Zoology101: Animal Biology Last Lecture Outline Lecture 41 1. Species interactions continued2. NicheCurrent Lecture 1. Community ecology2. Diversity Community Ecology• Food webs ◦ What controls primary production (growth of plants and algae) ▪ Nutrients (nitrogen and phosphorus)▪ grazing by zooplankton ◦ Trophic cascades: indirect effect of top predators on lower trophic levels • Species with a large impact ◦ Dominant species: exert some level of control over the occurrence and distribution of other species, most abundant or have highest biomass ◦ Keystone species: in contrast to dominant species, keystone species are not necessarily most abundant in a community • ecosystem engineers influence other species by physically altering environment • General point:◦ food webs, species interactions, trophic cascades, all emphasize connections, networks among species -both direct and indirect (unexpected and expected)Diversity• Biodiversity: variety of all life forms, all different plants, animals, microbs, their genes, and ecosystems in which they are a part of• Species richness: total number of species in a given community • Evenness: distribution of individuals among the different species • Patterns of species diversity ◦ habitat size (species-area curves)◦ Poles → tropics • Biodiversity crisis ◦ current rates of extinction are unusually high ▪ humans increased extinction rate by 1000 times ▪ 10-30% of mammels, birds, and amphibian species threatened with extinction • Mutational Meltdown and the extinction vortex◦ positive feedback system; small populations tend to get even smaller ◦ can intervention help stop the meltdown?▪ Yes in some cases: genetic rescue in small populations• Causes for modern extinction◦ habitat destruction (loss, fragmentation)◦ Introduced species ◦ Overexploitation• Introduced/exotic species ◦ species introduced to an area outside of their native range ◦ invaders can alter habitat, directly reduced/displace native species (competition, predation), alter ecosystem
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