Climate Change Ecology

contact persons: C. Both and C. Burger

 

Organisms are wonderfully adapted to the environments they live in, and natural selection provides a constant driving force to maintain this level of adaptation. Environments are, however, far from stable over long periods of time, and large changes in environments during short periods may be too rigorous to be tracked by successful adaptation. As a consequence, species may disappear locally, or even go extinct. If we want to understand human impacts on the functioning of ecosystems, it is crucial to study how well species are able to adapt to changes in their environments and whether these adaptations are sufficient to prevent population decline. The current rates of climate change are ideal for studying the process of adaptation because the change is predictable and big enough to occur in a researcher’s lifetime.

 

Climate change and breeding date

Our research has focused on how a long-distance migratory passerine has adapted to climate change. This birds breeds over a vast area across Europe and winters in West-Africa. In the Netherlands we have shown that during the last 25 years the breeding date of pied flycatchers has advanced by 8 days (Both & Visser 2001). In other populations across Europe the response was often different: in the north and east there was no change in breeding time, but in central and western Europe there was. The reason for these regional differences was variation in temperature change: in the areas without a change in temperature, breeding dates did not change. In contrast, areas with clear warming of spring, showed the strongest advance in breeding time (Both et al. 2004). This shows clearly that there is a response to local warming.

 

An insufficient response to climate change

Our next question was whether the advanced breeding date was the right response to the higher temperatures. This was not the case. Flycatchers rely on caterpillars for raising their brood, and caterpillars in temperate forests are only available during a short time window. Caterpillars can only grow well on young leaves, hence flycatchers must breed at that time, when food availability peaks. The caterpillar peak has advanced about twice as strong as the breeding time of the flycatchers, and hence flycatchers now breed too late (Both & Visser 2005). This was shown by a change in reproduction: nowadays only the very first breeding birds are capable of raising young that return as breeders in later years, whereas this was not the case in the past (Both & Visser 2001). Furthermore, pied flycatchers disappeared from areas with an early food peak, just because they were not able to advance their breeding in synchrony with the food (Both et al. 2006).

 

Migration as problem in adapting to climate change

Why did flycatchers not adjust their breeding time better to climate change? The reason may be their migratory behaviour. They winter in Africa and cannot see there whether spring is approaching in their breeding grounds. Therefore they have evolved a ‘decision’ based on day-lenght: birds that started migration at the right day to arrive just in time at the breeding grounds would have produced most young, and this beneficial behavioural rule therefore became most abundant. When spring advances at the breeding grounds, this rule becomes maladaptive, because birds migrate at the same time, and arrive too late at their breeding grounds. We could indeed show that arrival time has not changed strongly during the last decades, supporting the idea that migration is a problem in adapting to climate change (Both, Bijlsma & Visser 2005).

 

Future work

The main question of my current research is how long-distance migrants can adapt the timing of their annual cycle when the climate changes in order to maintain the synchrony with their environment. I will focus on the next issues:

1. Genetic variation in migration and breeding on which selection can act. We aim to measure whether parents that breed early also get offspring that breed early, and whether this resemblance is because of genetic resemblance. Because at present early breeding pairs produce more offspring, we can expect an evolutionary change if such a genetic variation exists.
2. Alternatively, the annual cycle of offspring may depend on environmental conditions. We have some evidence that early born young indeed migrate earlier in spring, probably not due to their genes, but because they were born early. I aim to test this by manipulating birth date, irrestively of genes, and measure subsequent arrival and breeding dates. This opens the possibility of ‘epigenetic’ effects: effects that are carried on to future generations without genetic differences involved. This may be the easy way to adapt to climate change.
3. Birds may move to other areas when the synchrony with the food peak in their natal environment is bad. Individuals that arrive too late in the Netherlands may thus continue migration to the north, until they reach an area with the right phenology (Coppack & Both 2002). This may not just benefit the individual bird, but may also speed up evolutionary change: new genotypes are introduced in this population, with earlier annual cycles, which opens new scope for selection.

References

Both,C., Artemyev,A.A., et al. (2004) Large-scale geographical variation confirms that climate change causes birds to lay earlier. Proceedings of the Royal Society of London , Series B , 271, 1657-1662.

Both,C., Bijlsma, R.G. & Visser , M.E. (2005) Climatic effects on spring migration and breeding in a long distance migrant. Journal of Avian Biology, 36, 368-373.

Both,C., Bouwhuis,S., Lessells, C.M. & Visser , M.E. (2006) Climate change and population declines in a long distance migratory bird. Nature, 441, 81-83.

Both, C. & Visser , M.E. (2001) Adjustment to climate change is constrained by arrival date in a long-distance migrant bird. Nature, 411, 296-298.

Both, C. & Visser , M.E. (2005) The effect of climate change on the correlation between avian life history traits. Global Change Biology, 11, 1606-1613.

Coppack,T. & Both,C. (2002) Predicting life-cycle adaptation of migratory birds to global climate change. Ardea, 90, 369-378.