Synchronised Phenology and Climate Change - Part One: The Problem

The more avid blog followers amongst you will remember towards the start of this blog, when we discussed phenology. We discussed it with reference to our old friend the Pie Flycatcher (Ficedula hypoleuca), whom, according to studies by those such as Both and Visser (2001) and Goodenough etal. (2010), is falling behind the peak of food abundance due to diurnally triggered migration. Essentially, whilst the peak of prey species is creeping ever forward at home in response to increasing temperatures, the Pied Flycatcher is blissfully unaware and continuing to holiday in far flung regions, essentially getting left behind. In this and the next few blogs, I would like to take the opportunity to expand  upon this concept of phenology, exploring the important role it plays in keeping ecosystems functional, and offer a few examples as to how climate change, in a stunning turn of events, is throwing a spanner into the works.

I'm sure you remember our old friend the Ficedula hypoleuca

I would like to begin by briefly recapping on the concept of phenology, which was discussed so long ago and has been somewhat forgotten under the incessant waves of blogs exploring range changes and invasive species. Phenology, put simply, is the seasonal timing of certain events that occur in an organism’s yearly cycle.  According to Gienapp et al.(2014) phenology has incredible importance for the fitness of a species, as for most species there is a limited period wherein conditions are favourable for critical lifecycle events. Activities such as reproduction, hibernation and migration (as we have seen with the Ficedula hypoleuca) are essential for survival and proliferation, and can be at the mercy of how suitable a species phenology is to its surrounding ecosystem.

These ideal conditions can result from a variety of factors. Often they can be set by weather conditions, whereby a certain temperature or precipitation regime makes conditions favourable for specific activities. Other times, they can be dictated by the phenology of other species; this is typical in situations where predators are dependent on peak abundance of a certain prey species to enable energy-intensive activities such as breeding and rearing young (Gienapp et al 2014).

The essence of phenology

Generally however, the forces that influence phenology are climatic in nature. Due to year-to-year variation in the timing of certain climatic conditions, phenological characteristics that are directly or indirectly influenced consequently show a relative degree of plasticity – that is, are relatively flexible. However, the ability of ecosystems to adapt to short-term changes (those between years) is considerably greater than their ability to adapt to long-term changes, a phenomenon largely due to differential shifts across different trophic levels (Gienapp et al. 2014).

Species from different functional groups and trophic levels within ecosystems (essentially, those that perform certain functions or exist on different levels of the food chain) have experienced a varied magnitude of response to climate change, which over the years has caused significant advancements in phenology globally. These shifts, according to Gienapp et al. (2014), are typically more pronounced at lower trophic levels. Gienappet al. explain this variation as resulting from species reacting to differing environmental cues; for example, some species are sensitive to cues in separate periods (some species may be sensitive to winter peaks in temperature, whilst others to spring temperatures), whilst others are simply more sensitive to conditions such as temperature, with more of its functions influenced and hence will show greater plasticity. Some, like our unlucky friend the Pied Flycatcher, aren’t sensitive to climatic triggers at all, and instead rely on photoperiod (day length) triggers for phenology.

Phenology plays a critical role in all ecossytems - from the arctic to your back garden

Across the globe, this is causing huge problems for ecosystems. We are seeing increased instances of “decoupling” between phenological relations, which can cause mass disruption for trophic interactions through the altering of food-webs and can ultimately cause destabilisation of ecosystems. Studies such as those by Edwards and Richardson(2004), that investigates the effect of phenological shifts on pelagic ecosystems in the North Sea, and Visser and Holleman’s (2001) study on climatic effects on winter moth (Operophtera brumata) and Oak (Quercus robar) bud burst synchrony are two examples I will be discussing in the coming blogs that paint a very negative picture for the future of global ecosystems. We will also be exploring the range of effects that phenological change can have on inter-species interactions, such as what Stenseth  et al. (2015) investigate in their study on phenological effects on competitive relationships between Blue Tits (Cyanistes caeruleus) and Great Tits (Parus major).

Over the next couple of blogs, I hope that we can really develop an appreciation for the extent of what is really a very intricate and widespread problem. Phenological asynchrony, like range shifts and invasives, present huge barriers for ecosystems, and require an indepth and intricate understanding if we are to ever do anything to minimise the impacts of change on the life of our planet.