Azorean arthropods do it fast in dark caves

Azorean arthropods have diversified according to the age, area and relative isolation of each island within the archipelago. However, each group experiences these factors differently; hence their patterns of diversification differ according to their particular life histories. This is the main finding of a study conducted by Joaquín Hortal from the NERC Centre of Population Biology of the Imperial College, and Paulo Borges from the Azorean Biodiversity Group (CITA-A) of the University of the Azores, recently published in the Journal of Biogeography. The authors show that although the shape of the relationship between diversification and time is in general the same, different groups show different rhythms of evolution. They reach these conclusions within the first independent evaluation of the General Dynamic Model of Oceanic Island Biogeography, recently proposed by Robert J. Whittaker and colleagues, which merges the geological evolution of islands with the biological evolution happening on them. Borges and Hortal used the framework provided by this new model to study the relationship between the number of species that are single island endemics (i.e., exclusive of each island) and the age, area and isolation of each island.

'Caldeira' of Corvo, the smallest island of the Azores

Within the Azores, cave species appear to have evolved quite quickly, producing a number of species during the initial stages of development of the islands, when cave systems formed by lava tubes and volcanic pits were abundant and pristine due to the high volcanic activity. When the islands settle, cave systems start to collapse, diminishing the area available for cavernicolous species, which eventually end up either facing extinction or surviving in the small crevices of the soil under the forest. This rapid pace of diversification and early decline is exclusive to cave arthropods and does not appear to be evident for the other arthropod groups studied. In most islands some lineages are still evolving into new species, so older islands show more exclusive species than younger ones, except for the older island, Santa Maria, where some groups show some decrease in the pace of diversification. Such differences between groups are caused by the opposing roles of the two components of diversification. When speciation is predominant, diversification is positive and the number of endemic species on an island increases. This pace slows down as extinction takes the lead, and diversification gets slower and eventually negative when the islands age and erode and they start to lose species numbers. While for most arthropods the Azores is a land full of opportunities, those inhabiting caves already feel the pressure of living in aging islands.

Other factors, such as dispersal capacity, also affect the pace of diversification within the Azores, suggesting that the diversity of evolutionary responses in different kinds of organisms is so wide that no general model, like the one proposed by Whittaker and colleagues is able to predict the pattern and process of diversification of all living groups. What this model does, however, is to allow integration of deviations from the general pattern into a common theoretical framework. By relating these deviations with the particular characteristics of each group, we might be able to ascertain how and why evolutionary processes happen on the isolated archipelagos that constitute some of the few long-term experiments provided by nature.

Source paper: Borges, P. A. V. & Hortal, J. (2008) Time, area and isolation: factors driving the diversification of Azorean arthropods. Journal of Biogeography, doi: 10.1111/j.1365-2699.2008.01980.x.

Phylogeography of red deer in Europe revealed by mitochondrial DNA markers

Red deer (Cervus elaphus) is one of the most important and widespread game species throughout Europe, with an estimated population size exceeding half a million. The current distribution of red deer is assumed to be strongly influenced by human activities in addition to the colonization history and the last glaciation event. Due to the stationary habits of female social groups, the establishment of new populations by human translocations has often been reported. There are even historical data describing such translocations from the Viking sagas.
Worldwide, red deer has a circumboreal distribution, and genetic investigations have pointed to a central Asian origin. Despite its prominence as a big game animal, a detailed investigation of the genetic relationships of red deer populations in Europe has not been performed until now. As a consequence, the large (geographic) scale impacts of human translocations have not been known. In an article published in Journal of Biogeography, Anna Skog and co-workers report on the mitochondrial phylogeography of red deer in Europe.
Skog et al. analysed two regions within the mitochondrial genome from most European populations and by phylogenetic analyses of the gene sequences found that there are three main evolutionary lineages in Europe. The southern lineage is the most ancient. This genetic lineage is found in Africa in Sardinia/Corsica and at one site in Spain. The rest of Europe is populated by two genetically distinct red deer lineages, showing a western/northern and an eastern distribution, respectively.
Within each main lineage there are several variants, and the diversity and distribution of these variants give indications about putative glacial refugia. Skog and co-workers suggest that such refugia have existed in Spain (the Iberian Peninsula) and in the Balkans. Thus, the Western and Eastern clades have survived during the last glaciation in these regions and subsequently repopulated Europe from their respective refugia. This is further substantiated by calculations of how old the Western and Eastern clades are. Using the mutations separating the clades and estimated mutation rates for the genes, they calculated the split between the Western and Eastern clades to date at least 150,000 years ago, thus pre-dating the last glaciation.
Somewhat surprisingly, the analysis revealed no obvious signs of long-distance human translocations. While there is little doubt that this has happened in the past, the data of Skog et al. indicate that translocations have predominantly been short distance, or involved animals being translocated between regions where animals belong to the same main clade.

