Terms and Concepts for Community Ecology

SSWS (lecture 2)

2014 SSWS density dropped 2-4 fold, most juveniles and adults died, biomass dropped 5-11 fold, impacted the whole range of Pisaster

Pycnopodia was affected the most by SSWS, saw a decline at all depths

Consequence

• coralline algae dominates and there is a loss of biodiversity

Possible Outbreak Causes

• og: warm water temp

• other: OA, hypoxia, pathogens, food, stress other than water temp

• recent hypothesis: oxygen depletion caused by microbial activity in boundary layer of water next to skin (suffocation)

but temperature was not a clear indicator of wasting in Oregon

in 2015 unprecedented numbers of recruits occured

• mean body size declined

• based on density populations have recovered (overshot too)

• biomass has not increased (many small not equal to few large)

• recruitment events have destabilized populations

Highly variable scenario and radically different system than what it used to be

predation rate reduced at several sites

restabilization will take >10 years

decreasing dynamics of intertidal meta-ecosystems

Summary

• recovery slow, still not at pre-wasting levels

• declining performance of mussels related to declining phytoplankton

• declining performance of sea stars

Trophic Biotic Interactions

Predation and Grazing

Predation / Grazing

occurs when one interactor kills or reduces the biomass of another through consumption

ex. what causes the lower limit to the mussel bed? predation by sea stars

Predation’s influence on community structure

• can determine lower/upper limits (zonation)

• influences succession

• controls abundances of dominant species

Predation Regime Concepts (lecture 3)

Keystone Species: a single consumer species that has a disproportionately large community effect relative to its abundance

Diffuse Predation: predation impact spread ~evenly across many consumers in a predator “guild” —> per species effects may be small, but total impact is large

• guild is a group of ecologically similar species

Herbivore (Grazer) Effects (lecture 3)

• have unequal effects on abundance of algae

• not much of an effect on variance

Non Trophic Biotic Interactions

Competition and Facilitation

Competition (interspecific) effects (lecture 4)

competition occurs when interacting species mutually reduce survival or other measures of ecological performance through direct interactions such as overgrowth, preemption, or aggressive behavior

• competition for space/food can determine both basal species and mobile species

• can occur at top and bottom of food web

Interspecific competition

between different species

Intraspecific competition

between conspecifics (same species)

Facilitation (lecture 4)

facilitation occurs when interactions increase the abundance, survival or ecological performance of one or both. if both, its mutualism; if just one is benefited, its commensalism

ex. kelp recruits facilitated by coralline algae

• facilitative interactions are important in structuring communites

Interaction Web

Strucutre is a function of both negative and positive interactions

Environmental stress types

Physiological stress or physical stress

• alter (weaken) spp. interactions

• indirect, but stress can also directly influence community structure

• consumers are often most affected by stress but mobility allows them to escape lethal effects

Physiological stress (lecture 5)

occurs when environmental conditions exceed the normal physiological tolerance range of an organism, compromising biochemical and physiological processes necessary for life

Physiological Performance Curve (lecture 5)

shows max performance over increasing environmental stress

Environmental Stress Model (lecture 5)

1. growth is the difference between energy intake and metabolic costs, both of which increase under “no stress” conditions

2. low temperatures are stressful because feeding activity declines non-linerarly, while metabolic rate declines linearly

3. high temperatures are stressful due to thermal interference with physiological functions, which continue to increase while feeding rate (activity) first levels off and then ceases, and then drop to zero with death

Consumer Stress Model (lecture 5)

when not protected from prede=ators, prey do better under increasing stress

Physical stress (lecture 5)

occurs when physical forces (waves, rolling rocks, logs, currents) exceed an organisms normal tolerance range, thereby compromising strength

OA (saturation state) (lecture 6)

lowered saturation states impair calcification

• calcium and CO2 compete for carbonate

hypoxia/anoxia (lecture 6)

deoxygenated waters

• common in human footprint waters (estuaries, terrestrial runoff areas)

Upwelling driven hypoxia

1. decaying plankton consumes o2

2. makes oxygen minimum zone

3. upwelling occurs

4. decaying plankton consumes more o2 and releases more co2

Marine Heat Waves

unusually warm water

Bottom Up Effects (lecture 7)

productivity gradients driven by nutrients and light (primary production)

