Data Analysis and Mathematical Models

The structure of a community is described in terms of species composition and diversity Communities are comprised of different populations of organisms that interact with each other in negative or positive ways The physical structure of a community is affected by abiotic factors and also the spatial distribution of organisms The mix of species in terms of both the number of individuals and the diversity of the species defines the structure of the community

Predator/prey relationships: Snowshoe Hare and Lynx Changes in hare pop. is followed by similar changes in lynx pop. – predation limits hare pop. and food supply limits lynx pop. Fluctuation cycles are commonly observed between predator and prey

Symbiotic Relationships Mutualism (+,+) Acacia trees provide food & housing for ants; in exchange, resident ants kill any insects or fungi found on the tree and crop veg to increase sun exposure for tree Lichen – algae provide sugar from photosynthesis; fungi provide minerals, water, attachment and protection

Commensalism (+,0) Birds build nests in tree (benefit from protection) the tree gets no benefit or harm Egrets gather around cattle; birds get to eat insects that swarm around cattle; cattle are neither helped or harmed

Parasitism (+,-) Tapeworm live in the digestive tract of animals, stealing nutrients from the host W5Gpk W5Gpk

Introduction of Species Competitive Exclusion occurs when two species compete for exactly the same resources (they occupy the same niche), one is likely to be more successful. One species outcompetes the other and eventually the second species is eliminated from the area ZVw ZVw

Resource Partitioning occurs when species coexist in spite of apparent competition for the same resources Species do this by occupying slightly different niches

Which species of paramecia outcompetes the other? Paramecium aurelia

Physical and biological conditions influence the pace of succession – in both cases, the conditions which make a habitat attractive to resident species may no longer exist, making the habitat more favorable to a new species. Changes include: Substrate texture – change from solid rock, to sand, to fertile soil Soil pH – decrease due to the decomposition of organic matter Soil water potential – ability to retain water varies based on substrate Light availability – full sunlight to partly shady to total shade Crowding – increases with population growth

Occurs on substrates that never previously supported living things. Occurs on volcanic islands, on lava flows, on rock left behind by retreating glaciers The first organisms to colonize a newly exposed habitat are called pioneer species Primary Succession

Rock & Lava 1 st pioneer species is typically lichens; hyphae of fungal component holds onto rock and absorbs moisture; lichen secretes acid which breaks down rock into soil; as soil accumulates more and more species can move in R-selected species will be replaced by K-selected species

Sand Dunes – begins with the appearance of grasses adapted to taking root in shifting sands; grasses stabilize sand to allow for new species to follow Dunes of Lake Michigan are an example

Process begins in habitats where communities were entirely of partially destroyed by some kind of damaging event – this event does not destroy the soil which allows secondary succession to proceed at a faster rate.

Succession on abandoned cropland – begins with the germination of r-selected species from seeds already in the soil; trees follow

Secondary succession of lakes and ponds – begins with a body of water, progresses to a marsh- like state, then a meadow and finally to a climax community of native vegetation.