why are there so many species in the tropics? (background (processes…
why are there so many species in the tropics?
legacies of past geological, climate, evolutionary
the high latitudes were uninhabitable and inhospitable during the glacial epochs
out of tropics
rates of origination of new species are highest in the tropics
higher rates of speciation than extinction generate high diversity of species and clades within the tropics
most species and clades of tropical origin remain confined to low latitudes, because abiotic environmental constraints inhibit colonization and range expansion out of the tropics
a minority of tropical species overcome these constraints and expand their ranges to colonize and sometimes diversify secondarily at higher latitudes
at these latitudes high rates of extinction result in lower standing stocks of species and clades
cradle and museum
phylogenetic niche conservatism
increasing severity of stress as a filter, resulting in a decreasing number of species and lineages with increasing latitudes
novel adaptive traits are required to tolerate stressful abiotic conditions and expand ranges to higher latitudes
due to long equable environments, most tropical species and lineages cannot tolerate the abiotic stresses at high latitudes - cold and dry
aseasonal climatic regimes have been present throughout most of Earth's history, whereas more extreme conditions, including continental glaciation, have been more intermittent
among these phylogenetically conservative traits are niche attributes , requirements and tolerances for environmental conditions
closely related species tend to share similar traits inherited from their common ancestors
why are rates of speciaton highest in the tropics?
how does variation in speciation and extincion rates and the severity of abiotic conditions across latitudes generate and maintain the standing stocks of species richness seen in the LDGs?
what are the implications of the exceptions, such as the diversification in South America of lineages of placental mammals and cultures of aboriginal humans that colonized the New World relatively via the cold, seasonal environment of the Bering land bridge?
how productivity ultimately limits the total biomass of living matter?
how that biomass is apportioned among the 'number of niche' and hence among species?
how rare species with specialized niches persist in the face of extinction?
increasing from pole to tropics
net primary production (NPP)
limited by temperature(sunlight) and water
limiting the number of individuals per species that could persist in the face of extinction
cannot explain the ubiquity and magnitude of LDG in different organisms and habitats
high species diversity is due to greater 'effective' evolution time (evolution speed) in the tropics, as the result of shorter generation times, faster mutation rate, and faster selection at greater temperatures
how temperature affect
high temperature cause high evolution rate
diversity begets diversity
interspecific ecological interactions
Red Queen coevolution
metabolic theory of ecology (MTE)
species-abundance distributions (SAD)
enemies kill seed or seedling near the parent plant
suppress broad-niche dominant species freeing up resources
because the enemies are host-specific, the more rarer the species are, the more enemies-free space is available
facilitate the persistence of specialized species, allowing them to increase when rare
with decreasing latitude and increasing temperature
similarity in species composition of local community decreases rapidly with increasing distance between sample
the number of species increases more rapidly with increasing sample area
species occupy smaller geographic ranges and a narrower range of aboitic environmental conditions
when thee is an addition of the number of species on an island, the island's immigration rate of new species will decrease while the extinction rate of resident species will increase
increase the island size will lower extinction curves and raise immigration curves