Source paper: Skog, A., Zachos, F.E., Rueness, E.K., Feulner, P.G.D., Mysterud, A., Langvatn, R., Lorenzini, R., Hmwe, S.S., Lehoczky, I., Hartl, G.B., Stenseth, N.C. & Jakobsen, K.S. (2008) Phylogeography of red deer (Cervus elaphus) in Europe. Journal of Biogeography, doi: 10.1111/j.1365-2699.2008.01986.x

Macroevolutionary mosaics – revealing the history for complex host–parasite systems

An emerging synthesis linking biogeography, ecology and coevolution provides a new framework to explore the structure and his-tory of intricate biological associations such as those represented by host and parasite systems. A general model, established by Dr. Eric Hoberg from the US National Parasite Collection, USDA and Dr. Daniel Brooks from the University of Toronto, for the evolution of parasite biotas emerges from empirical evidence describing a complex mosaic in which host switching and geographic colonization have served as determinants of diversity.
Complex assemblages of hosts and parasites are explained through coevolution and colonization and by integrating aspects of three hypotheses – ecological fitting, oscillation (episodes of increasing host range alternating with isolation on particular hosts) and taxon pulses (cyclical episodes of geographical expansion of ancestral species followed by isolation of populations producing descendant species, occasionally accompanied by ecological divergence, setting the stage for the next episode of expansion) – to establish a context for host and geographical distri-bution across varying temporal and spatial scales. Concepts are examined and framed by equating colonization with a breakdown in mechanisms for ecological isolation such as those driven by periodic global extinction, or episodic and cyclical climate fluctuation and environmental perturbation that have characterized marine and terrestrial systems in evolutionary and ecological time. Major radiations for assemblages of hosts and parasites, across nearly all taxa, have their roots in episodic events of extinction and biotic expansion in Earth history.
The synthesis signifies a conceptual shift from a mechanistically simplistic view of diversification through long-term mutual association and mutual modification of lineages to one involving an intricate historical mosaic involving host switches resulting from change in ecological context and geographic distribution. This view suggests that major episodes of climate change can trigger multiple rapid host switches, including those we call emerging diseases. This provides an appropriate ecological and evolutionary dimension for understanding patterns of introduction and dissemination of invasive species, and emergence of pathogens, parasites and disease in the current regime of global climate change with attendant disruption of ecological continuity.

Source paper: Hoberg, E.P. & Brooks, D.R. (2008) A macroevolutionary mosaic: episodic host-switching, geographical colonization and diversification in complex host–parasite systems. Journal of Biogeography, doi: 10.1111/j.1365-2699-2008-01951.x.

High-altitude small mammals of the North American Great Basin are not completely isolated

The term “sky islands” sounds intriguing, but it may be more lyrical than useful when discussing mammal distributions, according to new research from Eric Waltari of the Sackler Institute of Comparative Genomics at the American Museum of Natural History and Robert Guralnick from the University of Colorado at Boulder. The team used an emerging technique, ecological niche modeling, to show that the populations of small mammals living on mountaintops in the Great Basin—on islands in the sky—are not as isolated as previously thought.

Great Basin National Park (Nevada). Courtesy of the National Park Service.

In the new paper published in the Journal of Biogeography, Waltari and Guralnick test the concept of geographic isolation on thirteen species of small mammals. The species chosen were mapped with current and past climate data to “backcast” the distribution of each species at the height of the last ice age 21,000 years ago. The predictions of the model are calibrated with known fossil records. Backcasting allows researchers to test whether species had different distributions in the past; the current study, for example, found that most of the species (12 of 13) lived at lower elevations 21,000 years ago and that the average distribution of each species was larger than it is now.
Determining the area that species inhabited in the past helps researchers understand current population distribution within the Great Basin and potential linkages between “sky islands.” Many of the species in this study (9 of 13) had suitable habitat below their current range that could link different populations. This surprising result can be further tested with molecular research. Waltari and Guralnick also found that not all species were widespread across the basin 21,000 years ago, highlighting the idiosyncratic nature of species’ responses to climate change.
“Niche modeling is a quick and straightforward approach to addressing problems that molecular data will eventually solve,” says Waltari.

