The changing climate is impacting
organisms worldwide. Perhaps the most obvious change is in the timing of
events; Japanese cherries are blossoming earlier than they have for the last
1000 years, some migrating birds arrive at their summer grounds in the northern
hemisphere several weeks earlier than they did only 50 years ago, and others
lay two, not one, clutches of eggs per season. However, the directional trend
towards earlier phenology conceals substantial variation among populations,
species and higher. For example, great tit, Parsus major, and blue tit, Cyanistes
caeruleus, populations in Western Europe show considerable variation in
their phenological response to climate change, despite climate change itself
being relatively uniform across this geographic range. Tree swallows, Tachycineta
bicolour, in North America differ geographically in their response to local
climate change, with western and more southern populations exhibiting a
stronger response to climate change than eastern and northern populations.
Finally, the phenological response of both pied flycatchers, Ficedula
hypoleuca, and European starlings, Sturnus vulgaris, has been shown
to differ between the two species and between geographical locations. Despite
considerable evidence for differences in phenological response to global warming
between species and regions, the causes of this variation remain poorly
understood.
Although mostly
studied in birds and plants, the taxon that shows the strongest average shift
towards earlier breeding is amphibians. Amphibian populations have, on average,
advanced their breeding date at least twice as much compared to other animal
taxa for which comparable data exist. However, population changes in breeding
phenology in amphibians are also surprisingly variable. For example, only 2 out
of 7 studies of common toads report earlier breeding in more recent years, and
a recent study of 10 amphibians found significant shifts in only 40% of species.
The combination of large average responses and high heterogeneity among
populations and species calls for studies that attempt to address the causes of
this variation. This will enable better predictions for changes in breeding phenology
across different species and across different scenarios of global warming. Population
responses to novel environments in general, and global warming in particular,
should depend on the species biology (e.g. which environmental cues trigger
reproduction), the ecological conditions (e.g. to what extent.
Now, a new article in Ecography by Geoffrey M.
While and Tobias Uller (2014) conducted a phylogenetically controlled
meta-analysis of breeding phenology of frogs, toads and salamanders to examine
the extent of variation in amphibian breeding phenology in response to global
climate change. They show that there is strong geographic variation in response
to global climate change, with species at higher latitudes exhibiting a more
pronounced shift to earlier breeding than those at lower latitudes. The analyses
suggest that this latitude effect is a result of both the increased temperature
(but not precipitation) at higher latitudes as well as a greater responsiveness
by northern populations of amphibians to this change in temperature. The
authors suggest that these effects should reinforce any direct effect of
increasing warming at higher latitudes on breeding phenology. In contrast, they
found very little contribution from other location factors or species traits.
There was no evidence for a phylogenetic signal on advancing breeding phenology
or responsiveness to temperature, suggesting that the amphibians that have been
studied to date respond similarly to global warming.
Citation