species are functionally identical and that niche differences are unimportant. Environment context irrelevant. Species do not vary in demographic rates. Composition mainly related to size of metacommunity.

Assumptions of metacommunity model

1. Each local community contains S species that are competing for limited vacant patch

2. Metacommunity consists of N local communities (heterogeneous)

3. Constant proportion (a) of each local population disperses between communities.

No dispersal

Each local community dominated by best local competitor. alpha diversity low and beta and gamma at maximum.

As dispersal increases

Alpha increases, beta decreases, gamma remains the same.

As dispersal exceeds threshold

alpha decrease, beta slight rise, gamma decline

High level of dispersal

Metacommunity functioning as one large community, best regional competitor exclude other species entirely. All levels of diversity are at their lowest as a result.

Mass effects perspective

Invertebrate diversity varies with pool isolation. Intermediate pool isolation has alpha really high. Higher dispersal potential showed no relationship between species richness and isolation distance. Passive dispersers are boring basically

Regional pool

Colonize tidal zones. Determines local community and how to handle climate change. Things shift and species die. No dispersal → just enough dispersal to stay alive. Species sorting effects are just robust enough for climate change.

Neutral perspective

All species are functionally equivalent (lack of niche, lack of species differences), and have identical per capita birth, mortality, and dispersal rates.

1. Number of individuals in community is constant. Space is limiting and all space is occupied. If one species enter, abundances of other species decline to make room

2. All individuals, regardless of species, have equal probability of colonizing open space.

3. Death occurs at a constant and fixed rate.

Stable coexistence

Species tend to recover from low densities and species densities do not show long term trends. Species abundances vary, but all species persist in area.

Unstable coexistence

Species may coexist within a community for long periods as a result of slow rates of competitive exclusion. No mechanism promoting species recovery. Neutral theory assumes unstable species coexistence (inter and intraspecific competition). Long term diversity maintained through immigrants

Equalizing mechanisms

• Make you equal, neutral approach is relevant here

• On a spectrum, the closer the competitive ability, closer to equalizing/neutral approach. More likely one will be faster.

• Overtime biodiversity goes down, tend to show up in system with regular disturbance

• Intertidal zone and fighting for space: better competitor shows up and stays there until wave comes around and resets.

Stabilizing mechanisms

Favour species recovery when it becomes rare. Reduced fitness difference between them. When you’re common, you’re the target.

Relative nonlinearity of competition

Two or more species can coexist on a single, limiting resource if their functional responses have non-linearity. Resource abundance needs to fluctuate.

Storage effects

Species store effects of good years as a buffer against the impacts of bad years. Storing seeds

Lottery model

Environmental harshness

Extreme habitats typically dominated by an extreme abiotic factor. Special morphologies in species. Low plant productivity. Hard to prove lower species richness in harsh environment.

Successional facilitation

Early successional species modify physical environment in ways that favour invasion by later successional species. Soil and shade.

Successional inhibition

Early arrivals inhibit invasion of later species, but cannot completely prevent their appearance ← slows succession down, but does not stop it. Common around water, later become established through disturbance. (algae)

Successional tolerance

Early colonists make environment less suitable for later successional species. Little to no effect. Really just drives succession.

Successional mosaic model

High levels of biodiversity when it resets. Explains clearings, edging (species didn’t leave, they just jumped around the forest), storage effects (exist as seeds and wait for fire to free things up).

Alternative stable state

Sometimes different communities develop in same area under similar conditions. Human actions can lead to switch alternate state (Eg. coral reef → algal communities)

Regime (phase) shift

A change from one community stat into another state.

Tipping point

A critical threshold that, once reached, will trigger a regime shift in a system

Resistance

The strength of a perturbation needed to cause a regime shift in a system

Resilience

The speed at which a community recovers from a perturbation

Ecological resilience

Largest magnitude of perturbation that a system can handle without undergoing a regime shift

Engineering resilience

The time it takes a system to recover from a perturbation

Hysteresis

Delayed response to forward and backward changes in environmental conditions (e.g. need to reach a tipping point before can change to alternate community).

Wide genotypic variation

Oscillations in prey and predator densities → prey defensive trait variation maintained due to temporal variation in direction of selection and rate of evolution (alternating between selection for defensive ability versus selection for competitive ability over time → balancing selection for both)

Narrow genotypic prey defense variation

Within one predator-prey oscillation, prey evolved to fixation on one moderately well-defended genotype, and predator + prey populations were in equilibrium.

Ecological restoration

Practice of restoring species/ecosystems in an area to a point in time before they were degraded, damaged, or destroyed (theory)

Restoration ecology

Science of ecological restoration, research, scientific study of restored populations, communities, and ecosystems. (practice).

No action, rehabilitation, partial restoration, complete restoration

No action (passive restoration)

Recovery possible without human intervention, or restoration has previously failed or is deemed too expensive.

Rehabilitation

Degraded ecosystem is replaced with a different, productive one (can involve replacement of a few species, or many species).

Partial restoration

At least some of original ecosytsem functions/species are restored (typically, focus is on dominant species, resilient species, keystone species, leaving rare species for later).

Complete restoration

Original ecosystem, complete with species composition/community structure, restored through adaptive restoration, after original cause(s) of loss are mitigated.

Reconciliation ecology

Development of urban places where people and biodiversity can coexist.

• Goal: to find ways to promote and protect biodiversity in human-dominated landscape

• Potential habitats: landfills, city parks, green roofs, privately owned backyards, golf course (ponds or fringe habitats)