Marcel Cardillo

The delayed rise of present-day mammals

Did the end-Cretaceous mass extinction event, by eliminating non-avian dinosaurs and most of the existing fauna, trigger the evolutionary radiation of present-day mammals? Here we construct, date and analyse a species-level phylogeny of nearly all extant Mammalia to bring a new perspective to this question. Our analyses of how extant lineages accumulated through time show that net per-lineage diversification rates barely changed across the Cretaceous/Tertiary boundary. Instead, these rates spiked significantly with the origins of the currently recognized placental superorders and orders approximately 93 million years ago, before falling and remaining low until accelerating again throughout the Eocene and Oligocene epochs. Our results show that the phylogenetic ‘fuses’ leading to the explosion of extant placental orders are not only very much longer than suspected previously, but also challenge the hypothesis that the end-Cretaceous mass extinction event had a major, direct influence on the diversification of today’s mammals.

PanTHERIA: a species-level database of life history, ecology, and geography of extant and recently extinct mammals

Analyses of life-history, ecological, and geographic trait differences among species, their causes, correlates, and likely consequences are increasingly important for understanding and conserving biodiversity in the face of rapid global change. Assembling multispecies trait data from diverse literature sources into a single comprehensive data set requires detailed consideration of methods to reliably compile data for particular species, and to derive single estimates from multiple sources based on different techniques and definitions. Here we describe PanTHERIA, a species-level data set compiled for analysis of life history, ecology, and geography of all known extant and recently extinct mammals. PanTHERIA is derived from a database capable of holding multiple geo-referenced values for variables within a species containing 100 740 lines of biological data for extant and recently extinct mammalian species, collected over a period of three years by 20 individuals. PanTHERIA also includes spatial databases o...

The predictability of extinction: biological and external correlates of decline in mammals

Extinction risk varies among species, and comparative analyses can help clarify the causes of this variation. Here we present a phylogenetic comparative analysis of species-level extinction risk across nearly the whole of the class Mammalia. Our aims were to examine systematically the degree to which general predictors of extinction risk can be identified, and to investigate the relative importance of different types of predictors (life history, ecological, human impact and environmental) in determining extinction risk. A single global model explained 27.3% of variation in mammal extinction risk, but explanatory power was lower for region-specific models (median R2=0.248) and usually higher for taxon-specific models (median R2=0.383). Geographical range size, human population density and latitude were the most consistently significant predictors of extinction risk, but otherwise there was little evidence for general, prescriptive indicators of high extinction risk across mammals. Our results therefore support the view that comparative models of relatively narrow taxonomic scope are likely to be the most precise.

The fast-slow continuum in mammalian life history: an empirical reevaluation.

Many life‐history traits co‐vary across species, even when body size differences are controlled for. This phenomenon has led to the concept of a “fast‐slow continuum,” which has been influential in both empirical and theoretical studies of life‐history evolution. We present a comparative analysis of mammalian life histories showing that, for mammals at least, there is not a single fast‐slow continuum. Rather, both across and within mammalian clades, the speed of life varies along at least two largely independent axes when body size effects are removed. One axis reflects how species balance offspring size against offspring number, while the other describes the timing of reproductive bouts.

A species-level phylogenetic supertree of marsupials

Comparative studies require information on phylogenetic relationships, but complete species-level phylogenetic trees of large clades are difficult to produce. One solution is to combine algorithmically many small trees into a single, larger supertree. Here we present a virtually complete, species-level phylogeny of the marsupials (Mammalia: Metatheria), built by combining 158 phylogenetic estimates published since 1980, using matrix representation with parsimony. The supertree is well resolved overall (73.7%), although resolution varies across the tree, indicating variation both in the amount of phylogenetic information available for different taxa, and the degree of conflict among phylogenetic estimates. In particular, the supertree shows poor resolution within the American marsupial taxa, reflecting a relative lack of systematic effort compared to the Australasian taxa. There are also important differences in supertrees based on source phylogenies published before 1995 and those published more recently. The supertree can be viewed as a meta-analysis of marsupial phylogenetic studies, and should be useful as a framework for phylogenetically explicit comparative studies of marsupial evolution and ecology.

