Global climate change is predicted to cause temperatures to increase by 1.4-5.8ËšC by the year 2100. This will likely have a profound impact upon many land animals. Here, four animal groups were selected for review; amphibians, insects, polar bears and birds. Many species will most probably move further north, where conditions will be cooler. Changes in breeding will occur, with many species breeding earlier, as already demonstrated by amphibian and bird species. Higher temperatures are likely to benefit insects, causing higher metabolic rates and increasing their numbers. Alternatively, a warmer future for polar bears doesn’t look promising. With rapid loss of sea-ice, many individuals are suffering, as obtaining food is becoming increasingly difficult. Predicting the likely impacts of climate change is complex as each species will be affected differently. Further research is needed to predict the impacts of rainfall patterns and extreme weather events upon the survival of land animals.
Abstract 2
Global climate change is well under way, with global mean annual temperatures set to increase by 1.4-5.8ËšC by the year 2100. This major environmental change has the ability to influence both species distribution and extinction rates. Here, four animal taxa were selected for review; amphibians, insects, polar bears (Ursus maritimus) and birds. Northern distribution shifts are likely to become increasingly common across all groups as species exploit new habitats and seek cooler conditions. Phenological changes will take place such as earlier breeding in amphibians and birds, though it is uncertain about what this will mean for their persistence. Climate-facilitated diseases may influence extinctions, such as Saprolegnia ferax, which causes mortality in amphibian embryos. Higher temperatures are likely to benefit insects, causing an increase in flight-dependent activities. Alternatively, a warmer future for polar bears doesn’t look promising. With rapid loss of sea-ice, the body conditions of many individuals are declining, and desperate foraging strategies such as cannibalism have been reported. Predicting climate induced effects is complex as responses will be specie-specific and potential evolutionary adaptations need to be taken into account. Further research is needed to predict the impacts of precipitation and extreme weather events upon the fitness of terrestrial species.
1.0 Introduction
Long term global climate change is currently at the forefront of scientific interest. Climatic variation is undoubtedly a natural process, but the balance of evidence available suggests that excessive human activity has been the dominant reason for the recently observed dramatic changes in climate (Telemeco et al, 2009). Records have shown that since the 1970s, global mean annual temperatures have increased significantly, rising by approximately 0.15ËšC per decade (Beaumont and Hughes, 2002). It has been predicted that this trend will continue, and global mean annual temperatures are likely to have increased by 1.4-5.8 ËšC by the year 2100 (op.cit). Some researchers believe that such temperature rises will be “the largest anthropogenic disturbance ever placed upon natural ecosystems” (Deutsch et al, 2008). Whilst this warming has received a great deal of attention, changes in precipitation patterns and the frequency of extreme weather events will accompany this temperature variation. These recently devised predictions are causing immense concern amongst scientists, because assuming that they are correct, the biodiversity across the globe will be altered significantly. Distribution, the geographical occurrence or range of an organism, is mostly controlled by climate, and therefore, it is anticipated that this will be notably affected in numerous species (Pearson and Dawson, 2003). Studies have shown that global climate change has already taken effect and has been the cause of numerous distribution shifts observed in a variety of organisms during the past 30 years (Thomas et al, 2004). A study carried out by Hitch and Leberg (2006) found that distributions of North American bird species were moving significantly further north, most probably as a result of increasing temperatures. The extent to which animals react to global climate change, whether it be through changing their distribution or reacting in others ways, will depend largely upon several factors. The first is the geographical location of the species and the second being the presence of particular biological traits. These traits are related to factors such as genetic make-up, ecology and life history stages, influencing an individual’s vulnerability to climate change. Specific traits include dependence upon a particular microhabitat, dispersal limitation due to geographical barriers and low genetic diversity (Foden et al, 2008).Therefore, not all species will respond in similar ways, even when exposed to the same climatic conditions, meaning that the persistence of some species will be threatened more than others. Extinction, due to climate change, will be the likely reality for some species, and it has been estimated that 15-37% of terrestrial species will be ‘committed’ to extinction by the year 2050 (Thomas et al, 2004). Research is currently very much centred on trying to identify those most at risk and looking for possible ways to reduce predicted extinction rates. Though much effort is being made, minimizing the emission of greenhouse gases, primarily carbon dioxide, is the single ultimate action which could save a vast number of species (op.cit). The publication of a growing number of studies regarding extinction in relation to climate change is making humans increasingly aware of the vital actions that need to be taken in an attempt to conserve the earth’s biodiversity.
