The origins of Neotropical amphibian biodiversityJohn J. WiensDepartment of Ecology and EvolutionStony Brook UniversityStony Brook, New York, U.S.A

Why is biodiversity higher in the tropics?From Global Amphibian Assessment (2004)Global Patterns of Amphibian Diversity

from Francis and Currie (2003; Am. Nat.)Patterns of species richness

What environmental variables are correlated with high species richness?

Variables typically climatic (temperature, rainfall) or closely related (energy, productivity)

Patterns of species richness Environmental variables alone cannot directly explain patterns of species richness

Ultimately, species richness patterns must be explained by processes that directly change number of species

Speciation(add species to region)Extinction(subtract species from region)Dispersal(add species to region)(subtract species from region)Number of species in region

SpeciationExtinctionTropical RegionsTemperateRegionsSpeciationExtinctionDispersalUnderlying causes of high tropical diversity

SpeciationExtinctionTropical RegionsTemperateRegionsSpeciationExtinctionDispersalClimate and related factors

Why more species in the tropics?Two general explanations:

1) Diverse clades originate in tropics, disperse to temperate zone recently and infrequently, leaving less time for speciation to build up richness in temperate zone

2) Faster rate of diversification (speciation - extinction) in tropical clades (e.g., rapid tropical speciation, more temperate extinction)

SpeciationExtinctionTropical RegionsTemperateRegionsSpeciationExtinctiondispersalClimate limits dispersal fromtropical to temperate regionsIf clade originates in tropics, can have more tropical richness through more time for speciation,not differences in rates of speciation and extinctionbetween regions

SpeciationExtinctionTropical RegionsTemperateRegionsSpeciationExtinctionDispersalTropical environmental conditions lead to more speciation or less extinction (higher diversification rate)

Two stories about tropical diversity in amphibians What explains patterns of local species richness?(Causes of local richness patterns in treefrogs, Hylidae)

For clades that show faster tropical diversification, what is it about tropical environments that causes this pattern?(Correlates of high diversification in salamanders, Plethodontidae)

Treefrogs (family Hylidae)

Santa Cecilia, Ecuador= 36Cuzco Amazonico, Peru = 31Boriacea, Brazil = 26Savannah River Ecology Lab = 12La Selva, Cost Rica = 12Palenque, Ecuador = 10Phylogenies becoming used to study large-scale richness patterns and local community structure, but not local richness Hylids show extreme variation in local diversity with more species in some sites in Amazonia than in all of Europe and Asia Hylid diversity correlates with overall anuran diversity Hylid Local Diversity

Built new, time calibrated phylogeny for ~362 hylid species (with BEAST) Obtained data on local diversity and climate for 123 sites (but focused on 12 localities representing major regions) What explains local diversity? (climate? time? traits?) Do sympatric clades constrain each others diversification? Hylid Local Diversity

Santa Cecilia, Ecuador= 36Cuzco Amazonico, Peru = 31Boriacea, Brazil = 26Savannah River Ecology Lab = 12La Selva, Cost Rica = 12Palenque, Ecuador = 10Hylid Local DiversityWeak relationships between local diversity and climate across regionsWiens, Pyron, and Moen (Ecol. Lett. in revision)r2 = 0.345P = 0.04r2 = 0.103P = 0.30

Wiens, Pyron, and Moen (Ecol. Lett. in revision)Hylid Local Diversity Strong relationship between local diversity and how long clades have been present in region (using LAGRANGE) r2 = 0.705P = 0.001

Higher local diversity in allopatric cladesP = 0.04P = 0.04Higher diversification rate in allopatric clades

Hylid Local DiversityRange of species body sizes is greaterin more diverse communities(in the tropics)High local diversityassociated with many speciesin same body size classesr2 = 0.431P < 0.001Wiens, Pyron, and Moen (Ecol. Lett. in revision)Rates of body-size evolution arehigher in allopatric clades (P = 0.04)

Treefrog Implications Time (and phylogeny) are important in explaining patterns of local-scale species richness, including high local diversity of Amazonia

Sympatry between clades may slow rate of species diversification, but does not prevent accumulation of species richness over time

Similarly, species interactions (clade sympatry) slows rate of body-size evolution, but does not prevent co-existence of species withi similar body size

Two stories about tropical diversity in amphibians What explains patterns of local species richness?(Causes of local richness patterns in treefrogs, Hylidae)

For clades that show faster tropical diversification, what is it about tropical environments that causes this pattern?(Correlates of high diversification in salamanders, Plethodontidae)

