Community Ecology Interactions of a community: interactions that affect survival and drive evolution – Competition - negative effect on both species – interspecific competition - 2 species compete for the same resource – niche - an organisms use of the abiotic and biotic resources in its environment – exclusion principle states that 2 species cannot occupy the same niche Predation - benefits one and has a negative effect on the other – drives evolution - mimicry and other diverse adaptations Parasitism - parasite benefits while the host is harmed – can exert a substantial influence on a population Disease - similar to parasite Mutualism - benefits both Commensalism - one is benefited while the other is unaffected – very rare in nature Interspecific interactions and adaptation – drives coevolution and adaptation of species living in close proximity to each other

Flow of Energy Trophic structure - food chains – size is limited to the inefficiency of the transfer of energy – shorter chains are generally more stable than longer ones bottom up control - producers determine the amount of herbivores which determines the amount of carnivores that can be supported top down control - predators control herbivores which have an impact on the producers

Influence of Species Species with a large impact on community structure – dominant species - most abundant species – keystone species - exert a strong influence despite small numbers – founding species - exert an influence through changing the physical environment

Disturbances influence community structure moderate levels of disturbances can create more species diversity than a high level of disturbance – Storm, fire, flood Alters resources and removes members of species Disturbance is below the threshold for most of the species living in that area human disturbances usually lead to less species diversity – Reduction and alteration of habitat leading to loss of species

Ecological Succession primary succession begins where there is no soil after a major disturbance where soil is left...secondary succession is the 1st level – succession continues until a climax community is established Lichens and mosses create soil from rock through chemical weathering – Autotrophic prokaryotes Grasses and herbaceous plants add to the litter and humus of the developing soil adding nutrients and water holding capacity – Attract animal species that further add to the fertility of the soil – Early species arrival of shrubs and bushes either add or detract to the arrival of the late species (trees) The climax community is stable