1.1 Aims
The aim of this review is to evaluate how global climate change will affect the distribution and status of both terrestrial vertebrate and invertebrate species. ‘Status’ is quite a broad term but in context of biology and hence this review, it primarily refers to ‘conservation status’; examining how likely the animal is to become extinct in the future. Predicting the status of an organism is complicated and requires information regarding various aspects of its ecology, such as its habitat, foraging strategy and breeding behaviour. Research concerning a variety of animal groups will be examined, so that a wide range of potential effects across the animal kingdom can be identified. Here, four taxonomic groupings have been selected for review, due to their high vulnerability to climate change and/or high environmental importance. These taxa are also heavily represented in the available literature. The polar bear (Ursus maritimus) has been focused on due to its rapidly changing ice habitat. Insects and amphibians were selected mainly due to their ectothermic nature and are therefore highly sensitive to temperature. Finally birds were chosen due to their close association with climate, especially in migratory species. Although not every animal class has been reviewed, it is hoped that this literature review can provide a balanced evaluation with regards to an area of science which is causing both increased social interest and concern at the present time.
2.0 Amphibians
It is widely accepted that amphibian populations are declining dramatically around the globe, with an estimated 43% of the total species currently in decline (Lips et al, 2008). This has prompted a satisfactory number of studies, which have researched the possible factors responsible for amphibian reductions (Corn, 2005). Though climate change as a cause was considered relatively understudied in 2003, it has since received an increasing amount of attention (Carey and Alexander, 2003). Amphibians are terrestrial ectotherms, having life history stages which are very much sensitive to both environmental temperature and precipitation (op.cit). This suggests that they should be highly vulnerable to climate change, but past records have shown that existing amphibians have descended from ancestors that were able to cope with climatic extremes and variability (op.cit). Nevertheless, it still remains highly important to discover if, and how these animals will be affected by global climate change in the future. Understanding links between amphibian distribution and climate change is essential for their conservation, though relatively few studies have investigated this. Girardello et al (2010) undertook a study in an attempt to discover the likely implications of climate change on the distribution of amphibians in Italy. It was confirmed that climate greatly affects species distribution and precipitation plays a crucial role in determining range shifts (op.cit). Negative predictions were made in that the distributions of many amphibian species could reduce considerably. Mediterranean species such as Rana temporaria and those found in mountain habitats are of a main concern, as it was found that their distributions could decrease, despite the fact they may well colonize new areas (op.cit). One of the reasons for this is that many species in these particular locations are highly climate specialised (op.cit). Therefore, any small changes in climate could prove to be damaging in terms of their distributions. Distribution reductions are not only predicted for species in Italy but for those in other countries too. It is expected that the golden striped salamander (Chioglossa lusitanica), native to Spain and Portugal, will constrict its distribution between the years 2050 and 2080 (Corn, 2005). Research regarding 42 amphibian species throughout Europe produced somewhat more promising conclusions. It was found that temperature predictions for 2050 are not likely to be a major threat to this group of animals, and it was also concluded that they can be expected to expand their distribution (ArauÌjo et al, 2006). This is due to the fact that the warming of northern European areas will create new habitats, which species can exploit (op.cit). However, this will only be possible if the ability to disperse is unlimited. (Figure 1 illustrates the predicted species extinctions with no dispersal/unlimited dispersal in Italy). The involvements of factors which prevent or reduce dispersal, such as habitat loss, will only decrease range size, possibly contributing to amphibian population declines in the future (op.cit).
Figure 1 Projected amphibian species losses (no dispersal) and gains (unlimited dispersal) in Italy, Girardello et al (2010).