Frogs and Tropical Diversification Many basal anuran families primarily temperate (e.g., ascaphids, discoglossids, pelobatids)

Most anurans (96%) belong to single clade (Neobatrachia) centered in tropical regions

Global diversity patterns dominated by higher diversification rate in tropics? Pipoidea (31 species)Ascaphidae (6 species)Discoglossoidea (22 species)Pelobatoidea (145 species)Neobatrachia (5,149 species)Temperate ascaphidTropical dendrobatid

100200SooglossidaeAscaphidaePipoideaBombinatoridaeRanoideaHeleophrynidaePelobatoidea0Millions of years agoAnurans

Reconstructed phylogeny and divergence dates

RAG-1 data for 84 species (almost all families)

Penalized likelihood analysis (10 fossil calibration points)

Estimated diversification rates for 15 clades

temperatetropicalHyloideaDiscoglossidaeMegophryidaeCaudiverberaMyobatrachidaeLeiopelmatidaeNeobatrachiaWiens (2007, Am. Nat.)

Diversification rate and latitudeStrong relationship betweendiversification rate and latitude in anuransWiens (2007, Am. Nat.)

9 of 10 salamander families primarily temperate

One clade in one subfamily (bolitoglossine plethodontids) is tropical--but contains nearly half of all salamander species

Global diversity patterns dominated by higher diversification rate in tropics?

Diversification rate = speciation - extinction

Temperate ambystomatid

Tropical plethodontidSalamanders and Tropical Diversification

100200Tropical bolitoglossinesSalamandridaeCryptobranchidaeHynobiidaeDicamptodontidaeProteidaeAmphiumidaeAmbystomatidaePlethodontidaeSirenidaeRhyacotritonidae0Millions of years agoSalamanders

Reconstructed phylogeny and divergence dates

RAG-1 data for 66 species (all families)

Penalized likelihood analysis (11 fossil calibration points)

Estimated diversification rates for 12 clades

temperatetropicalWiens (2007, Am. Nat.)

Diversification rate and latitudeStrong relationship betweendiversification rate and latitude in salamandersWiens (2007, Am. Nat.)

Why are diversification rates higher in tropical clades? Many studies have shown faster diversification rates in tropical clades, including studies in butterflies (Cardillo et al. 2005), birds (Ricklefs 2006), and plants (Jansson & Davies 2008; Svenning et al. 2008)

Little known about why tropical clades have faster rates (many hypotheses, few empirical tests)

We used plethodontid salamanders as model system to address the why

Why are diversification rates higher in tropical clades?

Built time-calibrated phylogeny for 250 plethodontid species

Obtained GIS-based climatic data for all 250 species, did PCA on 19 climatic variables, used PCs 13

Divided into 15 clades, estimated rates of diversification and climatic-niche evolution (with Brownie) for each cladeKozak and Wiens (2010, Ecol. Lett.)NeotropicsE North Am.W North Am.

Why are diversification rates higher in tropical clades? Strong relationship between rate of climatic-niche evolution and rate of diversification

Tropical clades have higher rates of diversification and higher rates of climatic-niche evolution

Clades that are geographically isolated have higher rates of niche evolution (e.g., subgenus Eladinea of Bolitoglossa, only radiation in Andes)Kozak and Wiens (2010, Ecol. Lett.)From PGLS, P = 0.008

Salamander Implications In plethodontids, high tropical diversification rates are associated with high rates of climatic-niche evolution, not particular climatic conditions

Limited temperature seasonality in tropics may lead to greater climatic differences between species at different elevations (Janzen 1967)

Faster rate of climatic niche evolution in isolated clades suggests that species interactions are important in driving niche conservatism

Climatic Niche ConservatismClimatic niche conservatism: retention of similar climatic distributions over time, may be relevant to:

Adaptation (or not) to global warming

Distribution of invasive species

Allopatric speciation

Large-scale biogeography of clades (and species richness)

Spread of human agricultural species (and human history)

Why is biodiversity higher in the tropics?From Global Amphibian Assessment (2004)Global Patterns of Amphibian DiversityConclusions:

Both time and rates of diversification are important in explaining high tropical diversity (but at different scales)

Relationship between causes of diversity and climate is not simple

Species interactions are important, but in constraining evolutionary change, not driving it

Main Collaborators Hylid local diversity: Alex Pyron, Dan Moen

Climatic niches and diversification: Ken KozakAcknowledgmentsFunding National Science Foundation: AToL, Systematic Biology

Gracias!Obrigado!Thank you!