J. Alan Pounds

Fingerprints of global warming on wild animals and plants

Over the past 100 years, the global average temperature has increased by approximately 0.6 °C and is projected to continue to rise at a rapid rate. Although species have responded to climatic changes throughout their evolutionary history, a primary concern for wild species and their ecosystems is this rapid rate of change. We gathered information on species and global warming from 143 studies for our meta-analyses. These analyses reveal a consistent temperature-related shift, or ‘fingerprint’, in species ranging from molluscs to mammals and from grasses to trees. Indeed, more than 80% of the species that show changes are shifting in the direction expected on the basis of known physiological constraints of species. Consequently, the balance of evidence from these studies strongly suggests that a significant impact of global warming is already discernible in animal and plant populations. The synergism of rapid temperature rise and other stresses, in particular habitat destruction, could easily disrupt the connectedness among species and lead to a reformulation of species communities, reflecting differential changes in species, and to numerous extirpations and possibly extinctions.

Widespread amphibian extinctions from epidemic disease driven by global warming

As the Earth warms, many species are likely to disappear, often because of changing disease dynamics. Here we show that a recent mass extinction associated with pathogen outbreaks is tied to global warming. Seventeen years ago, in the mountains of Costa Rica, the Monteverde harlequin frog (Atelopus sp.) vanished along with the golden toad (Bufo periglenes). An estimated 67% of the 110 or so species of Atelopus, which are endemic to the American tropics, have met the same fate, and a pathogenic chytrid fungus (Batrachochytrium dendrobatidis) is implicated. Analysing the timing of losses in relation to changes in sea surface and air temperatures, we conclude with ‘very high confidence’ (> 99%, following the Intergovernmental Panel on Climate Change, IPCC) that large-scale warming is a key factor in the disappearances. We propose that temperatures at many highland localities are shifting towards the growth optimum of Batrachochytrium, thus encouraging outbreaks. With climate change promoting infectious disease and eroding biodiversity, the urgency of reducing greenhouse-gas concentrations is now undeniable.

Biological response to climate change on a tropical mountain

Recent warming has caused changes in species distribution and abundance, but the extent of the effects is unclear. Here we investigate whether such changes in highland forests at Monteverde, Costa Rica, are related to the increase in air temperatures that followed a step-like warming of tropical oceans in 1976 (refs4, 5). Twenty of 50 species of anurans (frogs and toads) in a 30-km2 study area, including the locally endemic golden toad (Bufo periglenes), disappeared following synchronous population crashes in 1987 (refs 6–8). Our results indicate that these crashes probably belong to a constellation of demographic changes that have altered communities of birds, reptiles and amphibians in the area and are linked to recent warming. The changes are all associated with patterns of dry-season mist frequency, which is negatively correlated with sea surface temperatures in the equatorial Pacific and has declined dramatically since the mid-1970s. The biological and climatic patterns suggest that atmospheric warming has raised the average altitude at the base of the orographic cloud bank, as predicted by the lifting-cloud-base hypothesis,.

Climate and amphibian declines

Various reasons have been proposed for the falling numbers of amphibians in many parts of the world. Changing climate is likely to be a key factor — but with complicated links to the immediate causes of these population declines.

Ecology: Clouded futures

Global warming is altering the distribution and abundance of plant and animal species. Application of a basic law of ecology predicts that many will vanish if temperatures continue to rise.

Harlequin frogs along a tropical montane stream : aggregation and the risk of predation by frog-eating flies

We observed larvae of the fly Notochaeta bufonivora (Sarcophagidae) feeding on harlequin frogs, Atelopus varius (Bufonidae), along a gallery forest stream in montane Costa Rica during the dry season. Harlequin frogs tended to aggregate in areas containing waterfall spray, and in these areas an individuals probability of attack by Notochaeta was greater than in areas lacking waterfall spray zones. To ascertain whether this increased risk to a frog resulted from its choosing an area with a waterfall spray zone or from being in an area of high frog density, we manipulated the density of frogs in a series of quadrats. The results of this experiment suggest that the increased risk of attack in the environs of waterfalls was a hazard associated with patch choice by the frogs rather than with aggregation per se. AGGREGATIONS OF ANIMALS have often been viewed in the context of predator avoidance (e.g., Hamilton 1971, Bertram 1978). However, because predation events in nature are usually brief and unpredictable in space and time, one can rarely assess the relationship between an individuals risk of predation and its proximity to conspecifics. We studied an extraordinary predator-prey interaction between the harlequin frog, A. varius (Bufonidae), and a frogeating fly, N. bufonivoraz (Sarcophagidae), along a montane stream in Costa Rica. Harlequin frogs, which are brightly variegated with yellow and black, contain the potent nerve poison tetrodotoxin in their integument (Kim et al. 1975). Although tetrodotoxin probably discourages most predators, or at least most predaceous vertebrates, Notochaeta larvae, which feed internally, appear unaffected by this chemical defense (Crump & Pounds 1985). Because a frog lives several days after attack by Notochaeta, the probability of detecting predation events is much higher than is usually the case for predator-prey systems involving anuran prey. This paper focuses on the relationship between aggregation behavior of harlequin frogs and risk of predation by these frog-eating flies. Male frogs and toads commonly exhibit a clumped pattern of dispersion within the breeding habitat (Whitney & Krebs 1975, Wells 1977), and this pattern may reflect a patchy distribution of resources such as suitable oviposition sites. On the other hand, a clumped pattern of dispersion within the habitat may also be attributable to the advantages of aggregation itself. In theory, being in a group may dilute an individuals probability of being eaten should a predator arrive (Hamilton 1971); this may be especially important for aposematic prey, as a naive predator may avoid the rest of the group after sampling one individual. Also, if females are more attracted to groups of males than to solitary displaying males, the average mating success may be higher for males in groups (Wells

Global warming and amphibian losses; The proximate cause of frog declines? (Reply)

Alford et al. question the working model underlying our test for a link between global warming and amphibian disappearances, and Di Rosa et al. criticize our emphasis on a single proximate agent, the chytrid fungus Batrachochytrium dendrobatidis. Both teams report key pieces of the amphibian-decline puzzle and new evidence from different parts of the world that climate change is a factor in these losses. Here we show why our working model was appropriate and highlight the complexity of the imminent threat to species survival that results as global warming conspires with various other agents.

Amphibian mystery misread

A book blaming a fungus for the disappearance of amphibians from wild places wrongly downplays the role of environmental change, warn Alan Pounds and Karen Masters.