Unfortunately, it appears likely that during the time leading up to 2050, habitats will be further fragmented and destroyed. This does, however, assist current conservation, indicating that to aid the persistence of amphibian species; both existing and potential habitats must be protected and managed in a way that will allow optimum dispersal. Given that the current conservation status of 32% of known amphibian species is either ‘threatened’ or ‘extinct’, understanding their relationship with climate change is vitally necessary (http://www.iucnredlist.org/ initiatives/ amphibians/ analysis). There are various ways in which a changing climate could affect the status of amphibian species, through both direct and indirect methods. For climate to have a direct negative effect, the levels of temperature, moisture and UVB (ultraviolet-b) radiation would need to exceed the lethal limit of a given species (Carey & Alexander, 2003). Although recent studies have shown a correlation between amphibian declines and climate change, there has been little evidence to suggest that amphibians have been subjected to lethal levels of environmental variables (op.cit; Corn, 2005). There are a number of ways in which climate change could indirectly affect individuals. Successful breeding is essential to ensure the survival of any species. It has been suggested that climate change could interfere with reproduction by causing breeding to occur earlier. Tryjanowski et al (2003) found that the first spawning dates of R.temporaria and Bufo bufo shifted 8-9 days earlier between 1978 and 2002; correlating with warmer spring temperatures. This could be both detrimental and beneficial. It may provide more time for growth whilst reducing exposure to UVB radiation (Corn, 2005). On the other hand, it could also cause exposure to extreme spring temperatures (op.cit). Whilst some studies have shown significant trends towards earlier breeding, there have also been a similar proportion of findings concluding that climate has no influence upon breeding time (op.cit). Disease has been positively identified as a major cause for amphibian declines, and climate change could potentially facilitate the spread of infectious diseases, causing species to become more susceptible (Lips et al, 2008). Chytridiomycosis is a disease caused by the fungal pathogen Batrachochytrium dendrobatidis, and has been responsible for amphibian extinctions (Carey and Alexander, 2003). However, Lips et al (2008) found no evidence that climate change is the cause behind outbreaks of this disease. The chytrid fungus most likely prefers cooler temperatures and requires an aquatic environment for transmission (Corn, 2005). Therefore, the current trend towards a drier, warmer climate is not likely to encourage outbreaks of this disease (op.cit). A second fungus, Saprolegnia ferax, has been reported to cause mortality in particular amphibian species. Bufo boreas appears to only be susceptible to this pathogen in the presence of UVB radiation. Kiesecker et al (2001) concluded that low levels of precipitation during El Niño southern oscillation years caused the embryos of B.boreas to develop in shallower water. This in turn exposed them to extreme UVB radiation and as a consequence, the fungus caused mortality (op.cit). Although the association between current amphibian declines and climate remains uncertain, future climate change will inevitably provide serious challenges for amphibians. Whilst many of these challenges can be scientifically predicted, predicting how species will react proves to be more complex. Unfortunately, only time will tell which species will survive and which species will fail to persist under the pressure of a rapidly change global climate.
3.0 Insects
Insects are the most abundant group of animals on the planet, making up two thirds of all described extant animal species (Stange and Ayres, 2010). Like amphibians, insects are ectothermic so are also strongly influenced by external temperature and other climatic factors. They are extremely important within natural ecosystems due to their position at the bottom of the food chain, and play vital roles in processes such as decomposition and pollination. Insects also have economic involvements, with some species acting as pests and vectors of diseases. Therefore, research focusing on how insects respond to climate change is beneficial for both the natural environment and human economy. Since the 1990s many studies regarding insects in connection to climate change have been carried out (Musolin, 2007). It is expected to exert powerful effects upon abundance, physiology and distribution, with effects becoming more prominent as the severity of climate change increases (Stange and Ayres, 2010). A change in the distribution of insects has been one of the most frequently reported responses (Musolin, 2007). Those species living in northern temperate regions appear to be expanding their range northwards or moving to higher altitudes (Maes et al, 2010). Such shifts in distribution have been recorded in a vast number of species. In the year 2000, the distribution of the Southern green stink bug (Nezara viridula) in Japan was found to have moved 70km further north of that recorded in the early 1960s (op.cit). Other Heteroptera species, such as those living in Southern Europe, have been recently discovered in the north, probably as a result of climatic variation (op.cit). In Britain, species of Orthoptera have also extended their range. The unusually warm summers of 1989/1990 caused the distribution of the long winged conehead (Conocephalus discolor) in north-western Europe to progress north and east (Cannon, 1998). The distribution of Lepidoptera has been well documented, owing to this group’s high