Source paper: Waltari, E. & Guralnick, R.P. (2008) Ecological niche modelling of montane mammals in the Great Basin, North America: examining past and present connectivity of species across basins and ranges. Journal of Biogeography, doi: 10.1111/j.1365-2699.2008.01959.x

Racing cane toads reveals they get cold feet on Southern Australia invasion

Source of article: Press release at Blackwell Ecology

Cane toads weren’t allowed to compete in the Olympics, but scientists have raced cane toads in the laboratory and calculated that they would not be able to invade Melbourne, Adelaide or Hobart and are unlikely to do well in Perth or Sydney, even with climate change.
According to research recently published in Ecography by Dr Michael Kearney, from the Department of Zoology at the University of Melbourne, and collaborators from Australia and the USA, the cane toad’s march will grind to a halt once it is physically too cold for the toads to hop.
“The cane toads cannot survive in much of Southern Australia because they would be too cold to move about and forage or spawn” said Dr Kearney.
Their study is unique in that it is based on an understanding of the capabilities of the toad itself whereas many other studies – some predicting that Melbourne would be invaded by the toads – are based on correlations between climate and the places the toads are living at now, which can lead to errors.
Since their introduction to Australia in the 1930s, cane toads have been steadily advancing across Australia and have already invaded Brisbane and Darwin. Once used as pest control, the toads are now a devastating pest themselves so an accurate prediction of their final range and rate of movement is essential.
If there were a cane toad Olympics, all eyes would be on the weather: because they are cold-blooded, the toad’s ability to move depends on its body temperature which fluctuates with its environment.
Dr Kearney and his colleagues, including Dr. Ben Phillips from the University of Sydney and Dr. Chris Tracy from Charles Darwin University, set up a 2m sprint event for toads at a range of different temperatures to see what temperatures would slow toads down the most.
The team used field-collected toads from four populations across the invasion front.
“We found that cane toads can barely hop once they get below about 15 degrees Celsius”, said Dr. Tracy. “Their range would also be constrained by the limited availability of water for their tadpoles in some parts of Australia”.
After racing their toads, Kearney and his colleagues used sophisticated computer models developed by Dr Warren Porter at the University of Wisconsin, Madison USA, to predict how cold toads would get at different times of the year across Australia.
They found that it is so warm and wet around Darwin that toads there can hop more than 50 kms per year. However, the cooler, drier conditions around Sydney or Perth mean that toads can barely manage 1 km per year. And they couldn’t move at all under typical weather conditions in Adelaide, Melbourne and Hobart.
They found that toads have particular difficulties in parts of southern Australia with what are known as Mediterranean climates – places with cold wet winters and warm dry summers.
“These are perfect conditions for growing wine, but you are unlikely to meet a toad at a winery” said Dr Kearney. In many of these places the air temperature at night – the active period for toads - is often above 15 degrees Celsius, but this only happens during summer, and evaporation in the dry summer air cools them down too much.
“Our study is particularly helpful in predicting where cane toads could live under climate change because we have identified a cause-and-effect way that climate limits the toads”. Dr. Kearney said.
“In one way it is obvious why dry conditions are bad for frogs – they lose too much water” explained Dr. Kearney. “But having wet skin also provides frogs with a thermal challenge because the evaporating water takes heat away from their bodies and often makes them colder than the air.”
They found that a moderate global warming could allow toads to move 100 km further south than their present limit by 2050. This would make conditions in Sydney slightly better for toads, and the only other city at risk of toad invasion under this scenario would be Perth.
Source paper: Kearney, M., Phillips, B.L., Tracy, C.R., Christian, K.A., Betts, G., & Porter, W.P. (2008) Modelling species distributions without using species distributions: the cane toad in Australia under current and future climates. Ecography, 31, 423-434.

Wind highways on the ocean drive the route and dynamics of migrations

In 2004, a group of Spanish researchers demonstrated, in an article highlighted as cover by Science, that invisible wind highways can explain why areas separated by thousands of kilometers can share a large number of species.
Now, two members of the original team, Ángel Felicísimo (Universidad de Extremadura) and Jesús Muñoz (Real Jardín Botánico, CSIC) have joined a birds' specialist, Jacob González-Solís (Universitat of Barcelona) to demonstrate that those wind highways follow a very precise route and, moreover, they are only accessible during very precise periods of time.
In the present paper, published in the open-access journal PLoS ONE, they used birds equipped with geolocators to identify the routes they follow in their migratory flyways, something in which González-Solís has been working for years. Cory's shearwaters (Calonectris diomedea), which breed in the Canary Islands and winter offshore South Africa and Namibia were the ideal candidates for two reasons. Firstly, because far from following the great circle route to cover the approximately 8000 km that separate the Canary Islands of South Africa, they follow a detour of 3000 km to almost reaching Brazil before turning east to Africa. How can it be profitable for a 800 g bird to make such immense detour? Secondly, they fly using a very peculiar technique: surfing the air that waves push in front of them. Given that ocean waves are produced by wind, nothing better than using the data generated by the satellite that measures wind's characteristics –the QuikSCAT, already used by Felicísimo and Muñoz in their previous research– to assess if shearwaters used the wind highways between Canary Islands and southern Africa.
Analyzing daily oceanic winds measured by QuikSCAT and comparing them with the birds' location, the authors found that the previously unexplained flyway followed by the Cory's shearwaters is exactly the most efficient during the migration time. Shorter pathways would represent higher energetic costs by flying against prevailing winds.

