1. Specialized habitat requirements. Species with widespread and unspecialized habitat requirements are more likely to be able to endure a greater intensity of climatic and ecosystem change than those specialized species. Even though if such species are able to spread to new climatically fitting environments, the probability of satisfaction of all their habitat requirements are low, such example of species are European bats (Rubelo 2010). Susceptibility is aggravated where a species has a number of life stages, each with different habitat or microhabitat requirements, tadpoles for example or when the habitat or microhabitat to which the species is specialized is particularly weak to climate change impacts such as the Polar Regions. In some cases, severe specialization may permit species to avoid the full impacts of competition from local or invading species. Therefore, the interaction of such characteristics with climate change must be thoroughly considered for each species group determined.
2. Limited or low environmental fortitudes or thresholds that are likely to surpass at any stage in the life cycle due to climate change. The ecology and physiology of many species is tightly attached to particular ranges of climatic variables such as precipitation, temperature, pH and carbon dioxide levels, and species with little tolerance ranges are exceptionally vulnerable to climate change. Even though species having both expansive environmental tolerances and unspecialized habitat requirements may already be close to its limit beyond which ecological physiological tasks, such as protein and enzyme functions in animals quickly breaks down.
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3. Dependence and reliance on specific environmental cues or triggers that is likely to be interrupted by climate change. Many species depend on environmental cues or triggers for breeding, egg-laying, migration, germination of seeds, hibernation, spring emergence and a series of other vital and essential processes. Some cues are unaffected by climate change, such as day length and lunar cycles, but others such as temperature and rainfall, including their interacting effects will be seriously impacted upon by climate change. Species would become exposed to changes in the timing and scale of these cues when they started to lead in uncoupling with other essential ecological processes, for example, early spring warming initiates the emergence of a species prior to their food sources being available. Climate change susceptibility is made more complicated when a species' life history has different stages or different sexes depend on different cues. This in fact, changes the morphology, behaviour and physiology of affected species.
4. Having interspecific interactions that are liable on being disrupted by climate change. Many species' interactions with their hosts, competitors, symbionts, pathogens and preys would be affected by climate change. This could either be due to the regression or loss of resource species from their dependent species' vicinity or loss of organization in the timing of biological events - phenology. These species which are dependent on interactions that are highly vulnerable to disruption by climate change are at a high risk of extinction, specifically where they have high level of specialization for the specific resource species and are most unlikely to be capable to switching to or substituting other species.
5. Poor capability to migrate, disperse to or to colonise a new or more suitable areas. Generally, in response to climate change, the more particular likeable environmental conditions on which each and every species is adapted - bioclimatic envelope, would shift northwards and to increasing altitudes. Species such as land snails and ants, having low rates or short distances of dispersal, would most probably to unable in migrating fast enough to keep up with the continuous shifting climatic envelopes. As their habitats become bare and exposed to gradual increase of climatic changes, they would face increasing extinction risk.
Although species which managed to disperse to more newly suitable bioclimatic areas and escaping from climate change, there would still be several other factors which may affect the success of colonization. Species' phenotypic plasticity - ability to change its phenotype in response to its environment and genetic diversity would determine the odds of adaptation over various time scales. Where they exist, information could be supplemented from direct measures of genetic variability. Such obtainable information are on naturalization outside species' local ranges and on the achievement of any past translocation. Foreign factors which are likely to decrease success of dispersal include the presence of geographic barriers such as mountain ranges, rivers and oceans, whereas for marine species, ocean currents and temperature gradients. Anthropogenic alteration of migration paths or destination habitats would increase species' susceptibility to negative impacts from climate change.
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In the 20th century, there has been a distinct impact of climate change, mainly in the increase of temperature, on biological systems. The change, either it being anthropogenic - resulting from human activities or natural, has been observed in many parts of the world and is consistent with the effects of temperature changes in the different regions. The possibility that the observed changes following an expected direction happened by chance alone is insignificant. Such systems, for example, include the timing of migration events, species distribution and population size. These observations link regional climate change as the leading contributing factor. Different intensity and frequency of disturbances, such as fires, droughts; that are affected by climate change have been observed and they have been found as affecting the productivity and species composition within an environment. Particularly in forested systems, the incidences of pests and disease outbreaks have also changed and can be linked to changes in climate. Other extreme variable climatic events such as tropical cyclones, floods, hail; and the consequences of some of the events - wildfire, land erosion; have upset ecosystems in many parts of the world. This could also impact human population if areas which are being relied upon, such as forests or wetlands were destroyed by climatic events.
It has been observed that climate change is linked with changes in species distribution. Possible shifts associated by climate in animal ranges and densities have been distinguished almost on all continents, the polar regions and even within major taxonomic groups, for example:
Due to climate change and also land-use pressure, there is growing evidence of invertebrates such as butterflies (Hill 1999, Parmesan 1999) shifting its distributions. Insects are known as being poikilothermic with high reproductive and dispersal rates. As an example, as temperature increased, butterflies in North America and Europe have been found to migrate northwards as the environments are more suitable for colonization. In UK, a study was done on the distribution change of the speckled wood butterfly, Pararge aegeria (Jane Hill 1999). It has shown that the butterflies have expanded its northern margin substantially since 1940 (Emmet & Heath 1990).
