The symphony of nature

Though projections are complex and variable, changes in the climate are sure to impact the biological activity of organisms all throughout the world. Particularly, climate plays a major role in phenology, which are the various seasonal cycles of plants and animals within an ecosystem. Dr. Dustan refers to phenology as the symphony of nature, because blooming, breeding, and weather all coordinate beautifully to foster optimal conditions and community dynamics. However, as climate changes, the way that organisms respond varies, resulting in asynchrony – the ecosystem becomes less coordinated – which has implications for the community ecology.

For amphibians, phenology is particularly important, as frogs rely on temperature cues to start breeding so that they can obtain resources at their optimal yield, as well as coordinate with hydroperiods so to lay their eggs for development before drying occurs. To test the impact of temperature changes on frog breeding, Walpole et al. (2012) in “Community-level response to climate change: Shifts in anuran calling phenology” used temperature and calling data over 14 years (1995-2008) in Canada for seven anuran species, predicting that calls world correspond with warming temperatures. They also used climate change projections to consider these results for the future of anuran populations.

Calls were monitored at various temperatures throughout the spring and summer of each year (5, 10 and 15 degrees C) to get a range of species: Wood Frog (Lithobates sylvaticus),

Northern Leopard Frog (Lithobates pipiens), Spring Peeper (Pseudacris crucifer), Gray Tree Frog (Hyla versicolor), American Toad (Anaxyrus americanus), Green Frog (Lithobates clamitans), and the American Bullfrog (Lithobates catesbeianus). The authors also used climate projections under the Intergovernmental Panel on Climate Change (IPCC) 2007 report’s A2 emission scenario (conservative estimate) for 2070-2100.

The article found significant temperature increase for April during the 14 years of temperature monitoring, though not in May, June, or July. Of the frog call monitoring, the Wood frog, Northern Leopard frog, and Spring Peeper all called significantly earlier over the course of 14 years, and Gray tree frog and American toad had a trend of calling earlier, though not significant. These earlier calling times correlated with temperature for the Wood frog and American toad. Because the Wood frog, Northern Leopard frog, and Spring Peeper were all early-breeders, the authors considered these three species with regard to the IPCC scenario, which predicts a 4.06 degree C increase in temperature by 2070-2100. In this scenario, the authors calculate that calling time could be up to 11 days earlier for the Spring Peepers by these dates, and the Wood frog was predicted to be even earlier. For other species though, they were not projected to change calling time, which means that overall there will be a greater length of the anuran breeding season—starting earlier but ending just as late.

Specifically for the early breeding frogs (Wood, Northern Leopard, and Spring Peepers), pairing with temperature is necessary because they tend to utilize temporary ponds more than later breeding frogs. As such, this explains why they are more sensitive to temperature cues than later-breeding frogs do not use as temporary of pools. These findings about the impact of climate on phenology are important, as coordinated community ecology is critical for a stable environment, and changes to this coordination could be alter interspecific interactions. Generally, it may alter the dynamic of resource competition in species are no longer breeding all at the sam times, as well as predator-prey interactions.

In herpetology class we have discussed a number of ideas that allow us to understand what prompts frog breeding – and most of them depend on their environment and its phenology such as hydroperiods, temperature, and photoperiods. Because temperature is only one of the factors, a changing climate may do more than this paper proposes to offset frog breeding times. For example, if frogs are primarily triggered by temperature for breeding, then the water supply may be off and their ponds may not be full enough. If frogs respond more to photoperiods, then by the time they breed it may to too hot and dry for successful rearing. So though we have awareness of the types of phenological cues that frogs respond to, this paper shows that only some are correlated with temperature. As such, increased awareness about changing temperature, as well as determining how frogs respond to varying photo and hydroperiods is critical to understand the future of anuran populations in the face of climate change.

Walpole, A.A., Bowmani, J., Tozer, D.C., & Badzinski, D.S. (2012) Community-level response to climate change: Shifts in anuran calling phenology. Herpetological Conservation and Biology 7(2): 249–257.

http://herpconbio.org/Volume_7/Issue_2/Walpole_etal_2012.pdf