Late for a Very Important Date


Our climate is drastically changing at a rate never before seen on earth. Though the majority of the general population are aware of some of the major effects of this phenomenon such as the melting of our ice sheets and death of our coral reefs, there are many aspects of climate change that receive very little attention even in the research aspect. One troubling aspect of climate change is how the patterns in an animal’s life will be effected by the changing climate and how that may affect relationships between species.


An individual’s life history comprises progressive stages in its development, maturation, reproduction and eventual mortality. A suite of traits is associated with this progression. Traits typically of interest in a life history are the timing of emergence, hatching, or birth; size or length at emergence, hatching, or birth; timing of the annual period of reproduction; age or size at which the onset of reproduction occurs; age or size at which reproduction ceases; and age or size at the time of death. The study of the timing of life history events and the manner in which they vary in space and time constitutes phenology. It is becoming evident that climate change could cause major issues with species phenology’s.


Elevated temperatures, increased rainfall and changes to growing season will affect both the timing of natural events and where they happen. Based on a close association with temperature, plant phenology is expected to be one of the most responsive and easily studied traits in relation to climate change. A clear trend for earlier spring phenology has already been reported in the literature. Root et al (2003) used 10 years’ worth of data to study the spring phenology of 694 plant species. The mean number of days of advancement in phenological traits was 5.5 days per decade. Advanced leaf emergence has been witnessed across the Northern Hemisphere, the acceleration in CO2 emissions during the latter part of the C20th has been link to this advancement.


When it comes to animals there are three main aspects of their life histories that could be easily affected. The emergence from hibernation, the timing of migration events and perhaps most importantly the timing of breeding events. If these aspects of an animal’s life are altered by the changing climate it could seriously affect the survival and fitness of not only individuals but also the health of species populations.


Firstly, emergence refers to the end of hibernation. This is usually triggered by spring temperature rises. As previously mentioned the oncoming of spring is advancing, meaning that many hibernating animals are emerging sooner than usual. One study compares the time of first sighting yellow-bellied marmots (Marmota flaviventris) with temperatures in the Colorado Mountains. Over a 23 year period marmots emerged 38 days earlier in response to warmer springs. There’s a potential problem for marmots though since elevated temperatures increase spring precipitation, and snow melt has slowed with increased air temperature. Thus the interval between the end of hibernation and the beginning of the plant growing season has lengthened and increased the cost of maintaining a high body temperature in the absence of their food plants.


Another study in Wales looked at spring emergence in smooth (Triturus vulgaris) and palmate newts (T.helveticus) found a more positive outlook. There was a significant advance in emergence time for both species of 2-5 days per year. However, Palmate newts emerged earlier in warmer years, this differential response between the two species could reduce competition for breeding sites etc allowing both species to perform better. These two examples show how we cannot predict the effect of changing climates on emergence as different species have different reactions.


Furthermore, the advancement of spring is likely to effect the migration patterns of many species. There are many species who spend the colder winter months in more productive environments and then move back to their home ranges when the conditions improve. A good example of how migration timings are changing comes from Robins who over-winter at lower altitudes before moving back to the mountains to breed in the spring. Robins were arriving earlier, a shift about 9 days over 26 years. Unfortunately they face similar problems to the marmots – delayed snow cover, seriously affecting survival of the species.


Perhaps the trait which could be most drastically effected is that of breeding. Probably the longest and largest data set on breeding phenology derives from the BTO’s nest recording scheme. This was started in 1939 and collects breeding information for about 120 species of British Birds. Initial analysis of data for 65 species over a 25 year period (1971 – 1995) showed that 20 laid eggs significantly earlier and 51 species showed a trend towards earlier breeding.


Clearly the changing climate is already effecting the lives of many species. However, these shifts in pehenolgies pose major problems for the interactions between different species. Whether its pollinators and their plants or predators and prey, different species are reacting to the changing climate in different ways and this could seriously disrupt the relationships between species. Predators often synchronise reproduction with high prey abundance however shifts in prey phenology may not be tracked by predators creating a mismatch. Mismatch is likely when predators and prey rely on different abiotic cues for example typically predators rely on annually fixed cues (day length) whereas prey species rely on cues which vary year to year (temperature).


This mismatch can have knock-on effects throughout an entire food chain. One of the best studied relationships is that between Great tit reproduction and caterpillar abundance in The Netherlands where the timing of egg-laying in Great Tits has become increasingly out of Synch with peak abundance of the major food source for chicks. While caterpillar emergence has advanced with warmer springs, great tit reproduction has failed to keep track with these changes. The result is that chicks are no longer hatching to coincide with the peak in caterpillar abundance.


One of the Great Tits main predators, the sparrow hawk, also seems to be having problems keeping up with shifting prey phenology. Comparison of breeding phenology of sparrow hawks with that of 5 passerine species representing 35% of its prey species shows all 5 species having advanced egg laying and fledgling of their young, but sparrow hawks showed no evidence of advanced breeding phenology, despite the fact that their chicks depend on newly fledged prey. This means an increasing lag in sparrow hawk chick emergence behind fledgling of prey - newly fledged passerines are easy to catch, so any delay in chick emergence means prey are harder for adults and newly fledged sparrow hawk juveniles to catch. This example shows how a small change in climate can have knock on effects that can drastically alter not just a species survival but also an entire eco-systems.


These mismatching events could also come back to affect us humans. For example if pollinators are changing their patterns of emergence etc our crop seasons could change or even fail. Our fish industry is already been effected for example jellyfish are emerging much earlier in spring but populations of copepod prey have not yet shifted to spring warming. And so the copepod populations are vastly decreasing. This is an issue because other predators such as fish larvae will have increased competition and the jellyfish will start to predate on fish eggs.


It is clear from all the studies discussed here and many more that the changing climate is effecting the phenologies of our planets species. Individual species may be able to find ways to cope with such changes but species in the wild are not in isolation. The worrying thing is how these changes will affect the ecosystem, if some species are changing one way and others differently. It is important for us to continue to monitor the adaptability of every ecosystem in order to help protect them. The real answer to halt these problems is to try and halt any further climate change, we must adjust our lives and become more environmentally conscience if we want to keep our planet in equilibrium. Not only for the worlds many species to continue to flourish but also so we can continue our existence.


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