Minimum cost corridors according to SeaWinds in the migration period of Cory's shearwaters (left) and density of their trajectories (right).
Source: PLos ONE

Another result –this unexpected– is that the trip cannot be done in any time of the year, as there is an invisible temporal “gate” north and close to the Equator that is closed for months in the form of calms or contrary winds. Only when favorable winds start do Cory's shearwaters initiate their great joint southward journey.
In this research, the authors used new techniques specifically developed for these spatio-temporal analyses, which allow to mathematically demonstrate for the first time how winds constrain the main migratory flyways both spatially and temporally. These results open new avenues of research in fields like pathogens spread or when prophylactic treatments are more effective, species dispersal and migration, how species evolve after colonizing new areas, and even which species can be the ancestor of others.
Source paper: Felicísimo, Á.M., Muñoz, J., & González-Solis, J. (2008) Ocean surface winds drive dynamics of transoceanic aerial movements. PLoS ONE, 3, e2928.

The peninsula effect may yet be seen as a red herring, but more light is needed

The peninsula effect is a classic biogeographical concept which predicts that the number of species declines from a peninsula’s base to its tip. Two of three hypothesized causal mechanisms, the effects of geological history or habitat on species richness, can be controlled for by study design and/or statistical analysis. The third proposed mechanism (reduced colonization towards the peninsular tip) is attributed to peninsular geometry, and is less easily controlled. Dave Jenkins and Deb Rinne of the University of Central Florida asked two questions: (1) what is revealed by the 4-decade history of research on this concept; and (2) do microcrustaceans in Florida's isolated wetlands reveal a peninsula effect if the effects of history and habitat are controlled for?
Their literature review revealed mixed (49%) support for a peninsula effect, and found that most studies (86%) were not designed to control for alternative hypotheses or to quantitatively compare evidence regarding alternative hypotheses. Also, studies were strongly skewed to vertebrate animals (62% of studies); relatively little is known for other taxa. After controlling for history effects by study design, their own study of microcrustaceans in Florida wetlands revealed that habitat effects dominated (82.5%) the pattern, and virtually no effect of peninsular geometry existed. This result is consistent with effective dispersal of microcrustaceans through geological time.
This study is important because it shows that much illumination is still needed on the long-standing concept of a peninsula effect, and demonstrates that careful study design and statistical analyses can shed needed light. Peninsula effect studies should: broaden in taxonomic focus; control for alternative causative hypotheses (geometry, habitat, or history) in the study design; and quantitatively compare the effects of hypothesized mechanisms on peninsular diversity patterns.

Source paper: Jenkins, D.G. & Rinne, D. (2008) Red herring or low illumination? The peninsula effect revisited. Journal of Biogeography, doi: 10.1111/j.1365-2699-2008-01943.x.

Source of article: Journal of Biogeography highlighted papers

Uncovering genetic divergence and routes of gene exchange in the sand-obligate pallid kangaroo mouse, M. pallidus, from the Great Basin Desert

