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

AmphibiansLizardsSnakes

Moss

BivalvesAnts

LizardsBirds

Marine Gastropods

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

a. ENERGY – DIVERSITY HYPOTHESIS

PET = amount of water that a plant would lose to the environment; increases with radiation and decreases with increasing humidity.

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

"Bottom-Up" - more Energy, more sp. "Top-Down" - 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

Rohde, K Latitudinal Gradients in Species Diversity: The Search for the Primary Cause. Oikos 65: 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 The Latitudinal Gradient in Recent Speciation and Extinction Rates of Birds and Mammals. Science 315: Compared pairs of sister bird and mammal taxa in the tropics and temperate zone. Compared DNA, and estimated time since divergence for these pairs. Temperate pairs of birds and mammals had MORE RECENT divergence times than pairs of tropical species.

BIRDSMAMMALS Time since divergence of species pairs. Age of intraspecific haplotype variation. Age of deepest phylogroup splits all relationships are strongly significant (p < 0.001)....

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

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

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 c. 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? Diversity Disturbance Competitive exclusion in very stable habitats

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

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

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. Intermediate disturbance hypothesis d. 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...