fecundity and dispersal ability, allowing distribution to be followed over a relatively short time period (Roy and Sparks, 2000). Observations of Lepidoptera species have been carried out for over 20 years in Finland and prominent northern range expansions have been recorded (Stange and Ayres, 2010). With many distribution shifts having already occurred, it is relatively easy to predict how a warmer future will affect present insect distributions. Range expansion towards the poles is most likely to become increasingly common, as insects seek out new habitats. A change in geographical distribution is just one way in which climate change has influenced, and will continue to influence, insects. A broad range of additional climate change induced effects, revealed through recent studies, will most likely impact upon the future survival and fitness of many species. High temperature reduces the time that is needed for insects to raise their body temperature to the flight activity threshold (Beaumont and Hughes, 2002). As an outcome of this, there may be an increase in activities that rely upon flight, such as mate location and egg laying (op.cit). As a result, many of the predicted impacts upon butterfly species have been positive. However, other aspects of climate change, such as drought, may have undesired effects. Prolonged arid conditions can have a negative impact upon host plant growth and egg survival (Roy and Sparks, 2000). One of the most recognized changes observed in butterflies is advancement in their first appearance (op.cit). This has been observed in most British butterfly species, showing a strong correlation with elevated temperatures. It has been predicted that per 1ËšC temperature increase, the first appearance of butterflies could advance by 2-10 days (op.cit). Advances in appearance have also been demonstrated in other insect groups. One month advancement in the spring appearance of Heteroptera species was found in Japan, and was also a consequence of soaring temperatures (Musolin, 2007). Other responses noted in insects include behavioural responses in Heteroptera, though they haven’t been frequently discovered. In Italy, a large number of seed bugs entered urban buildings during the summer. Apparently, this was done in an attempt to escape the harsh high summer temperatures and to find more suitable conditions for aestivation (op.cit). The diversities of dragonfly, butterfly and grasshopper species are expected to decrease in Belgium, if the predicted climate scenarios for 2100 are correct (Maes, 2010). Mortality can be one of the direct consequences of temperature as insects have specie-specific upper and lower temperature limits. In peacock (Inachis io) and comma (Polygonia c-album) butterflies, the proportions of individuals reaching adulthood differed dramatically with varying temperature (Bryant et al, 1997). 60% survived at 15-30ËšC, 0% at 9ËšC and 20-40% at 34ËšC (op.cit). Whilst such implications of global climate change are worrying, there may be some potential benefits. Metabolic rate is expected to double with each 10ËšC increase and mortality due to cold temperatures during the winter many reduce (Stange and Ayres, 2010). An increase in insect abundance is most probable and can be supported by recent outbreaks such as the gypsy moth (Lymantria dispar) in Central Europe (Cannon, 1998). The extent to which insects are susceptible to extinction will depend partly upon their geographical location. Those inhabiting the tropics are likely to be most at risk as they are highly sensitive to temperature and are already living fairly close to their upper thermal limits (Deutsch et al, 2008). Population growth rates in the tropics are predicted to decrease by up to 20%, further reducing fitness (op.cit). Biological traits which will cause species to have a greater extinction risk include reduced dispersal ability and low temperature tolerance. (op.cit). Most species which possess such characteristics inhabit low latitude areas. Unfortunately, whilst tropical areas are the most vulnerable, they are also the parts of the world which harbour the greatest biodiversity. In comparison, those insects in mid-high latitude areas are expected to experience increased population growth rates (op.cit). At higher latitudes, organisms are living at temperatures that are cooler than their optimum temperatures, so global warming could potentially enhance their fitness (op.cit). It can be seen that much effort has been made in an attempt to understand the links between insects and global climate change, and research will continue to try and establish which species are of greatest conservation concern. However, a key consideration which will play a role in extinctions is the extent to which species will be able to adapt (Cannon, 1998). Unfortunately, this is tremendously complicated to predict and as a result, many studies often overlook, or some have even exaggerated potential evolutionary adaptations. During the quaternary period, large-scale fluctuations in climate occurred, but the insect fossil record provides no evidence for large-scale evolutionary change during this time (op.cit). Many studies have also focused heavily upon temperature effects and have poorly investigated how rainfall and moisture could impact insects. However, this is mainly due to lack of information, as making predictions about rainfall patterns is relatively difficult. It can be expected that climate change will increase the abundance and distribution of the majority of insects but it must be remembered that responses will be specie-specific and care must be taken to avoid over-generalising predicted responses. Effort must be made to enhance our understandings, whilst aiming to fill current gaps in knowledge.
