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Charles Elton
Mechanisms of Succession
He believed that organisms (including animals) and the environment interact to shape the direction of succession
Diet analysis
Scat analysis
Stable Isotope analysis
Keystone Species
Species that, despite low biomass, exerts strong effects on the structure of the community
Explain Brian Silliman salt marsh experiment
Demonstrated that the decrease in marsh grass was a top-down effect of the overharvesting of blue crab
Paine's keystone species study
Studied Piaster in Mukkah bay
Piaster is a large predator, was removed from experimental plots
Species diversity decreased exponentially within experimental plots
Facilitation Model
The mechanism of succession in which the presence of one species increases the probability that a second species can become established
Isotope
Heavier forms of an element
Dominant Species
Species that have high Biomass and exert strong effects on the structure of a community
Who coined the term Keystone Species
Robert Paine (1969)
Evidence of Facilitation Model
Lupin and gophers on Mt. St. Helens, marine birds on volcanic islands, maram grass on sand dunes
Inhibition Model
A mechanism of succession in which one species decreases the probability that a second species will become established
Stable Isotope Analysis
Examining the isotopic ratios of nitrogen and carbon
Bottom-up Control
Producer biomass is controlled from below, by the availability of resources
How to simplify food webs
Lump taxonomic groups together
Isolate specific parts of the food web
Consider the main trophic levels of the food web
Evidence of Inhibition Model
Seed predation on oaks and pines in the Michigan Sand Dunes
Tolerance Model
The mechanism of succession in which pioneer species neither inhibit nor facilitate the growth of other species
What controls community diversity - Robert Paine
Proposed that the feeding activities of a few species has an inordinate influence on community structure
Top-Down Control
Producer biomass is controlled from above, by the predators
Evidence for Tolerance Model
Gigartina has greatest tolerance for nearshore environment and is tolerant of crab predation
Food Chain
The transfer of energy and chemical resources from its source in producers to herbivores and predators
Paine hypothesis and prediction
Hypothesis - predators increase species diversity
Prediction - predator removal would decrease species diversity
Chain of reasoning - Predators might keep prey species below carrying capacity. Therefore, the potential for competitive exclusion will be low. If predators reduce competitive exclusion, then their predatory activities should increase the number of species that can exist in a community.
Explain Mary Powers' trophic cascades experiment
Cladophora algae in the Eel River, Ca.
Mats of algae fed on by chironomids, which are fed on by predatory insects and two fish species
All fed on by steed head trout
Powers asked if steelhead alter the food web and play a role in the cladophora biomass that occurs in the summer months
When fish are excluded, Cladophora increases. Top-down cascade
Carbon Isotope
Organisms generally have a similar 12C:13C ratio as the food they consumer, with only a slight enrichment of 13C
Progression through seral stages is associated with an ___ in species richness
Increase