Transcript Food Webs
Food Webs Food webs are sometimes simplified (conceptually) to the drama of a single predator-prey interaction but, these are the (proverbial) tip of the iceberg. Ecological community interactions are extremely complex… Most food web are extremely complex …and our understanding of virtually all food webs is incomplete Predators, that are NOT directly interacting, but are interacting Herbivores, that are competing, and also prey items Here is the ecological story: In competition, the larger Daphnia will outcompete the smaller Daphnia. The salamanders eat the larger Daphnia, allowing the smaller Daphnia to persist. The midge can ONLY eat the smaller Daphnia. Thus, where the salamander larva is present, the midge larva do well… because they control the population of the midge prey’s competitor. Food web interactions can be: Direct and/or indirect. Acute and/or chronic. Spatially distinct and/or diffuse. Multigenerational and/or unique to a particular moment in time How are communities regulated? Regulation of community structure… Top-down regulation, keystone predators and the trophic cascade Keystone... Pisaster: The quintessential Keystone Predator!? Robert Paine (1969) Removing the starfish resulted in a massive change in the diversity of the system wherein one species crowded out others Regulation of community structure… Top-down regulation, keystone predators and the trophic cascade. Are all different terms for the same effect. Predators control the food web structure through predation. Trophic cascade is particularly, and specifically, focused on the influence of predators controlling food web structure from the top of the food web. Keystone predators Yellowstone wolves control elk populations in two important ways: 1) Elk population numbers are reduced 2) Modify elk behavior The Ecology of Fear http://www.pbs.org/wnet/nature/episodes/in-the-valley-of-the-wolves/video-wolves-on-the-hunt/220/ http://www.pbs.org/wgbh/nova/wolves/lonesome.html Regulation of community structure… Bottom-up regulation… Primary producers drive community structure? Regulation of community structure… Bottom-up regulation… Primary producers drive community structure? Regulation of community structure… Keystone Herbivore? Regulation of community structure… Madagascar Flying Fox: A Keystone Seed Disperser? BeaverA keystone landscape engineer??? Food webs are multifaceted Shall we assume that time stands still? Food Webs