4.0 Polar Bears
The polar bear is often regarded as a marine mammal. Although this animal is quite efficient at exploiting marine habitats, it cannot survive within marine waters. Therefore this large predator can be more appropriately referred to as a terrestrial mammal as it lacks the specific adaptations possessed by true marine mammals such seals. Arctic sea-ice is critical to the survival of polar bears, as they depend upon it for numerous aspects of their ecology (Sterling and Derocher, 1993). It acts as a substrate on which to make long distance movements, provides access to maternal denning areas and is a platform for mating (op.cit). Most importantly, the ice allows polar bears to hunt and feed upon their primary prey; ringed seals (Pusa hispida) and bearded seals (Erignathus barbatus) (Regehr et al, 2010). Therefore, changes to sea-ice habitat are expected to have a dramatic impact upon the survival and reproduction of individuals, ultimately affecting the status of the polar bear as a species. With global climate change well underway, changes to arctic ice have already been documented. Since 1978, 14% of the total amount of ice cover has already been lost (Derocher et al, 2004). Thinning of ice is occurring and sea ice is breaking earlier in the year and freezing later. It has been speculated that in as little as 100 years, the arctic ice cap may disappear completely (Sterling and Derocher, 1993). Numerous studies have demonstrated how changes in sea-ice, undoubtedly influenced by rising global temperatures, are causing polar bears to suffer as a result. Polar bears prefer to hunt on ice which lies over the continental shelf, as the waters here are more productive than arctic basin waters (Regeher et al, 2010). Therefore, longer ice free periods over this area could lead to reduced foraging success and in turn could impact survival and reproduction. Between 2001 and 2005, declines in polar bear survival were observed (op.cit). This observation was linked to longer ice free periods over the continental shelf. It forced individuals to spend more time hunting on ice situated over less productive waters and caused some to seek alternative prey on land (Stirling and Parkinson, 2006). In western Hudson Bay, Canada, the sea-ice now melts completely each year, giving polar bears no other choice but to spend a proportion of the year ashore (Regehr et al, 2010). Individuals on land suffer food shortages. Ice free periods in 2004 and 2005 were associated with rare behaviour (op.cit). There were incidences of cannibalism and even starvation, indicating the severity of food unavailability (op.cit). In addition, living on land increases the exposure to humans, further enhancing their risk (Sterling and Derocher, 1993). Research concerning female polar bears has produced somewhat disturbing conclusions. Not only are the weights of females decreasing (figure 2), reducing cub survival and reproduction rates, but it is expected that within 100 years most females in Western Hudson Bay will be unable to reach the minimum body mass required to rear viable offspring (Derocher et al, 2004).
Figure 2 Mean estimated mass of lone (and thus possibly pregnant) adult female polar bears in Western Hudson Bay,1980-2004 (dashed line indicates fit of linear regression), (Sterling and Parkinson, 2006).
Thinning of ice is also occurring due to climate change. Thinner ice moves more quickly which could mean that polar bears need to use more energy to stay in contact with their preferred habitats (Derocher et al, 2004). Ice of reduced thickness also breaks up more easily. It has been shown that polar bears completely abandon ice and move to land when the concentration of ice drops below 50% (Derocher et al, 2004). This is most probably due to the increased costs of locomotion which are associated with walking over fragmented ice (op.cit). Considering that ice is required for long-distance movements, changes in ice may influence the distribution of polar bears. Large areas of open water due to lack of ice in addition to strong currents, may function as barriers, preventing the movement of polar bears, as implicated in South-eastern Baffin Island and Eastern Beaufort Sea (Sterling and Derocher, 1993). Through the assessment of a variety of studies, it can be seen that the future for polar bears within the midst of climate change does not look hopeful. They are highly specialised mammals, are already listed as ‘threatened’ under the ‘US Endangered Species Act’ and their habitat is declining rapidly (Derocher, 2010). The population most at risk is that in Beaufort Sea, as it is experiencing severe nutritional stress. Drastic declines for this population are predicted and it may even vanish by the end of the century (Hunter, 2010). However, research has shown that there is still time to avoid such a scenario, providing effort is made to reduce greenhouse gas emissions. This indicates that the future of this species lies solely in the hands of policy makers, who have the supremacy to implement the nesseccary changes needed for not only the preservation of this species, but for many more too.
