1 Ecological Communities: Change & Balance

2 Ecological Niche Ecological Niche - Description of the role a species plays in a biological community, or the total set of environmental factors that determines species distribution.  Generalists - Broad niche  Specialists - Narrow niche

3 Ecological Niche Fundamental Niche - Full range of resources or habitat a species could exploit if there were no competition with other species. Realized Niche - Resources or habitat a species actually uses.

4 Competition Intraspecific - Competition among members of the same species.  influences which individuals are successful Interspecific - Competition between members of different species.  influences which species are successful

5 Resource Partitioning

6 Resource Partitioning (Realized Niche) Law of Competitive Exclusion - No two species will occupy the same niche and compete for exactly the same resources for an extended period of time.  One will either become locally extinct, or partition the resource and utilize a sub-set of the same resource. Interactions among species are added to regulation by each species’ response to the physical environment

7 Other limits to success: eating your neighbor A predator or parasite or herbivore is an organism that feeds directly upon another living organism  Reduces competition, population overgrowth, and stimulates natural selection.

8 Keystone Species Keystone Species - A species or group of species whose impact on its community or ecosystem is much larger and more influential than would be expected from mere abundance (or biomass).  Wolves, browsers, and vegetation  Starfish, intertidal animals, algae  Beavers, aquatic communities

9 Ecosystems are dynamic, changing “Habitats” are defined by the dominant organisms, the populations of which can rise or fall Changes can be driven by altering the physical environment (promoting species with niches appropriate for the change) Changes can be driven biologically by altered interactions among species

10 “Habitats” are dynamic in space & time Edge Effects – Areas between different habitats can be important to species success  Ecotones can be refuges or areas of high productivity

11 The composition of communities varies from place to place Each species has its own fundamental niche, rarely perfectly correlated with any other species e.g., “beech-maple” forests in Ohio and Pennsylvania will have different sets of species overall Given this “uniqueness” would we have to conserve every beech-maple forest?

12 Communities change through time Ecological Succession  Primary Succession - A community begins to develop on a site previously unoccupied by living organisms. - Pioneer Species  Secondary Succession - An existing community is disrupted and a new one subsequently develops at the site.

13 Primary Succession

14 Ecological Succession Ecological Development - Process of environmental modification (facilitation) by organisms. Climax Community - Community that develops and seemingly resists further change (reached in ~400 yrs for some forests). BUT, over long periods of time, climates change (e.g., glaciers in Ohio 15,000 years bp)

15 How do we deal with complexity? Numbers of components involved Indirect effects (“domino effects”) Complex feedback systems Gradients in  distributions of species  degrees of influence  change through time