why are there so many species in the tropics?

click to edit

background

patterns

LDG

processes

historical

legacies of past geological, climate, evolutionary

the high latitudes were uninhabitable and inhospitable during the glacial epochs

ecological

niche relationship

out of tropics

  1. rates of origination of new species are highest in the tropics
  1. higher rates of speciation than extinction generate high diversity of species and clades within the tropics
  1. 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
  1. a minority of tropical species overcome these constraints and expand their ranges to colonize and sometimes diversify secondarily at higher latitudes
  1. at these latitudes high rates of extinction result in lower standing stocks of species and clades

cradle and museum

niche conservatism

phylogenetic niche conservatism

  1. increasing severity of stress as a filter, resulting in a decreasing number of species and lineages with increasing latitudes
  1. novel adaptive traits are required to tolerate stressful abiotic conditions and expand ranges to higher latitudes
  1. due to long equable environments, most tropical species and lineages cannot tolerate the abiotic stresses at high latitudes - cold and dry
  1. aseasonal climatic regimes have been present throughout most of Earth's history, whereas more extreme conditions, including continental glaciation, have been more intermittent
  1. among these phylogenetically conservative traits are niche attributes , requirements and tolerances for environmental conditions
  1. closely related species tend to share similar traits inherited from their common ancestors

questions

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?

Hutchinson

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?

producticity

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

kinetics

Klaus Rohde

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

mutation rate

selection

shorter generation

high temperature cause high evolution rate

density-dependent relationship

metabolic theory of ecology (MTE)

R=e^(-E/kT)

niches

species-abundance distributions (SAD)

temperature-alpha diversity

diversity begets diversity

interspecific ecological interactions

Red Queen coevolution

Janzen-Connel process

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

spacial relationships

beta diversity

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

species dynamics

island ecology

area-diversity pattern

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