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Transcript
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 Dominance Yellow-poplar Food webs Keystone species Functional groups • • • • • Feeding level Exploitation of common resources (guilds) Photosynthetic pathway Shade tolerance Life history Physical structure Zonation supratidal intertidal subtidal Association • Relatively consistent species composition • Uniform general appearance • Distribution that is characteristic of a particular habitat Organismic concept of communities Continuum concept of communities Factors controlling community structure Fundamental niche Species interactions Keystone predation Apparent competition Indirect commensalism Top-down vs. bottom-up control 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. Stress tolerance and competition Smooth cordgrass Salt meadow cordgrass Black needle rush Environmental heterogeneity 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. Environmental quality 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: 1. Resilient community: returns to former state after disturbance 2. Resistant community: changes little in response to disturbance Community dynamics: Succession Primary succession Pioneer species Late successional species Secondary succession beach grass shrubs pines oak Primary succession: newly exposed substrate Dryas sp. An early succession species on glacial moraines in Glacier bay. Dryas is a symbiotic N-fixing plant Populus trichocarpa Salix arctica After Dryas, cottonwood and willows become established Alnus incana Alders become the dominant tree after 50 years “Climax”: mixed spruce-hemlock forest Picea sitchensis Tsuga mertensiana Secondary succession: after disturbance Density Autogenic vs. allogenic change Allogenic environmental change Species diversity during succession Oak-pine forest Intermediate disturbance hypothesis Intermediate disturbance hypothesis High Low In New Zealand streams, less disturbed sites support more complex communities (i.e., communities with larger, more connected food webs) Succession of heterotrophs Bark beetle/woodboring beetle Fungi/bacteria Predatory insects Moss and lichen Invertebrates/ mice/ salamanders Changes over geologic time Concept of community revisited Concept of community revisited