Kangaroo mice belong to the genus Microdipodops Merriam and are uncommon and rather bizarre-looking rodents, having enormous heads and large hind feet relative to their small (about 10 g) body size. The genus is endemic to the Great Basin of North America and includes two species: M. pallidus Merriam and M. megacephalus Merriam. The pallid kangaroo mouse, M. pallidus, is a sand-obligate desert rodent and this study examines its geographical distribution and formulates a phylogeographical hypothesis. This study also introduces a new analytical tool for testing orientation patterns in haplotype sharing for evidence of past episodes of gene flow.
The study examines mitochondrial DNA sequence data from early 100 individuals of M. pallidus sampled throughout its geographical range. The distribution of M. pallidus appears to be remarkably stable and is virtually unchanged from that determined three-quarters of a century ago. Unlike some other kinds of organism that show distributional adjustments in response to global climate change, there is no northward (or elevationally upward) distributional movement trend detected in M. pallidus.
Phylogenetic analyses show two principal clades, distributed as eastern and western units. The two clades are likely to represent morphologically cryptic species that diverged about 4 Ma. Results of this study (and a related study) now paint a picture of an endemic Great Basin taxon that diverged much earlier than thought previously and well before the creation of the extensive sandy environments during the Pleistocene and Holocene.
The directional analysis of phylogeographic patterns (DAPP analysis) used in this study is novel and may be useful in other studies. DAPP uses angular measurements of haplotype sharing between pairs of localities and circular statistical analyses to detect and quantify historical events pertaining to movement patterns and gene flow. DAPP analyses show significant, non-random angular patterns in both clades of M. pallidus. The phylogeographical patterns described here (both the eastern–western clades and the nonrandom directional patterns) may serve as a model for other sand-obligate members of the Great Basin Desert biota.

Source paper: Hafner, J. C., Upham, N. S., Reddington, E. & Torres, C. W. (2008) Phylogeography of the pallid kangaroo mouse, Microdipodops pallidus: a sand-obligate endemic of the Great Basin, western North America. Journal of Biogeography, doi: 10.1111/j.1365-2699.2008.01942.x.

Source of article: Journal of Biogeography highlighted papers

Global climate change is transforming Kakadu National Park

Kakadu National Park, Australia’s premier National Park, is being transformed by global climate change. Using advanced statistical analyses of historical sequences of aerial photography, Professor David Bowman, from the University of Tasmania, and his research team were able to show that woody plants have proliferated in the last 50 years within Kakadu’s savanna landscape and have transformed sections of treeless floodplains into tracts of scrub.
Such marked increase in woody cover is surprising given concerns about the impact of hostile fire regimes on the Park and the legacy-effects of an irruption of feral water buffalo that was finally brought under control by a sustained control programme in the 1980s. However, the analysis is consistent with a number of previous related studies undertaken by Bowman’s team. The cause of the expansion is related to a trend of increased rainfall in northern Australia and possibly the ‘fertilizer effect’ of increased atmospheric carbon dioxide, which favours growth of woody plants over that of tropical grasses.
The increase in woody vegetation has accelerated over the last 50 years because woody patch growth increases in a compound fashion. Such a non-linear pattern of woody increase has contributed to the erroneous belief that buffalo were the cause of the woody growth on the previously treeless floodplains – in fact the analysis showed that the buffalo control programme merely coincided with the dramatic expansion of woody plants.
The study is important as it shows the pervasive effects of global change on regional ecosystems. The expansion of woody plants is degrading wildlife habitat quality of Kakadu National Park’s iconic wetlands, particularly for water-birds that need treeless conditions. The upside, however, is that the park is capturing carbon in the woody growth. However, these effects may be transitory, as the IPCC’s recent climate change assessment has identified the Kakadu freshwater floodplains as being at risk of destruction due to sea level rise during this century.

Source paper: Bowman, D. M. J. S., Riley, J. E., Boggs, G. S. , Lehmann, C. E. R. & Prior, L. D. (2008) Do feral buffalo (Bubalus bubalis) explain the increase of woody cover in savannas of Kakadu National Park, Australia? Journal of Biogeography, doi: 10.1111/j.1365-2699.2008.01934.x.

Source of article: Journal of Biogeography highlighted papers

A new look at oceanic island biogeography

Oceanic islands have long fascinated biogeographers and ecologists, and indeed their study has played an important role in our understanding of the distribution and evolutionary origins of species. However, it is also acknowledged that the existing body of island biogeographical theory has been less successful and is less complete when applied to oceanic island systems operating on evolutionary timescales than where applied to less isolated archipelagos. This has led to repeated calls for the development of new theories of oceanic island biogeography, re-unifying ecological and evolutionary biogeography.
In a study recently published in the Journal of Biogeography, Robert Whittaker, Kostas Triantis and Richard Ladle present what they term a general dynamic model (GDM) of oceanic island biogeography. Their aim is to provide a general explanation of oceanic island biodiversity patterns through describing the relationships between fundamental biogeographical processes – speciation, immigration, extinction – through time and in relation to the island life-cycle. The argument is built on combining three premises: (1) that emergent properties of island biotas are a function of rates of immigration, speciation and extinction, (2) that evolutionary dynamics predominate in large, remote islands, and (3) that oceanic islands are relatively short-lived landmasses showing a characteristic humped trend in carrying capacity over their life span. Based on these premises, Whittaker and his colleagues derived several new predictions concerning the emergent properties of oceanic island biotas.
The authors go on to evaluate these expectations principally by means of simple analyses of proportions of endemics on each island within several oceanic archipelagos, finding broad support for the model, while noting that “The GDM is a deliberately simplified representation of diversity dynamics on oceanic islands”. As such it necessarily glosses over important details, but offers the promise of a more integrative and dynamic island biogeographical theory, and a framework for a renewed effort to integrate ecological and evolutionary approaches to the study of island biotas.