• flow of energy from bottom of food web to higher trophic levels

Complex interactions (lecture 8)

interactions among three or more species leading to changes such as “indirect effects” — typically not what would be predicted from pairwise species interactions

• Density mediated

  • reduce numbers

• Trait mediated (indirect effects)

  • reduce activity

Direct effects (lecture 8)

predator, herbivore, basal species

• predation and herbivory

• interference competition

• recruitment inhibition

• recruitment facilitation

• feeding inhibition

• habitat provision

Indirect effects (lecture 8)

a chance in abundance, size, or distribution of a species resulting from its interaction with a species that is affected by a third species

• use the sign rule to tell if its a positive or negative indirect effect

• models

  • keystone predation

  • exploitation

  • apparent

  • indirect mutualism

  • indirect commensalism

  • habitat facilitation

  • trophic cascade

• important in food webs

• may generate changes in communities running counterintuitively to expectations based on direct effects alone

apparent competition

increase in prey species b leads to an increase in shared predator a which increases in abundance or size, and preys more heavily on prey species c leading to its decrease

• mechanism is indirect through predator

Generality of Indirect effects (lecture 8)

1. cannot predict species affected without known ALL interactions in web —→ more species = more interactions

2. cannot predict relative importance of direct vs indirect effects from an expirement —> they account for as much as direct

3. changes from indriect effects will be greater than direct effects

4. indrect effects take longer

5. indirect effects from long interaction chains will be greater than those reulting from short interaction chains

Larval Transport (lecture 9)

the movement of larvae from the adult habitat, to the planktonic environment, and back to the adult habitat on the shore or subtidal bottom

Dispersal

the distance from the natal site to the settlement site

Connectivity

dispersal + survival to reproduction

Settlement

point at which an organism first takes up residence on the substratum

Recruitment

the addition of new individuals to the population; i.e. survival of recently settled juveniles for a period of time after settlement

• highly variable

• between ecosystem links

Factors influencing recruitment rate

larval pool, physical transport processes, micro-hydrodynamic, behavioral, and substrate availability processes, biological interactions, disturbance, physiological stresses, flow rates

Larval Transport Mechanisms (lecture 9)

Upwelling/Downwelling/Relaxation

• recruitment in pulses of high settlement then low settlement

Internal Tidal Bores/Waves

• coastal waters are stratified (warmer layer over cooler layer), incoming tides can transport larvae that accumulate at the boundry between layers

Surf Zone Hydrodynamics

• larvae need to get through surf zone to settle

• reflective / dissipative surf zones

Larval Behavior

• model of vertical swimming by larvae to remain near shore

Interactions in the water column

• more predators = less prey able to recruit

Integrated Mechanism

• series of larval transport mechanisms

Dispersal and connectivity (lecture 9)

Limited Dispersal Distance

• settling close to source

Long distance dispersal of Alga

• main transport are gyres and kelp spores/ drift alga

Flow topography effects

• larvae have to pass over/through rocks so few are left when they reach the sheltered region

productivity effects on recruitment (lecture 10)

food makes larvae grow faster

Post Settlement Interaction Effects (lecture 10)

Positive interactions

• more settlement with facilitation

Negative interactions

• limpet bulldozing

• algal whiplash/ barrier

• predation

Climate Change effects on recruitment (lecture 10)

wind effected

Recruitment in structuring communities

low recruitment = similar densities of adults and recruits

• recruitment more important

high recruitment = not similar densities of adults and recruits

• post recruitment factors more important

Lecture 10 Take Home

Between ecosystem links

• variation in recruitment from local to glabal scales may be understandable in relation to processes influencing larvae and spores in the pelagic environment

  • currents, biotic proccesses, food, dispersal, behavior

Settlement in shore

• inital distribution and abundance of settling larvae may be modified by physical and biotic interactions

Recruitment limited populations

• larval supply insufficent to fill adult habitat

Commnity

set of species of species occuring in a particular habitat

food web

species linked by trophic interactions

interaction web

group of strongly interacting species in a food web

interaction strength

magnitude of the impact of species interactions

context-dependance

concept underlying variable interaction strength, communnity dynamics

meta-community

set of local communities linked by dispersal

ecosystem

biological community plus physical and chemical environment

meta-ecosystem

set of ecosystems linked by spatial flows of energy, material, and organisms

Comparative-experimental approach

“cant do experiments at large scales”

