community ECOLOGY EXAM 1

Assemblage

a subset of a community, a group of species, usually of the same taxa, done at the assemblage level becuase studying a whole community is difficult.

Forbes- 1887

“the lake as a microcosm” proposed lakes as a coherent unit. “the balance of nature” Organisms work together to balance the system (population size)

Clements 1916

Agreed with Forbes, plant succession and ecosystem changes. Proposed communities as coherent units. “super organism concept” communities are born, grow, and die like organisms. Directions among species keep species in certain areas, mainly focused on biotic interactions like competition.

Gleason 1926

Individualistic concept- each species has their own requirements and tolerances to survive/ grow. If species occur in the same area together it is because they respond the same way to the environmental gradient (overlap). Species abundance vs env gradient (no transition zones). He focused on abiotic factors.

Elton 1927

Animal ecologist, focused on predator/ prey interactions (food web/ invasion ecology) Proposed that communities have limited membership.

Lotka 1925 and Voltara 1926

Developed equations to describe interactions mainly competition. Showed that when two species compete for the same limited resource they cant co exist.

Gause 1934

Tested Lotka and Voltara models on 2 species of paramecium. Developed the competitive exclusion principle. Hard to apply to diverse communities

Grinnell 1917

Niche is the habitat or ecosystem that an organism can occupy.

Elton 1927

Niche is the role an organism plays in a community, focused on trophic niche.

Gause 1943

Made connections between degree of niche overlap and intensity of competition.

Hutchinson 1957

Proposed a way to quantify niche (n-dimensional hypervolume). Distinguished between fundamental and realized niche

Velland 2010

Conceptual framework of the functioning of community ecology, the black box of community ecology

4 Processes of distribution and abundance

Selection, speciation, drift, and dispersal.

Selection

anything that determines relative success of a species in a community. A determinate ( non random) process result of competition, disease, predation, etc…

Speciation

Evolutionary process creates diversity/ new species

Drift

Stochastic (random) changes in relative abundances, due to chance, leads to random chance of success, common in birds/ bats.

Dispersal

Does not consider migration, refers to movement in or out of local habitats for things like less competition, or more resources. Leads to gene flow/ species persistance.

Whittaker 1960/1972

Proposed diversity can be measured on different spatial scales like alpha, beta, and gamma diversity.

Alpha diversity

represents number of species in a local community/ smaller size area within a habitat.

Beta diversity

A measure of the different species composition between 2 or more habitats within a region.

Gamma diversity

total number of species in a region.

LDG time theory Wallace 1878

The tropics are older and have been habitable for longer since they were not effected by glaciation, they have had more time to accumulate species.

LDG Productivity theory

There is higher energy from the sun which increases primary production, thus increasing total ecosystem productivity and feeding higher trophic levels more effeciently.

Colwell and Hartt 1994

Proposed LDG reflects the outcome of putting species in a bounded domain. Pencil box model.

LDG More individuals hypothesis

The higher primary productivity leads to higher species richness which allows for increased speciation.

LDG tropical niche conservationism theory

Lineages originate in the tropic and stay in the tropics, species lack the flexibility to evolve and adapt to temperate climates.

LDG Evolutionary hypothesis

main focus is on diversification (speciation- extinction) rates

Stebbins 1974

Proposed the tropics are a cradle for the generations of new species and a museum for the preservation of the taxa there. High potential for speciation and low extinction rates= high diversification rates.

Mechanisms of productivity

selected species, niche complementarity, and competition.

Niche complementarity

resource partitioning by different species increases productivity through facilitation and resource partitioning

Nutrient cycling and retention

Niche complementarity increases resource partitioning, which increases SR. This increases resource use and efficiency which decreases nutrient retention.

Exponential model assumptions

1. remove I/E, closed population

2. population growth is constant, time steps are very small

3. constant b/d rates

4. no genetic structure

5. no age structure

Logistic model assumptions

1. b/d are linear

2. closed population

3. no genetic/ age structure

4. continuous growth

5. constant k

Log growth model ( small oscillations)

rT is less than 0.37

Medium product (dampened oscillations)

0.37< rT< 1.57

Large stable cycle

rT>1.57