BIODIVERSITY V Biodiversity Patterns and Processes A The

BIODIVERSITY

V. Biodiversity: Patterns and Processes A. The Species-Area Relationship B. The Latitudinal Trend in Diversity 1. The patterns

Amphibians Lizards Snakes

Moss

Bivalves Ants

Lizards Birds

Community Ecology I. Introduction II. Multispecies Interactions with a Trophic Level III. Multispecies Interactions across Trophic Levels IV. Succession V. Biodiversity: Patterns and Processes A. The Species-Area Relationship B. The Latitudinal Trend in Diversity 1. The patterns 2. Potential Causes a. energy-diversity hypothesis

"Bottom-Up" - more Energy, more sp. - quantitative effects

"Bottom-Up" - more Energy, more sp. - quantitative effects

"Bottom-Up" - more Energy, more sp. - qualitative effects: energy increasing types of diversity The tropics not only have MORE productivity, they have more KINDS of productivity – more types of plants, allowing greater specialization by more types of animals. We tend to see this diversity evolving by sister species using slightly different resources. This should make sense; sister species are probably very similar, and so they would have to partition some important resources in order to coexist without competitive exclusion.

This diversity evolves by sister species using slightly different resources. This should make sense; sister species are probably very similar, and so they would have to partition some important resources in order to coexist without competitive exclusion.

"Bottom-Up" - more Energy, more sp. "Top-Down" – more energy, more predators, less, competitive exclusion at each trophic level.

"Bottom-Up" - more Energy, more sp. "Top-Down" - more predators, less competitive exclusion. "Faster Evolution" and speciation

"Faster Evolution" and speciation Rohde, K. 1992. Latitudinal Gradients in Species Diversity: The Search for the Primary Cause. Oikos 65: 514 -527. Mutation rates are increased by radiation and heat - so mutation rates should be higher in the tropics. . . Confirmed developmental rate is faster at higher temps, so generation time should be shorter. . Confirmed So, with greater variation and more rapid generational turnover, responses to selection (and other evolutionary agents) should be more rapid in the tropics. . . divergence and speciation should be more rapid in the tropics.

"Faster Evolution" and speciation Weir, JT, and D Schluter. 2007. The Latitudinal Gradient in Recent Speciation and Extinction Rates of Birds and Mammals. Science 315: 1574 - 1576. Compared pairs of sister bird and mammal taxa in the tropics and temperate zone. Compared DNA, and estimated time since divergence for these pairs. IF species diversify more rapidly in the tropics, THEN tropical species pairs should have a more recent common ancestor. RESULTS: Temperate pairs of birds and mammals had MORE RECENT divergence times than pairs of tropical species.

BIRDS Time since divergence of species pairs. Age of intraspecific haplotype variation. Age of deepest phylogroup splits all relationships are strongly significant (p < 0. 001). . and contrary to hypothesis? MAMMALS

Community Ecology I. Introduction II. Multispecies Interactions with a Trophic Level III. Multispecies Interactions across Trophic Levels IV. Succession V. Biodiversity: Patterns and Processes A. The Species-Area Relationship B. The Latitudinal Trend in Diversity 1. The patterns 2. Potential Causes a. energy-diversity hypothesis b. habitat heterogeneity – diversity hypothesis

Andes, Equator Rockies, 60 N

V. Biodiversity: Patterns and Processes A. The Species-Area Relationship B. The Latitudinal Trend in Diversity 1. The patterns 2. Potential Causes a. energy-diversity hypothesis b. habitat heterogeneity – diversity hypothesis c. Species – Area effects

- Area Effect - the tropics have more area than similar ecosystems at higher latitudes.

V. Biodiversity: Patterns and Processes A. The Species-Area Relationship B. The Latitudinal Trend in Diversity 1. The patterns 2. Potential Causes a. energy-diversity hypothesis b. habitat heterogeneity – diversity hypothesis c. Species – Area Effects d. Intermediate disturbance hypothesis

Diversity is Maximized at Intermediate Disturbance (Connell, 1978). Diversity Disturbance

- "Disturbance" is removal of biomass. . . - frequency - intensity - areal extent Diversity Disturbance

- Why is diversity maximized in the middle? Competitive exclusion in very stable habitats Diversity Disturbance

- Why is diversity maximized in the middle? No competitive exclusion because disturbance keeps populations low, but doesn't cause extinctions. . lots of colonists coexist. . . Diversity Disturbance

- Why is diversity maximized in the middle? Environment is too harsh; only species that can survive the disturbance persist. . . Diversity Disturbance

V. Biodiversity: Patterns and Processes A. The Species-Area Relationship B. The Latitudinal Trend in Diversity 1. The patterns 2. Potential Causes a. energy-diversity hypothesis b. habitat heterogeneity – diversity hypothesis c. Species – Area Effects d. Intermediate disturbance hypothesis e. Environmental stability hypothesis

end of last glacial - 10, 000 years ago

So temperate regions have not had enough time to exploit all the available niches opened by glacial retreat.

- BUT. . still a global impact on climate. . .

V. Biodiversity: Patterns and Processes A. The Species-Area Relationship B. The Latitudinal Trend in Diversity 1. The patterns 2. Potential Causes a. energy-diversity hypothesis b. habitat heterogeneity – diversity hypothesis c. Species – Area Effects d. Intermediate disturbance hypothesis e. Environmental stability hypothesis 3. Cradle or Museum?

Cradle or museum? David Jablonski, Kaustuv Roy, James W. Valentine. 2006. Out of the Tropics: Evolutionary Dynamics of the Latitudinal Diversity Gradient. Science 314: 102 -106. Diversity is a function of speciation rate, extinction rate, and immigration rate (range expansion into that region). HIGHER SPECIATION RATE LOWER EXTINCTION RATE

Cradle or museum? David Jablonski, Kaustuv Roy, James W. Valentine. 2006. Out of the Tropics: Evolutionary Dynamics of the Latitudinal Diversity Gradient. Science 314: 102 -106. Diversity is a function of speciation rate, extinction rate, and immigration rate (range expansion into that region). "Out of the tropics" model

Cradle or museum? David Jablonski, Kaustuv Roy, James W. Valentine. 2006. Out of the Tropics: Evolutionary Dynamics of the Latitudinal Diversity Gradient. Science 314: 102 -106. Looked at the origin of bivalve taxa (genera) in tropics and beyond Genera first appearing in the Pleistocene (2 mya)

Cradle or museum? David Jablonski, Kaustuv Roy, James W. Valentine. 2006. Out of the Tropics: Evolutionary Dynamics of the Latitudinal Diversity Gradient. Science 314: 102 -106. Looked at the origin of bivalve taxa (genera) in tropics and beyond Genera first appearing in the Pliocene (5 mya)

Cradle or museum? David Jablonski, Kaustuv Roy, James W. Valentine. 2006. Out of the Tropics: Evolutionary Dynamics of the Latitudinal Diversity Gradient. Science 314: 102 -106. Looked at the origin of bivalve taxa (genera) in tropics and beyond Genera first appearing in the Miocene (23 mya)

Cradle or museum? David Jablonski, Kaustuv Roy, James W. Valentine. 2006. Out of the Tropics: Evolutionary Dynamics of the Latitudinal Diversity Gradient. Science 314: 102 -106. SO: The tropics may be both cradle and museum. And that begs the question regarding divergence rates. . . could pairs of species in temperate zone with recent common ancestors have a tropical origin?