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The geographic ranges of most plant and animal species are limited by climatic factors, including temperature, precipitation, soil moisture, humidity, and wind. These climatic variables determine the latitudinal and attitudinal limits for many species. A change in environmental conditions means that there is a strong likelihood that organisms will move from their present geographical range. So what does this mean for our plants fauna and flora under the pressure of today’s climate change? Are we going to witness mass movements of animals from one place to another? Or could we just loose our animal and plant species all together?
Firstly it is important to remind ourselves that this is not the first period in time that our planet has faced extreme climate change. Using fossil records and historical climate data, we can look into what effects previous climate change had on the planets fauna and flora. There may have been as many as 16 glacial cycles since the start of the Pleistocene (5 mya). Since the last glacial maximum 20 thousand years ago, global temperatures have risen by 8°C. So we should expect to see significant changes in the distribution of plants and animals since then.
Moreover, Norgues-bravo et al (2008) found that there was a dramatic decline in suitable climate conditions for the mammoth after the last ice age. Hospitable areas were restricted to Arctic Siberia, where the latest records of woolly mammoths in continental Asia have been found. The collapse of the climatically suitable area caused a significant drop in mammoth population size. This made them more vulnerable to increasing hunting pressure from expanding human populations. This last point is important to consider when we evaluate the risk to our current species, lost in a human dominated world.
Furthermore, the magnitude of temperature increases we’ve already experienced are likely to be dwarfed by those we’ll see in the next 100 years. In temperate regions, a 3°C change in mean annual temperature corresponds to a shift in isotherms of approximately 300-400 km latitude or 500 m in altitude. The changing climate is clearly going to effect not just our planets species but entire ecosystems as abiotic conditions change. Knowing roughly what changes we can expect to happen to the climate means we can also start to predict what might happen to our planets ecosystems.
Firstly, we can predict that some species might fail to keep pace with the climatic changes. Post-glacial temperature changes of considerable magnitude occurred over thousands of years. This allowed even the slowest species to migrate, and as Darwin noted, entire ecosystems to shift together. A 3.6°C increase in temperature over 100 years is unprecedented in geological history and many species simply won’t be able to keep up with the pace of change. Inevitably some species will get left behind and what effects will their loss have for ecosystem function? The stability and productivity of ecosystems is strongly influenced by species identify and number, so if species composition begins to change, so might ecosystem function.
Moving on, some species populations could tip over the edge of their range. Sooner or later even species that can disperse will run out of options. Mountains are of finite height, and continents of finite area. For example IPCC predictions show that the area of Tundra will decline by up to two thirds of its present cover by 2070 simply because it will have nowhere to move to. Mountain species can move their home further up the mountain to escape increasing summer heat waves, but eventually they will reach its peak. Whole ecosystems could be displaced, disrupting all biological processes involved.
Additionally, a similar problem with space is the effect it has on populations through a species-area effect. Land mass is not equally divided; mountain area declines with altitude and most continents tend to narrow as they approach the poles. Thus upward and pole-ward migrations mean species are crowded into smaller areas. Less area increases competition and adds pressure to the ecosystem. IPCC predictions show that despite moving further north, the area of Boreal forest will decline by 25% of its present cover by 2070. The decline is due this biome being squeezed into a smaller area than it currently occupies.
Still it must be noted that these changes will not happen on an individual level and it may take several generations for a species population to move to suitable conditions. For those animals that do not migrate, a distribution change in response to a warming trend would occur at the population level as a result of changes in the ratios of extinctions to colonization’s at the northern and southern boundaries of the range. A northward range shift would thus be reflected in either a net extinction at the southern boundary or a net colonization at the northern boundary. Range shifts in areas with regional warming trends have been reported in alpine plants, butterflies, birds, marine invertebrates, and mosquitoes. This process means that we must allow species protection from other threats in order for them to deal with a changing climate.
Moving on, the problem with climate change and the surrounding science is that a lot of it is based on predictions and it’s hard to quantify scientifically any current evidence. However, when it comes to species range shifts in response to climate change, we already have some concrete evidence that changes have begun. For example, Parmesan et al (1999) looked at ranges of non-migratory butterflies across North Africa and Western Europe over the C20th. Of 52 species examined, the northern boundaries were extended for 65%. Range shifts were 35 – 240 km northwards – broadly in line with the advance of the climatic isotherms over the same period.
This kind of biological reaction is not limited to individual cases. Hickling et al (2006) looked at the distribution of 16 terrestrial and freshwater taxonomic groups. 12 taxonomic groups (84% of species) showed northward shifts, including mammals, birds, fish and invertebrates. Thus there’s no apparent taxonomic, ecological or physiological pattern – lots of organisms are affected. One useful tool for conservationists trying to manage for these changes is the use of climate envelope modelling (CEM).
CEMs can be used in conjunction with ecological niche modelling to predict potential movements of populations. Assuming we know the niche characteristics of a species we can predict its distribution; past, present and future. Since climate is generally assumed to be essential to ecological niche space, temperature and rainfall are often used to predict distributions. CEMs describe the climate encompassing the current species distribution (or ecosystem) - this is then mapped to the location of this same envelope under a climate change scenario. Using these models can be important when planning conservation strategies for different species when considering a changing climate. Priority species and regions can be identified and money and effort can be directed where it’s most needed.
Still it can be hard for biologists to stress to the greater population just how important these changes are going to be not only for our planets ecosystems but for us. If habitats are changing and species are moving, we could start to witness unwanted species in important human areas. For example mosquitos with deadly tropical diseases have already been seen to extend their range and it will not be long before we have serious cases of malaria and yellow fever in Europe. Climate range shifts can also directly affect humans. The best example of this comes from Syria. The drought that played a role in triggering the catastrophic Syrian Civil war was the worst such climate event in the past 900 years. The climatic changes caused “mass migration” within the country from rural areas to urban centres, creating civil unrest. It’s not just animals and plants that depend on a certain climate, humans also depend on such variables and therefore we could continue to see major movements in human settlements.
Unfortunately, factors other than climate may limit the extent to which organisms can shift their ranges. Physical barriers such as mountain ranges or extensive human settlement may prevent some species from shifting to more suitable habitat. Conservation mangers must consider many factors when it comes to controlling natural populations under a changing climate. Conservation corridors must be put into place in order to allow the natural movement of species into new areas. However, even these measures could offer insufficient protection to populations. Instead, species persistence may require the radical action of managed relocation.
The fact is that our planet is experiencing unstoppable changes to the climate. Even if we did all we can to become “sustainable” we have already done so much damage that our climate is already set into a motion of change, we can limit this change but we still must prepare for what is already set to happen. Not just for the sake of our planets animal and plant species but also for the sake of human existence as we know it.
