Synchronised Phenology and Climate Change – Part Three: A Range of Consequences

In my previous blog, “A Codding Mess”, we discussed one of the key implications that phenological change has for ecosystems. Specifically, we explored how such changes lead to desynchronization between trophic levels, ultimately reducing the efficiency by which energy is transferred up the food web and potentially destabilising ecosystems.

However, the effects of phenological change are not just limited to the relationships between organisms and their food sources; rather, these changes have a huge variety of effects on the relationships that exist between species and their biotic and abiotic environments, and it is these somewhat overlooked impacts which I would like to explore today.

To recap, the phenology of a species is the timing of an activity that has developed or evolved in order to synchronise life cycles with then seasonally changing availability of resources. Changing phenologies have been widely studied, although according to Lane et al. (2012), amongst other academics, this attention has focused mainly on the changing phenologies of avian species, as arguably these species are amongst those with the greatest sensitivity. An overlooked area of study, then, according to Lane et al.(2012), is that of the effect of phenological changes on hibernating species.

Hibernation is a survival response that is widespread amongst mammalian communities. Unlike their avian counterparts, who generally rely on migration in order to survive harsh winter conditions, hibernation has developed as what Lane ­etal. (2012) refer to as an “in situ” response for sedentary mammals to extended periods of low resource availability. The phenology of this hibernation, Lane et al. (2012) argue, can have profound implications for the consequent fitness of the animal in question, mainly through its influence over date of emergence. The researchers therefore highlight the effects of climate change on hibernators as a key area of study, in order to identify how these animals will be affected by changing climatic regimes.

The Columbian Ground Squirrel (Urocitellus columbianus)

In their study, Lane et al. (2012) attempt to begin a dialogue through their investigation into the effects of climate change on the phenology of Columbian Ground Squirrels (Urocitellus columbianus).  This species of squirrel have their habitat in the Rocky Mountains of North America, where the short growing season requires them to hibernate for around 8-9 months each year; the remaining time is split between mating (around 51 days) and then accumulating sufficient fat resources to survive until next year.

Delays in emergence then can have drastic effects on the fitness of these species. As they require 24 days for gestation and then a further 27 for lactation before fat reserves can be accumulated, any reduction in the time between hibernations can have serious consequences on their ability to accumulate sufficient reserves and hence survive the following period of hibernation (Lane et al. (2012).

Here, even though they have a relatively high degree of phenotypic plasticity, it seems that the situation is something of a “lose-lose” for the Columbian Ground Squirrel. During years of lower temperature and delayed snowmelt, which are becoming increasingly more frequent due to climate change, for phenology to remain the same would result in premature emergence, when snow cover still prevents access to sources of food for the species. However, the phenological plasticity of the species does it few favours either; by emerging later, the animals are effectively cutting short their active season. This is what is currently being observed by Lane et al. (2012), who note that hibernation emergence dates have been delayed by a period of 0.47 days a year over the past two decades, and this has resulted in consequent declines in mean fitness and population growth rates, a phenomenon that is set to only become more volatile over the next few years.

Another interesting study regarding the more unforeseen consequences of phenological change was published this year, authored by Stenseth et al.(2015). Through the analysis of four high-quality and long-term datasets, the group analyse the effects of climate change on the competitive relationship that exists between Blue Tits (Cyanistes caeruleus) and Great Tits (Parus Major) across Europe.

Climate change’s effects on competition can similarly have significant impacts for ecosystems. Competition, defined by Stenseth et al. (2015) as “the negative effects which one organism has upon another by consuming, or controlling access to, a resource that is limited in its availability”, plays a key role in ecosystem stability. Generally, within ecosystems, competitive relationships between species exist in a delicate balance that allows, to an extent, both to survive and reproduce without causing overt disruption to one another, whilst also preventing either species from becoming dominant (or creating a monoculture). This is the case in the majaority of ecosystems currently shared by Blue and Great Tits.

Here you can see the two engaged in something of a mexican stand-off

However, when you throw climate into the mix, as always seems to be the case, things get a little confused. This is exactly what Stenseth et al.(2015) found in one of their study locations. Through modelling how climate change will likely affect the parameters of competition models, they found that in Peerdsbos, Belgium, long-term climate changes would have a significant effect on the competitive interaction between the two species. Specifically, they noted that Great Tits generally would have greater abundance in cooler springs, and Blue Tits in warmer springs, and warned that these changes in population density may result in trophic cascades or even be the cause of future extinctions. Although Stenseth etal. (2015) cannot identify the specific mechanisms through which climate affects competition, the implications of this are serious enough to invoke further study.

By presenting you with these examples, I am trying to get across the point that the effects of climate change are incredibly pervasive and far-reaching. You can never take it at face-value, and the intricacies of its impacts are simply astounding. Some, when discussing phenological change, talk merely of desynchronization as the big issue, however as I have shown phenological change permeates every aspect of animals lives, affecting even their hibernation patterns and competition with other species. This point stands for all of the effects we have discussed, and throughout this entire blog I have tried to bring your attention to the otherwise overlooked impacts of climate change on our biota (such as this excellent blog on the effect of range shifts on genetics).

It is for this reason that extensive research into climate change and its effects on the biosphere are of critical importance. The effects it will have are so in depth and significant, that even with numerous dedicated teams of researchers we are still just scratching the surface. There is so much yet to learn, and if we ever hope to change the course climate change is taking for the natural world, let alone understand it, it is clear it needs to become a top priority.