- - It's Frogtime!
||04-29-2010 01:50 PM
... in my garden pond. Actually, it's well past frogtime, but the frogs were about a month late showing up this year compared with the last few years following mild winters. You don't have to take my word for it, as this is also the conclusion of a large (>50,000 observations from across Britain) study just published:
Differences in spawning date between populations of common frog reveal local adaptation. PNAS USA April 19 2010, doi: 10.1073/pnas.091379210
Phenotypic differences between populations often correlate with climate variables, resulting from a combination of environment-induced plasticity and local adaptation. Species comprising populations that are genetically adapted to local climatic conditions should be more vulnerable to climate change than those comprising phenotypically plastic populations. Assessment of local adaptation generally requires logistically challenging experiments. Here, using a unique approach and a large dataset (>50,000 observations from across Britain), we compare the covariation in temperature and first spawning dates of the common frog (Rana temporaria) across space with that across time. We show that although all populations exhibit a plastic response to temperature, spawning earlier in warmer years, between-population differences in first spawning dates are dominated by local adaptation. Given climate change projections for Britain in 2050–2070, we project that for populations to remain as locally adapted as contemporary populations will require first spawning date to advance by ?21–39 days but that plasticity alone will only enable an advance of ?5–9 days. Populations may thus face a microevolutionary and gene flow challenge to advance first spawning date by a further ?16–30 days over the next 50 years.
The other thing worthy of note is the number of frogs. For the past few years, I've counted over 100 common frogs (Rana temporaria
) spawning in my pond at any one time. This year, following the hardest winter for over a decade, I was only able to count single figures. Which once again, is the exact topic of another research paper just published:
Decreased winter severity increases viability of a montane frog population. PNAS USA April 26 2010, doi: 10.1073/pnas.091294510
Many proximate causes of global amphibian declines have been well documented, but the role that climate change has played and will play in this crisis remains ambiguous for many species. Breeding phenology and disease outbreaks have been associated with warming temperatures, but, to date, few studies have evaluated effects of climate change on individual vital rates and subsequent population dynamics of amphibians. We evaluated relationships among local climate variables, annual survival and fecundity, and population growth rates from a 9-year demographic study of Columbia spotted frogs (Rana luteiventris) in the Bitterroot Mountains of Montana. We documented an increase in survival and breeding probability as severity of winter decreased. Therefore, a warming climate with less severe winters is likely to promote population viability in this montane frog population. More generally, amphibians and other ectotherms inhabiting alpine or boreal habitats at or near their thermal ecological limits may benefit from the milder winters provided by a warming climate as long as suitable habitats remain intact. A more thorough understanding of how climate change is expected to benefit or harm amphibian populations at different latitudes and elevations is essential for determining the best strategies to conserve viable populations and allow for gene flow and shifts in geographic range.
Climate change would be much less of a problem if it was a nice smooth progression rather than an erratic series of extreme weather events.
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