There are often in ecology multiple explanations for

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There are often in ecology multiple explanations for a single phenomenon. Could this explanation apply to moths? Class? 3. Trophy hunting decreases body and horn size in bighorn sheep. Male bighorn sheep fight one another to gain access to females. Slide of Fig. 6.1 from text Both larger body size and larger horn size are advantageous in these encounters so are selected for. But when human hunters began shooting these animals, body size and horn size decreased (over a 30-year period). Slide of Fig. 6.2 from text Why? Because human hunters wanted the biggest males and biggest horns as trophies. Why don’t they just shoot them all? – see textbook.
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4. Life history characteristics of fish . North Atlantic cod fishery has collapsed and now a moratorium. Recent study by Olsen et al (2004) shows that this was caused by very intense fishing. Slide. The intense fishing gradually selected for an earlier age/smaller size at which fish mature. We will see why these particular changes occurred later in the course. Reznick recently did experiments with guppies, introducing those from predator-free environments into environments that had large predators and vice versa (here the predators were other fish, not fishermen). Same changes, also more and smaller offspring. When Reznick changed back the environment, the guppy traits shifted back. So here are rapid changes that are genetically based. class – is the selective mechanism here the same as in #3? 5. Rapid evolution and speciation in trout . Another example from fish. There are two kinds of trout – steelhead and rainbow – that are variants of the same species Oncorhynchus mykiss , the former being migratory and the latter stationary Slide . Just discovered (Pease et al. 2009). A rainbow trout population above a river-barrier waterfall evolved from a steelhead introduction in c1910, and fish that got back over the falls are reproductively isolated from the ancestral steelhead, thereby being a sensational case not only of rapid evolution but of rapid speciation!
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