Community ecology Outline: • Community structure: attributes • Factors influencing the structure of communities • Community dynamics Chapter 16-18
Community attributes • # of species • Relative abundance of species • Nature of species interactions (food webs) • Physical structure
Community structure • Species richness (# of species within community) 10
Community structure • Relative abundance (% each species contributes to the total number of individuals)
Stand one Stand two
Simpson’s diversity index • D = 0 - 1 • 0: high diversity • 1: low diversity • Stand one (Table 16.1): D=0.13 • Stand two (Table 16.2): D=0.36
Functional groups • Feeding level • Exploitation of common resources (guilds) • Photosynthetic pathway • Shade tolerance • Life history
supratidal intertidal subtidal
Association • Relatively consistent species composition • Uniform general appearance • Distribution that is characteristic of a particular habitat
The number of trophic levels regulates plant, herbivore and carnivore numbers # trophic levels: B/comp: numbers limited by availability of resources (bottom-up regulation). Competition strong, predation weak. T/pred: numbers limited by predation (top-down regulation). Competition weak, predation strong.
Black needle rush Salt meadow cordgrass Smooth cordgrass
Relationship between the number of plants per 300m2 plot beside the hood river, NWT, and an index (ranging from 0 to 1) of spatial heterogeneity in abiotic factors associated with topography and soil. More spatially heterogeneous plots had higher species richness.
Plant species diversity in a control plot and a fertilized plot in the Parkgrass experiment in Rothamstead, England. Fertilized plots have lower species diversity. The Parkgrass experiment, which began in 1856, is the longest running ecological experiment.
Community stability Types of stability: • Resilient community: returns to former state after disturbance • Resistant community: changes little in response to disturbance
Community dynamics: Succession
Primary succession Pioneer species Late successional species
beach grass shrubs pines oak