Laserfiche WebLink
<br /> <br />SOULI:' I CHAPTER 9 <br />THRESHOLDS FOR SURVIVAL <br /> <br />FISH (lake) Lake Lanao <br />AMPHIBIANS Jamaica <br /> <br />FISH (river) <br /> <br />SMALL <br />MAMMALS <br />HIGHER <br />PLANTS <br />BIRDS AND <br />LARGE <br />MAMMALS <br /> <br /> <br />Madagascar <br /> <br />REPTILES Jamaica <br /> <br />Ceylon <br /> <br />Luzon, Cuba <br /> <br />New Caledonia <br /> <br />Yellowstone National Park <br /> <br />100 <br /> <br />500 / <br /> <br />200 <br /> <br />300 <br /> <br />400 <br /> <br />AREA(1,OOO km2) <br /> <br />FIGURE 4. Above: Smallest islands on which autochthonous speciation is <br />known to have occurred for various taxa. Below: Three large nature <br />reserves for comparison. <br /> <br />than do small or sedentary organisms; Note that, roughly speaking, as <br />absolute vagility increases, so does the size of the landmass necessary for <br />apparent autochthonous speciation. Also note that the largest national <br />parks in the world would seem to be too small for the speciation of higher <br />plants, birds and mammals. <br />Not only are the islands in Figure 4 large, they are also old. New Cale- <br />donia and Madagascar, for example, are. ancient islands, being remnants <br />of the breakup of Gondwanaland. Therefore, it would appear that the <br />element of time is also a factor in the production of endemic radiations. <br />Although the data are strongly suggestive, one could take exception <br />with the above interpretation. An alternative is that the apparent depen- <br />dence of speciation on area is spurious, and that the actual area-depen- <br />dent process is the longevity of newly arisen species. This is to say that <br />speciation in plants, birds and mammals may actually occur on smaller <br />islands than suggested in Figure 4, but that the turnover or extinction <br />rate (Chapter 6) is so high on these smaller islands that at any given time <br />it is unlikely that there will be more than one species surviving per line- <br />age. In other words, extinction rate, not speciation rate, is the area- <br />related factor. (Note that Wilcox in Chapter 6 presents biogeographic <br /> <br />600 <br /> <br />165 <br />