Many small native fish of southwestern us had a

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- Many small native fish of southwestern US had a geographic ranges reduced completely extinction of some local populations – introduction of large predatory game fish - Introduction of the Nile perch into Africa’s Rift Valley Lakes extinction of ~300 endemic species of cichlids - Introduced parasites also issue – lake trout widely distributed and abundant species , but not adapted to lampreys which are external parasites - Niagara falls formerly prevented Welland Canal enabled Petromyzon to colonize upper Great Lakes
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- On a whole – very little evidence that predators control the broad geographic range limits of prey species 1. Stenophagus predators may be dependant on the abundance of a single prey species a. But if predation pressure intensifies, population size of prey will increase – predator population decline due to starvation and decreased fertility b. If predator pressure is relieved, population of prey will increase – prey population increase feeds more predators due to abundance of prey c. We expect stenophagous predator populations and their prey species to undergo periodic fluctuations in population size – Lotka-Volterra model d. But recent experiments show hare populations fluctuate when predators are excluded – food supply variation results in periodic cycles – echoing the hare- plant cycle. More moose than wolves! - Disease (moose tick) - Food sources also in decline - Complex system Symbiosis: Mutualism, Commensalism, Parasitism and Mimicry Symbiosis – close association between two species that general develops through coevolution - Often the association is necessary for survival of one or both species - Obligatory nature of relationship means there is biological control on geographic distribution of one or both species - Different types of symbiosis Mutualism – close interaction of different species benefits both species Commensalism – benefits one species and has no impact on the other Mutualism - Plant – pollinator relationships - Pollinating relationships can have tight control over geographic distributions of organisms Facultative mutualism- species do better when other species around (more common)(bird/fruit) - Reef building organisms in corals – members or class Anthozoa (related to sea anemones) – intimate mutualism – obligate mutualism - Tough outer skeletons (calcium) carbonate) – generally have coralline algae in tissue – protect algae and get photosynthate – require identical Commensalism - One benefits, other not influenced (eg. Cattle stir up insects for birds; epiphyte orchids) Parasitism - One species benefits at the expense of the other - Parasites dependant on other organisms for nutrients – also often microhabitat - Do not immediately kill their hosts - Majority of parasites are restricted to one host species – some view it as a form of predation - Microparasites: viruses, bacteria and protozoa
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- Macroparasites: parasitic worms, ticks, fleas, lice and mites Eg the forest of North America – the indian pipe – small white plant lacks
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