why are there more species in the tropics?
cradle - faster speciation - lower extinction, longer time higher carrying capacity more niches, larger niches larger land surface area.
how much more energy does the tropics get annually compared to the poles?
2.5 x more
what can you model species number by?
function of environmental variables
where is mammalian species richness high?
where its warm, wet and mountainous and where north and south biomes join up
what is the time for speciation hypothesis?
glaciation wiped high lattitudes clean
most tropical regions have been more stable
temperate speciation rates might now be high.
what is niche conservatism?
the tendency of a species to retain aspect of their fundemental niche over time
what does species richness show?
complex spatial patterns, not just longitudinal gradient