Amphibian population declines evolutionary considerations when dating

amphibian population declines evolutionary considerations when dating

amphibian populations, each with different man- the mechanisms underlying amphibian declines . important general consideration (Jung et al.,. ). .. ing inferring evolutionary potential of species. The majority of studies to date have. These empirical results show that amphibian species with restricted ranges should be threat risk correlates identified for almost all organisms examined to date. Additionally, because drivers of population decline are often . by the model under consideration, and the difference between the %DE for the. In the Declining Amphibian The Foreword Populations Task Force (DAPTF) .. worldwide and underlies most documented amphibian extinctions to date, .. local and regional demands, and projected evolution of resource use trends. and gaps that have to be taken into consideration for effective conservation of key .

Measuring the Meltdown: Drivers of Global Amphibian Extinction and Decline

It is important to realize that much evolution occurs through genetic changes that affect rates of development and mechanisms that control specific biological processes. Furthermore, evolutionary changes occur at different rates and on different timescales, depending on the organism.

For example, the evolutionary timescale may be in hours for bacteria, in weeks for certain fly species, and in decades for some vertebrate groups. A historical perspective Amphibians have evolved behaviors, morphologies, and lifestyles that have allowed them to persist for millions of years, since before dinosaurs existed on Earth and after dinosaurs' extinction.

But under today's environmental conditions, these same behaviors and life history characteristics appear to be placing amphibians in harm's way.

amphibian population declines evolutionary considerations when dating

To illustrate these points, we explore amphibians' responses to two basic problems that many animals confront every day: These two problems are especially significant because they appear to be contributing factors in the declines of a number of amphibian populations around the world Lannoo The examples and generalizations described below may apply differently in different regions of the world, and may vary between species and even between life stages and populations of the same species.

However, we believe our points about evolution are relevant to the phenomenon of amphibian population declines in general figure 1not only to the examples we provide.

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Amphibian evolution and exposure to sunlight Over evolutionary time, selection pressures have shaped the life history characteristics and behaviors of amphibians in ways that relate to their exposure to sunlight. Amphibians seek sunlight for thermoregulation and to maximize their growth and development.

Especially in temperate regions, larvae often seek shallow, warm water, which ultimately results in an increase in their growth rate Wollmuth et al. For example, Cascades frog Rana cascadae tadpoles are frequently observed in sunlit, warmer areas in the afternoon Wollmuth et al.

Mountain yellow-legged frog Rana muscosa tadpoles concentrate where water temperatures are highest near the shore during the day, deeper in the late afternoon and evening; Bradford In one study, all but the latest-stage bullfrog Rana catesbeiana tadpoles selected the warmest microhabitats Wollmuth and Crawshaw For example, Lillywhite found that more than 70 percent of the bullfrogs present in a pond were basking from 1: An observational study of R.

Juvenile western toads Bufo boreas often bask in the thousands along the shoreline Blaustein et al. Many amphibian species lay their eggs in shallow, open water in direct sunlight Behler and KingNussbaum et al. Eggs that are in shallow water, or even floating on the surface of the water, develop in a more oxygenated environment and probably in areas with a lower risk of predator or parasite attacks.

The oxygenation of eggs is critical to their development Duellman and Trueb In summary, amphibians living today often seek sunlight because, over evolutionary time, seeking sunlight has been beneficial for their thermoregulation, growth, and development, and perhaps for other reasons.

Amphibian Population Declines: Evolutionary Considerations | BioScience | Oxford Academic

Yet today's sunlight exposes amphibians to doses of UVB radiation that can kill or significantly damage them. Ultraviolet radiation in ancient and modern sunlight At the terrestrial surface, UVB radiation with a wavelength of to nanometers [nm] is extremely important biologically. Critical biomolecules absorb light with a higher wavelength UVA, to nm less efficiently, and stratospheric ozone absorbs most light that has a lower wavelength UVC, to nm.

UVB radiation can cause mutations and cell death.

amphibian population declines evolutionary considerations when dating

At the level of the individual, UVB radiation can slow growth rates, impair the immune system, and induce various types of sublethal damage Tevini Numerous organisms, including algae, crop plants, fishes, humans, and many invertebrates, can be harmed by exposure to UVB radiation van der Leun and BornmanBancroft et al. Animals have been exposed to sunlight and UVB radiation throughout their evolutionary history Cockell These traits may also be important in explaining population decline and extinction risk in frogs [8][11][12].

While we acknowledge that local drivers can be important, testing for major global drivers helps put local effects into a general context where they can be more easily evaluated, measured, and probably controlled. Our data represent nearly an order of magnitude more species than any previous study and have representatives from all three amphibian orders Anura [frogs and toads], Caudata [salamanders] and Gymnophiona [caecilians]something no other study has yet achieved see Table S1.

Measuring the Meltdown: Drivers of Global Amphibian Extinction and Decline

Our analyses are also based on the multi-model inferential paradigm that differs from Neyman-Pearson hypothesis testing in that the former achieves stronger inference in cases of multivariate causality [14] — [16].

This approach has been used successfully for exploring determinants of extinction and threat risk in other taxa [e. Additionally, because drivers of population decline are often decoupled from stochastic factors that cause eventual extinction [17]we determined whether declining amphibian species between and were affected by habitat loss, climate, life-history and ecology.

We examined the following specific, but related questions: For example, is there evidence for interactive effects between drivers on the risk of threat and population decline?

Spatial autocorrelation did modify model rankings and goodness-of-fit slightly Tables 1 and S6S7 and S8 ; even though the BIC evidence ratio indicated that the top-ranked model without spatial autocorrelation was nearly 14 times better supported than when it included spatial autocorrelation.

amphibian population declines evolutionary considerations when dating

In general, threat risk decreases linearly with an increase in the log of geographic range or body size. Other ecological and life history attributes received little relative support, with only weak evidence for life history habit terrestrial, aquatic, terrestrial-aquatic, or arboreal lifestyles and reproductive cycle terms.