Understanding why there are so many kinds of tropical trees requires learning, not only how tree species coexist, but what factors drive tree speciation and what governs a tree clade's diversification rate. Many report that hybrid sterility evolves very slowly between separated tree populations. If so, tree species rarely originate by splitting of large populations. Instead, they begin with few trees. The few studies available suggest that reproductive isolation between plant populations usually results from selection driven by lowered fitness of hybrids: speciation is usually a response to a "niche opportunity." Using Hubbell's neutral theory of forest dynamics as a null hypothesis, we show that if new tree species begin as small populations, species that are now common must have spread more quickly than chance allows. Therefore, most tree species have some setting in which they can increase when rare. Trees face trade-offs in suitability for different microhabitats, different-sized clearings, different soils and climates, and resistance to different pests. These trade-offs underlie the mechanisms maintaining alpha-diversity and species turnover. Disturbance and microhabitat specialization appear insufficient to maintain alpha-diversiry of tropical trees, although they may maintain tree diversity north of Mexico or in northern Europe. Many studies show that where trees grow readily, tree diversity is higher and temperature and rainfall are less seasonal. The few data available suggest that pest pressure is higher, maintaining higher tree diversity, where winter is absent. Tree a-diversiry is also higher in regions with more tree species, which tend to be larger, free for a longer time from major shifts of climate, or in the tropics, where there are more opportunities for local coexistence.
机构:
City Univ New York, Biol Program, Grad Ctr, Plant Sci Subprogram, New York, NY 10016 USACity Univ New York, Biol Program, Grad Ctr, Plant Sci Subprogram, New York, NY 10016 USA
机构:
Massey Univ, Sch People Environm & Planning, Geog Programme, Palmerston North 4442, New ZealandMassey Univ, Sch People Environm & Planning, Geog Programme, Palmerston North 4442, New Zealand
机构:
Univ Nacl Comahue INIBIOMA CONICET, Ctr Reg Univ Bariloche, Lab Ecotono, RA-8400 San Carlos De Bariloche, Rio Negro, ArgentinaUniv Nacl Comahue INIBIOMA CONICET, Ctr Reg Univ Bariloche, Lab Ecotono, RA-8400 San Carlos De Bariloche, Rio Negro, Argentina
Ruggiero, Adriana
Hawkins, Bradford A.
论文数: 0引用数: 0
h-index: 0
机构:
Univ Calif Irvine, Dept Ecol & Evolutionary Biol, Irvine, CA 92697 USAUniv Nacl Comahue INIBIOMA CONICET, Ctr Reg Univ Bariloche, Lab Ecotono, RA-8400 San Carlos De Bariloche, Rio Negro, Argentina