Source paper: Whittaker, R.J., Triantis, K.A. & Ladle, R.J. (2008) A general dynamic theory of oceanic island biogeography. Journal of Biogeography, 35, 977–994.

Source of article: Journal of Biogeography highlighted papers

Climate change and human hunting combine to drive the woolly mammoth extinct

Does the human species have mammoth blood on its hands? Scientists have long debated the relative importance of hunting by our ancestors and change in global climate in consigning the mammoth to the history books. A new paper, published in the open-access journal PLoS Biology, uses climate models and fossil distribution to establish that the woolly mammoth went extinct primarily because of loss of habitat due to changes in temperature, while human hunting acted as the final straw.
It has been particularly difficult to untangle these two potential causes of extinction, as climate change and increased human hunting are linked. When the climate in mammoth territory started to become too warm for the furry beast, it allowed humans—who couldn’t handle the lower, mammoth-friendly temperatures—to move into the area. Therefore, the mammoth faced the heat and predation pressure from hunting in the same regions at approximately the same times, making it difficult to test the importance of the two factors independently. It had also been argued that, as the mammoth had survived many temperature fluctuations previous to those that coincided with its demise, it was only human hunting that was a substantially different condition that could have caused the extinction of the species.
Work by David Nogués-Bravo and colleagues has ended the debate, by using mathematical modelling to separate the two factors. They used models of past climate to predict the potential distribution of the species at different times in mammoth history—126,000, 42,000, 30,000, 21,000, and 6,000 years ago—considering temperature and rainfall simulations alongside the age and locations of fossils. The results show that the mammoth suffered a catastrophic loss of adequate habitat, with the species 6,000 years ago relegated to 10% of the habitat available to it 42,000 years ago (when the glaciers were at their biggest).
In fact, things were much worse for the mammoth 126,000 years ago when globally high temperatures restricted its habitat even more than at 6,000 years ago. At both of these times, the climate-related habitat loss would have forced the species to the brink of extinction. The nail in the mammoth’s coffin 6,000 years ago was that, during the later extinction crisis, the mammoth also faced evolutionarily modern humans. Nogués-Bravo et al. estimate that, for an optimistic estimate of mammoth numbers 6000 years ago, humans would have had to kill only one mammoth each every three years to push the species to extinction. If they are pessimistic about mammoth-climate survival, that figure reaches one mammoth per human every 200 years.
Thus, it seems that, in the case of the mammoth, it was the climate that forced the species to the point of extinction, and it was mankind that gave the woolly beast the last shove into oblivion.

Source paper: Nogués-Bravo, D., Rodríguez, J., Hortal, J., Batra, P., & Araújo, M.B. (2008) Climate change, humans and the extinction of the woolly mammoth. PLoS Biology, 6, e79.

Carnivores in recent study help Bergmann's rule reach the 21st Century

Source of article: Blackwell's press release

In a new study in the journal Ecography, an inter­national team of researchers have analyzed Bergmann`s rule in European carnivore mammals.
Bergmann`s rule is one of the most studied and controversial “ecogeographical” patterns, and refers to the increasing body size of organisms towards higher latitudes.
Although it has been studied since the mid 19th Century, it is not until now that new statistical techniques have made it possible to disentangle the underlying influences of evolutionary history and ecology. In a new study in the journal Ecography, an inter­national team of researchers have analyzed Bergmann`s rule in European carnivore mammals. Their approach allows them to, for the first time, partition body mass variation into historical and ecological components. Doing this, they show that patterns can be better explained by recent and independent evolution of each species as a response to environmental conditions, and not only as a consequence of deep-time evolutionary events. Their finding provides a unified framework to interpret Bergmann`s rule across different taxonomic levels (within and between species) and solves controversies about its interpretation that have existed since the rule was first investigated in 1847.

Article:
Diniz-Filho, J. A. F., Bini, L. M., Rodríguez, M. A., Rangel, T. F. L. V. B. & Hawkins, B. A. (2007) Seeing the forest for the trees: partitioning ecological and phylogenetic components of Bergmann's rule in European Carnivora. Ecography, 30, 598-608.