• use of identically designed, executed, locally-replicated field experiments at multiple sites within the same habitat type

Single Factor Models (lecture 11)

competition model

• structure of a community is determined by competative interactions (space, food, light)

disturbance model

• strucutre of a community is driven by disturbance either physical or physiological

top down

• determined by predation or grazing, interactions that operaute from the top of the food web down

bottom up

• supply of nutrients or biomass grown by primary producers flowing up food web

Synthetic (Multifactor) Models (lecture 11)

physically modified top down control or environmental stress models

• strucutre of meta communnity is determined in a predictable way by a combination of species interactions and how these are modified by the environmental stress

  • trophic interactions

modified environmental stress model

• structure of a meta community is determined by facilitation as well as other factors discussed earlier

  • facilitation will be strongest at most and least stressful ends of gradient

recruitment/environmental stress model

• depends on rate if recruitment, which determines the strength of predation and competition

  • high recruitment = abundant prey = strong competitoin

  • low recruitment = sparse prey = no competitoin, variable predation and disturbance

recruitment dynamics models

• driven by variation in recruitment interacting with biotic interactions

  • as upwelling strengthens latitudinally from n to s along west coast, recruitment is limited and interactions will weaken

Meta ecosystem model (lecture 12)

strucure of ecological communities depends on: the supply of ecological subsidies, defined as bottom-up inputs (nutrients, producitvity, detritus) and propagule supply

• how these flows strucutre food webs

• feedback loops

intertidal systems are meta ecosystems

Intermittent Upwelling Hypothesis (lecture 12)

upwelling goes back and forth

• peak for phytoplankton, larval retention, responce of prey, predation effect

Lecture 12 Take Home Messages

structure of rocky intertidal communities varies with inputs of ecological subsidies

variation at higher trophic levels due to both mesoscale and macroscale variation in oceanography

important influences at each spatial scale

meta-ecosystem approaches enable understanding of coastal ecosystem dynamics

general model of community and ecosystem dynamics should incorporate species interactions and how these vary with environmental drivers and ecological subsidies

Scale of diversity (lecture 13)

decline in diversity towards poles

• local diversity linerarly related to regional diversity

• poleward local diversity represents an increasing fraction of regional pools

Measurement of Diversity (lecture 13)

you need relative abundance and species richness

• quantified by shannon index and simpson’s

• index

• concept of evenness

Local Scale Diversity (lecture 13)

Predation hypothesis

• species richness in low zone higher because of predation preventing domination

• Intermediate Predation Hypothesis

  • low low = competitive exclusion

  • high low = only defended species survive

• Keystone species concept

intermedeiate disturbance hyothesis

• diversity will be highest where disturbance frequency is intermediate with respoect to recovery ability of the distrubed system, lowest where disturbance frequency is high or low

competition and diversity

• diversity is maintained by non-hierarchal overgrowth competition

facilitation

• positive interactions can theoretically increase diversity by creating conditions allowing species to persist that would otherwise die due to stress or predation

Why care about diversity

aesthetics, practical, evolution, functional

Productivity as a large scale factor affecting diversity (lecture 14)

productivity model

• peak diversity being at the center and lower diversity lower “slopes”

producitvity-stress-diversity model

• check lecture 14 slide 7

Geographic patterns of diversity (lecture 14)

predation intensifies with warmer temperature

Global Diversity

base model= neutral theory — spatially explicit

—> add features (speciation and extinction) and (dispersal and disturbance)

assumes species are ecologically equivalent

abundance is a zero sum game

• number of individuals, species, differet area or different productivity

increasing temperature increases rates of turnover and speciation

Latitudinal diveristy gradient (lecture 14)

strong gradient produced by area/producitivty, turnover and speciation rates

resiliance

capacity of a system to tolerate disturbance without shifting to an alternate state

Community (State variables)

quickly changing

• density

• age

• spatial converage

• biomass

ecosystem (parameters)

slow responders

• birth, death, migration

• carrying capacity

• predation rates

Ball and Cup model (lecture 14)

ball = local community

basin of attraction

3D surface = environment

meta-ecosystems = groups of balls

large perturbations force balls into alternative state