Is it natural to change timing of natural events ?
Climate change is a ‘heated’ issue at the moment and we all now know that average temperatures have already risen roughly by 1° and are predicted to rise more by up to 6° by the end of this century. The already apparent changes in our ecosystems are geographical range shifts, phenology of organisms, ecosystem functioning and composition.
Latitudinal and altitudinal limits of many species are dictated by climate. Thanks to pre- and post-glacial projections, we know that in the past whole biomes had shifted – New York used to be tundra but now is covered in temperate deciduous forest, and tundra moved further north. With current temperature rise, changes like these might not stay only a legacy of the past…
But what exactly causes geographical shifts in distribution?
Each species has a potential niche, or a location, in which it can survive under certain climatic conditions and it is physiologically impossible for it to survive outside this niche – this is known as its ‘climate envelope‘. A change in a condition i.e temperature will affect the growth and survival of an organism, so it shifts its distribution to stay within its climate envelope. This can be nicely seen in a recent example of shrubs expanding into tundra of Alaska, Russia and Canada due to warming air temperature. It was shown that species spread an order of magnitude faster in marine than in terrestrial ecosystems – in Atlantic Ocean, some copepods shifted their range by 1000km polewards in recent years!
Increase in temperature might mean that some species can expand their present range. Although this might sound positive at first, it is especially true for invasive species as these generally have a broader range of tolerances (= a bigger climate envelope). An example of an economic importance is that of the mountain pine beetle, which introduces tree-devastating blue stain fungus. The outbreaks in the population are usually controlled by cold winters but as temperatures have risen the beetle has been able to expand its range into previously unsuitable climate areas. The recent outbreak in western-north America is the largest recorded in history, impacting over 14million ha of pine forests. Range expansions were observed in other invasive species such as zebra mussel, and Chinese mitten crab.
Growth and reproduction, the two main activities that drive life on this planet, are in other words chemical reactions and so are temperature-dependant. Because temperature is seldom limiting in the tropics, we expect to see the biggest effects in temperature-limited temperate species. It is not only the rate of these reactions that is affected, but also their timing – or phenology (= the timing of natural events such as emergence, breeding, migration, snow cover).
In plants, bud emergence has generally advanced, with spring starting ever earlier in the Northern Hemisphere. On the other hand, in countries with long winters such as Poland, growing season starts later.
Both of these changes can have immense impact on other species. In Colorado, Yellow-bellied marmots emerged from their hibernation 38 days earlier over a 23-year period in response to warmer springs. Elevated temperatures cause increase in spring precipitation, however in high altitudes increased rainfall = not more rain but more snow! 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 porcupines, 95% of their death is by predation and so longer periods of snow cover (where they are not camouflaged) might negatively impact on their populations.
Many organisms bring forward the timing of their seasonal activities, whether it be flowering in plants, or emergence of insects. Some species, however, may not cope with climate change because their response differs from the response of organisms at lower levels of the food chain –> predator-prey mismatch. In the Netherlands, caterpillars, which are the main food source for juvenile pied-flycatchers started emerging earlier but the birds failed to advance their breeding timing and so breed after the time of maximal food abundance à as a result there is not enough food for them when they have hatchlings and so populations declined by 90% in last two decades!
The high Arctic has the world’s simplest terrestrial vertebrate predator–prey community, with the collared lemming being the single main prey of four predators, the snowy owl, the Arctic fox, the long-tailed skua, and the stoat. If lemming population was to be affected by earlier snow melt, all of its predators might be in trouble! Similarly, in marine ecosystems, trophic cascades can be triggered if either the main prey or predator species is removed by climate change.
Although it is sometimes possible to predict reactions of organisms to climate change, every species responds slightly differently and so there
is bound to be a big asynchrony. This makes conservation planning exceedingly challenging. Even the most obvious cases such as decreasing polar bear populations and ocean acidification still does not have conservation answers. How are we going to tackle things such as loosing keystone species = loosing ecosystem (such as Dave’s myccorhizal example) or temperature-dependent sex determination species. Janzen predicted that a 4° increase in temperature will practically eliminate males from painted turtle population. Perhaps species like these should be the main concern of current conservation efforts and not big fluffy pandas, who are not in an immediate threat of extinction and nevertheless millions are being spent on their conservation.