DNA sequences and fossils show that Gonwanaland's Proteaceae spread by continental drift and transoceanic dispersal to modern continents

Source of article: Blackwell's press release

Using DNA sequence data, botanists have shown that the large southern hemisphere plant family Proteaceae lived on the super-continent Gondwanaland almost 120 million years ago. As Gondwanaland broke up, it was originally thought that these plants merely moved with the newly formed continents. But now a new study published in the Journal of Biogeography has shown that, while this is the case for some of these plants, others are far too recent to have lived at the time when the super-continent broke up. They must therefore have dispersed across oceans to reach their current distribution ranges.
Barker et al. apply a technique known as molecular dating to DNA sequences from over 40 representatives of the family from all southern continents. Using carefully selected fossils that are of known age and affinity, the mutation rate of the DNA sequences was calculated, allowing these scientists to provide age estimates for evolutionary events in the family. “Our results show that ancestors of some of the modern Proteaceae must have crossed the Atlantic and Indian Oceans. Thus, in Africa, for example, the spectacular genus Protea is truly Gondwanan, but 250 species from other genera that occur in the ‘fynbos’ vegetation (literally, ‘fine leaved shrubs’) of the highly diverse south-western Cape biodiversity hotspot are much younger, and have Australian relatives” says Nigel Barker of Rhodes University, South Africa.
This new finding is important, as it challenges the dogma that gondwanaland’s biota merely moved in situ with the continents as they broke up. “We have to reconsider the possibility of transoceanic dispersal, as unlikely as it sounds for these plants” says Peter Weston, a researcher at the Royal Botanic Gardens, Sydney, Australia. While this is not the first study to invoke dispersal, it is the first on a major and diverse Gondwanan plant family with complex distribution patterns. These results are not only relevant to botanists. Ornithologists will be intrigued to find that the age of the Embothriinae, a bird-pollinated group of Proteaceae in Australia, coincides with the estimated age of the Honey-eaters, Australian nectar-feeding birds.
Nigel Barker, the first author of the work enthuses “this study is the culmination of 11 years of work. I generated much of the data while working with Peter Weston at the Royal Botanic Gardens in Sydney in 1996. It was only when I met up with Frank Rutschmann in Zurich, who had the expertise on molecular dating, and Hervé Sauquet, a postdoc at the Royal Botanic Gardens, Kew, United Kingdom with an extensive knowledge of the fossil record of the Proteaceae, that it became possible to undertake this rigorous analysis. Sometimes science is about getting the right people with the right skills together in order to make advances”.

Article:
Barker, N. P., Weston, P. H., Rutschmann, F. & Sauquet, H. (2007) Molecular dating of the 'Gondwanan' plant family Proteaceae is only partially congruent with the timing of the break-up of Gondwana. Journal of Biogeography, 34, 2012-2027.

Fossil record supports evidence of impending mass extinction

The research team based at the University of York has, for the first time, discovered a close association between Earth climate and extinctions in a study that has examined the relationship over the past 520 million years — almost the entire fossil record available.

Matching data sets of marine and terrestrial diversity against temperature estimates, evidence shows that global biodiversity is relatively low during warm ‘greenhouse’ phases and extinctions relatively high, while the reverse is true in cooler ‘icehouse’ phases.

Moreover, future predicted temperatures are within the range of the warmest greenhouse phases that are associated with mass extinction events identified in the fossil record.

The research, published in the latest issue of Proceedings of the Royal Society B., was carried out by University of York student Gareth Jenkins, together with his supervisor, Dr Peter Mayhew, and University of Leeds Professor Tim Benton, both of whom are population ecologists.

Dr Mayhew says: "Our results provide the first clear evidence that global climate may explain substantial variation in the fossil record in a simple and consistent manner. If our results hold for current warming — the magnitude of which is comparable with the long-term fluctuations in Earth climate — they suggest that extinctions will increase."

Of the five mass extinction events, four — including the one that eliminated the dinosaurs 65 million years ago — are associated with greenhouse phases. The largest mass extinction event of all, the end-Permian, occurred during one of the warmest ever climatic phases and saw the estimated extinction of 95 per cent of animal and plant species.

"The long-term association has not been seen before, as previous studies have largely been confined to relatively short geological periods, limited geographical extents and few groups of organisms," says Professor Benton. "But the evidence is striking."