Garbage in, Garbage out

As in conventional phylogenetic analyses, issues surrounding the source data are paramount in the supertree construction, but have received insufficient attention. In supertree construction, however, the source data represent phylogenetic trees rather than primary character data. This presents several supertree-specific problems. In this paper, we examine several key data issues for supertree construction, including data set non-independence, taxonomy of terminal taxa, and the question of what constitutes a valid source tree. Throughout, we present our suggested protocol for source tree collection and manipulation based on our experiences in building a supertree of mammals. Other protocols and decisions are naturally possible. What is important is that all collection protocols are presented explicitly and address minimally the issues that we have identified.

TESTING FOR LATITUDINAL BIAS IN DIVERSIFICATION RATES: AN EXAMPLE USING NEW WORLD BIRDS

Study of the latitudinal diversity gradient to date has focused largely on pattern description, with relatively little work on the possible mechanisms underlying the pattern. One proximate mechanism is a latitudinal bias in the discrepancy between speciation and extinction rates, leading to higher rates of species diversification toward lower latitudes. Despite being central to many explanations for high tropical diversity, this mechanism is tested very rarely. We discuss some of the problems involved in testing for latitudinal bias in diversification rates and present an example phylogenetic analysis for endemic bird genera of the New World. The results provide evidence for higher diversification rates in clades inhabiting lower latitudes, both when genera are considered independent and when phy- logeny is controlled for using independent contrasts. High rates of diversification are also associated with larger geographic area and higher net primary productivity, although these do not fully account for the latitudinal effect. The latitudinal pattern is stronger in younger clades, supporting the prediction of a simple model in which the signal of latitudinal bias in diversification rates diminishes as clades age and become saturated with species. Our study demonstrates that a clade-based approach can help answer important questions that a geographic approach cannot, but large phylogenies and geographic databases are needed to cope with the large amount of noise inherent in this type of analysis.

Latitude and rates of diversification in birds and butterflies

Central to many explanations of latitudinal diversity gradients is the idea that rates of species diversification increase towards the equator. However, there have been few explicit tests of whether or not this pattern exists. Using sister–group analyses to compare 48 clades of passerine birds and swallowtail butterflies from different latitudes, I found evidence that relative rates of diversification per unit time are indeed higher towards the equator. This pattern is explicable in terms of abiotic factors which vary continuously with latitude, and may be further enhanced by diversity–dependent speciation and extinction processes.

Biological determinants of extinction risk: why are smaller species less vulnerable?

It is becoming increasingly clear that species of smaller body size tend to be less vulnerable to contemporary extinction threats than larger species, but few studies have examined the mechanisms underlying this pattern. In this paper, data for the Australian terrestrial mammal fauna are used to ask whether higher reproductive output or smaller home ranges can explain the reduced extinction risk of smaller species. Extinct and endangered species do indeed have smaller litters and larger home ranges for their body size than expected under a null model. In multiple regressions, however, only litter size is a significant predictor of extinction risk once body size and phylogeny are controlled for. Larger litters contribute to fast population growth, and are probably part of the reason that smaller species are less extinction-prone. The effect of litter size varies between the mesic coastal regions and the arid interior of Australia, indicating that the environment a species inhabits mediates the effect of biology on extinction risk. These results suggest that predicting extinction risk from biological traits is likely to be a complex task which must consider explicitly interactions between biology and environment.

Mistaking geography for biology: inferring processes from species distributions

Over the past few decades, there has been a rapid proliferation of statistical methods that infer evolutionary and ecological processes from data on species distributions. These methods have led to considerable new insights, but they often fail to account for the effects of historical biogeography on present-day species distributions. Because the geography of speciation can lead to patterns of spatial and temporal autocorrelation in the distributions of species within a clade, this can result in misleading inferences about the importance of deterministic processes in generating spatial patterns of biodiversity. In this opinion article, we discuss ways in which patterns of species distributions driven by historical biogeography are often interpreted as evidence of particular evolutionary or ecological processes. We focus on three areas that are especially prone to such misinterpretations: community phylogenetics, environmental niche modelling, and analyses of beta diversity (compositional turnover of biodiversity).