Precipitation and Flooding Decrease Salamander Metamorphosis Survival and Adult Abundance

Although several worldwide amphibian declines have been attributed to climate change, a lack of long-term data has limited studies of non pond-breeding species. In this study, Lowe (2012) analyzed the effects of climate change on Gyrinophilus porphyriticus, a stream salamander, in New Hampshire’s Merrill Brook from 1999–2010. Using capture-mark-capture surveys, Lowe compared observed salamander abundances to the results of annual abundance surveys in order to determine long-term trends for adults and larvae. He found that while larval abundances remained constant, the proportion of adults declined significantly. Their abundance was negatively related to annual precipitation, as increasing rainfall caused more flooding events. The trends observed can possibly be explained by the mortality of metamorphosing individuals increasing during spring and fall floods, leading overall to declines in adult salamander recruitment. If precipitation increases as predicted, the results of this study suggest that populations of stream salamanders may decline as a result of climate change.—Katie Huang
Lowe, W.H., 2012. Climate change is linked to long-term decline in a stream salamander. Biological Conservation 145, 48–53.
Lowe conducted his study by gathering samples along a 1-km long section of Merrill Brook, a stream in northern New Hampshire. Throughout 3-day periods in mid-June, mid-July, and mid-August of 1999–2004, he took capture-mark-capture surveys of G. porphyriticus by overturning 1200 rocks within the channel and capturing both larvae and adult salamanders with a dip-net. Individuals were marked by subcutaneous injection of fluorescent elastomer and data for length and life history stage were recorded. From 2005–2010, Lowe took annual abundance surveys by using the nearly the same methods as the capture-mark-recapture surveys except he ignored existing marks and did not make new ones. He then used count data from surveys in the Julys of 1999–2010 to test for trends in abundance as well as in the mean size of larvae and adults. He also tested if abundances were related to mean annual air temperature and cumulative annual precipitation using linear regression analyses. Finally, he modeled larval, adult, and metamorphosis survival probabilities to help explain long-term trends.
The results of the study found that adult abundance declined significantly from 1999–2010, although there was no trend in larval abundance. As larvae are likely to partially recruit independently due to the salamander’s long lifespan and multiple reproductive cycles, these results do not appear to be abnormal. However, it is possible that larval abundances may decrease rapidly once the adult population reaches a minimum threshold for larval recruitment. Adult abundances were also found to be negatively related to annual precipitation, which can possibly be explained by a decline in larvae surviving metamorphosis. Although larvae and adults had constant survival probabilities, metamorphosing individuals showed a downward survival trend from 2000–2003. Lowe suggests that since these individuals cannot exploit flood-avoidance strategies used by larvae and adults, flooding events caused by increased precipitation may increase susceptibility to mortality and reduce adult recruitment rates. In particular, this species of salamanders is exposed to prolonged flooding effects due to its extended period of metamorphosis. The author recommends further research between metamorphosis survival ability and declines in adult abundance. He also found that although there was no trend in larval size, the mean size of adults increased significantly. These results are consistent with reduced recruitment of smaller adults via metamorphosis and an aging adult population. If the adult abundance of G. porphyriticus continues to decline, the population may be led to local extinction, and similar results may be observed in other amphibians in other headwater systems in North America.

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