Article: Mayhew, P.J., Jenkins, G.B. & Benton, T.G. (2008) A long-term association between global temperature and biodiversity, origination and extinction in the fossil record. Proc. R. Soc. B 275, 47–53

Source of article: Univeristy of Your's Press Release

Are current projections of climate change-impacts on biodiversity misleading?

A recent study, published in Ecography, has profound implications for the future study of diversity on Earth. The article challenges the current view that patterns of current climate are sufficient to explain and predict diversity, and proposes that historical climate patterns are also of strong importance to diversity prediction.

This is the urgent question arising from the study “Quaternary climate changes explain diversity among reptiles and amphibians”, published in the journal Ecography.

Why is life on Earth not evenly distributed? Geographic patterns of species diversity and their underlying processes have intrigued scientists for centuries, and continue to spur scientific debate. Studies carried out over the past 20 years have led to the conclusion that species diversity is best predicted by contemporary patterns of energy and water, the so-called “contemporary climate” hypothesis. Because current climate gradients are correlated with past climate variability, it has also been suggested that current climate acts as a surrogate for evolutionary processes that have been triggered by past climate variability, giving rise to the “historic climate” hypothesis. Now, new high-resolution data on historic climate has allowed Dr Araújo in collaboration with Dr Rahbek and other colleagues to finally directly test the “historic climate” versus “contemporary climate” hypotheses of biological diversity. Their illuminating results are published in a recent paper in Ecography. Contrary to the expectations of many scientists they found that historic climate variability was a better predictor of reptilian and amphibian diversity in Europe than contemporary climate.

“The lack of quantitative spatial data on variation in climate over historical time has prevented more rigorous testing of these diverging hypotheses”, says Dr. Miguel B. Araújo from the National Museum of Natural Sciences (CSIC) in Madrid. As a consequence, “the debate on the causes of diversity gradients has turned to some degree into a discussion of semantics”.
Recent developments in general climate models have finally facilitated high resolution predictions of past climates. In collaboration with leading climatologists working on paleoclimate modeling in the United Kingdom, Drs. Araújo, Rahbek and colleagues provide the first comparative test capable of differentiating between the contribution of contemporary and historical climate drivers of diversity gradients across a complete lineage of species at a continental scale.

“In recent years, analytical attempts to shed light on the role of history in determining today’s patterns of species richness have focused on the strong residual variation of models using contemporary climate”, explains Dr. Carsten Rahbek from the Center of Macroecology at the University of Copenhagen. “It has been argued that these residuals provide information about the role of historical rather than contemporary constraints. However, such an analytical approach assumes that contemporary climate is the main explanatory force. In other words, the contemporary and historical hypotheses are not tested simultaneously in a directly comparable manner, and historical hypotheses are only invoked to explain what is left to elucidate after the implementation of contemporary environmental processes”, says Dr. Rahbek.

“Our results are striking in that they contradict previous studies of large-scale patterns of species richness” affirms Dr. Rahbek. “They provide the first evidence, using a quantitative analytical approach, that historic climate can contribute to current patterns of richness independently of, and at least as much as contemporary climate”. This study has profound implications for the study of diversity on Earth, and challenges the current view that patterns of contemporary climate are sufficient to explain and predict diversity.

Differentiating between contemporary and historical hypotheses is important, not only for theoretical reasons: “an understanding of the mechanisms that generate and maintain diversity provides valuable insights for predicting the impacts of contemporary climate changes on biodiversity”, says Dr. Araújo. “If contemporary climate does drive species richness, then current climate variables could be used to accurately predict the effects of climate change on biodiversity. If, as shown in our study, the mechanisms underlying contemporary patterns of species richness are in fact strongly influenced by the history of climate, then current-climate predictions may be seriously misleading and alternative approaches to predict the effects of climate change on biodiversity must be developed”.

Article:
Miguel B. Araújo, David Nogués-Bravo, José Alexandre F. Diniz-Filho, Alan M. Haywood, Paul J. Valdes, Carsten Rahbek Quaternary climate changes explain diversity among reptiles and amphibians Ecography. doi:10.1111/j.2007.0906-7590.05318.x

Source of article: Blackwell's press release

Editor's note: This is the first article of the new section of the IBS Newsletter and blog: "highlights in the literature". Highlights in the literature publishes press releases on exciting papers in all fields of biogeography. With this new section the IBS seeks to encourage popular writing of scientific papers in biogeography and help promoting biogeographical research outside the academic realm. If you have published, or are about to publish, a paper in biogeography and have prepared a press release in a widely accessible language, we are willing to consider its publication in the IBS Newsletter and Blog. Press releases of biogeographical paper must be sent to ibs@mncn.csic.es for consideration by members of the editorial board.