5.0 Birds
Local variation in climate has long been recognised as an important factor affecting birds, but addressing how they will cope with long-term global climate change has only recently been attempted (Crick, 2004). Migratory birds have been of great interest, and this isn’t surprising, considering that regular long-distance flights enable individuals to exploit various climates in different locations around the globe. Warmer winters are predicted to cause a slight increase in the number of short-distance migrant and resident bird species, whilst there will be a strong decline in the number of long-distance migrants (Lemoine and Böhning-Gaese, 2003). This will likely be due to the increased competition resulting from resident bird species benefiting from the warmer conditions (op.cit). Migratory birds are also thought to be affected by mistiming, a result of climate change. This is when birds fail to breed at the time when their main food supply is most abundant (Both et al, 2006). A study concerning the long-distance migratory pied flycatcher (Ficedula hypoleuca) showed that populations declined by 90% in 20 years as a consequence of this (op.cit). However, on a more positive note, it has been suggested that migratory birds are faced with a lower extinction risk that sedentary species, due to their high mobility (Sekercioglu et al, 2008). With the forecast of an intermediate climate change scenario (surface warming of 2.8ËšC), it can be expected that 5% of sedentary species will become extinct, compared to 1% of long-distance migrants (op.cit). Global climate change appears to be causing birds to lay their eggs earlier. Data derived from the ‘British Trust of Ornithology Nest Record Scheme’ revealed that 51 UK species showed trends towards earlier laying over a 25 year period (Crick, 2004). These trends were apparent throughout a variety of bird groupings including seed eaters, corvids and water birds (op.cit). The pied flycatcher exhibited an increase in egg and clutch size when eggs were laid earlier, indicating that warmer temperatures may be advantageous (op.cit). By the year 2080, it has been estimated that laying dates will be earlier for 75% of bird species (Crick and Sparks, 1999). This is a positive prediction as the advancement of laying dates suggests that birds are coping with temperature rises (Both et al, 2004). It may also mean that the incidence of mistiming may be reduced as the timing of hatching will be brought closer to that of peak food supply. In terms of distribution, elevational distribution shifts are probable. Pounds et al (1999) studied the mountain cloud forests of Costa Rica. It was shown that global warming had caused the average altitude at the base of the orographic cloud base to rise. This resulted in the colonization of previously cloud forest areas by birds from lower altitudes (Crick, 2004). There are concerns that such changes could have a detrimental impact upon some species. Through modelling in the UK it has been suggested that species such as the snow bunting (Plectrophenax nivalis) may contract their range or even vanish from current breeding areas in the mountainous zones of the Grampians, Scotland (op.cit). Sekercioglu et al (2008) undertook a study to discover the impact of elevational limitations on the extinction risk of land birds (87% of all bird species). It was found that limitations in elevation actually accounted for “97% of the probability of a species being in a World Conservation Union category of extinction risk” (op.cit). Using a model that combined elevational limitations and four habitat loss scenarios, it was predicted that 400-550 avian land species will be extinct and a further 2150 will be at risk, under an intermediate climate change scenario for 2100 (Figure 3 and Figure 4).
Figure 3 The number of world landbird species estimated to be extinct by 2100, on the basis of different surface warming estimates, three possible shifts in lower elevational limit and four Millennium Assessment habitat change scenarios (Sekercioglu et al, 2008).
Figure 4 The number of world landbird species estimated to be at risk of extinction (near threatened or threatened) by 2100, on the basis of different surface warming estimates, three possible shifts in lower elevational limit and four Millennium Assessment habitat change scenarios (Sekercioglu et al, 2008).
6.0 Conclusion
Although most responses to global climate change are expected to be specie-specific, potential distributional changes appear to be quite uniform. Northern distribution shifts are likely to become increasingly common as species seek cooler climates. Elevational distributional changes will also occur, though elevational limitations in birds may increase their extinction risk. Impacts may range from phenological changes such as earlier breeding, to mortality resulting from temperatures exceeding thermal limits. Insects could potentia
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