Since millions of years ago, extending to the age of dinosaurs, marine turtles have been one of the species that have survived many dramatic climatic changes. At present, in response to the continuous change of climate and increase of sea levels, marine turtle populations have acquired new routes for their migration and their breeding sites are more redistributed and reallocated. They have the ability to properly adapt to climate change but only to a certain level, before it becomes a threat to their survival.
Increasing Temperatures on Nesting Beaches
Marine turtles are sensitive creatures characterised as temperature dependent sex determination, on which the sex ratio of the hatchlings are influenced by the temperature experienced during their incubation. For turtle eggs to hatch properly, they require a thermal tolerance range nest temperature varying between 25°C to 35°C (Ackerman, 1997). Female offsprings would be predominantly produced at high temperatures and males at lower temperatures (male:female = 1:2 to 1:3) (Ackerman, 1997). Figure 4.2 shows the correlation between incubation temperature and percentage of female hatchlings for four turtle species. With increasing temperatures, there would be more chances of obtaining a higher ratio than norm of female marine turtles to male. In Eastern Malaysia, some of the nesting beaches have been altered too much by man-made changes causing the environment to be in a range of temperature where only female hatchlings were produced (Chan 1996). This drastic phenology change could lead to more adult females laying unfertilised or low amount of eggs, leading to the lost of annual quantity of hatchlings.
In some tropical areas, although the season wasn't summer, sand temperatures at nesting beaches have approached or exceeded the lethal limit of egg incubation. This is usually due to the air temperature which has a strong correlation with the sand temperature (Haysetal 1999). In some tropical beaches in northern Australia, some marine turtles nest during winter or they nest on cooler beaches.
Consequently, there are also certain other factors that influence the determination of hatchlings' sexes. For example, the temperature of the incubation may differ throughout the season, the placement of the nest - nest nearer to the ocean may have a greater possibility of tidal barrage leading to erosion while nests further inland would risk to a greater possibility of drought and predation, how shaded the nesting area is under, beach nourishment (Crain et al. 1995) and events such as heavy rain with the depth of the eggs (Mrosovsky et al.1988).
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During the first decade of 1968, the time when marine turtle studies were commenced, within the southern part of the Great Barrier Reef, the depth of the turtles' nests' sand temperatures were never recorded as reaching the lethal temperature. But since the abnormally hot summer due to El Nino during December 1997 to January 1998, nests at beaches of Mon Repos, Australia has now reached to as high as 36°C and it sometimes continued for weeks until hatching season. As a result, there has been an increased death of eggs or defects on the new hatchlings. In the future, if there is a further increase of temperature during incubation to hatching season, it could be predicted that the success of emerging normal and healthy hatchlings would decrease tremendously, thus simultaneously decreasing the population and distribution.
Natal homing hypothesis, invented by Carr (1967) stated that adult female turtles would return to the beach on which they were born in order to breed - a behaviour which implies the turtles being 'faithful' to a specific location. This hypothesis was further supported by genetic evidences (Meylan 1990, Encalada 1996). However, by observing the tracks of a number of female loggerhead turtles, Caretta caretta, it was concluded that they relocate their areas of breeding sites when the environmental conditions are unstable (Daniel W. Wood 2000, JOSEPH B. PFALLER 2008). Relocating eggs is a common strategy used by marine turtles and other reptiles such as crocodiles (Thorbjarnarson et al. 1992) in order to conserve their declining populations around the globe. Marine turtles reallocate new breeding sites in response to changes in cues from the environment such as beach stability, ocean current and sea temperature. Certain temperatures could cause turtles to undergo selective pressures, thus creating nests on cooler areas such as on temperate beaches instead of tropical beaches or during winter rather than summer. Hatching in winter and being exposed to the cold temperature could be lethal to the new turtles as they are at risk of chilling injury (Costanzo 2008).
Climate change, and competition of coastal land by humans for economic purposes or settlement, has caused the small islands such as those in the Caribbean, the Maldives, the Pacific and the Great Barrier Reef to be in a huge threat (Huang 1997) of sea-level rise, mainly because of their small size, over-reliance on coastal sources and high population density (IPCC 2001a). This can cause physical impacts such as coastal flooding, increase coastal erosion and land loss (Klein & Nicholls 1999). Thus, damaged nesting habitat would increase mortality of eggs and eventually loss of nesting beaches. Turtles in loss of their nesting beaches have to seek out new nesting areas, leading to scattering in distribution from their original paths.
Climate change, and if combined with other factors caused by humans either in affecting nesting success - pollution, artificial lighting, coastal defences (Witherington 1992, Katselidis & Dimopoulos 1998) or adult population - overfishing, disease; could lead to unstable marine turtles distributions. Within years, if no distinguish precautions are taken; marine turtles would be under greater threat and one day would extinct.
Young turtles mainly feed on plankton as their diet in the ocean but the distribution of plankton is not consistent around the ocean as they are easily affected by change of sea surface temperature. Plankton richness on the open ocean varies in time and location in response to temperature and ocean currents - both influenced by climate change. Therefore young turtles would migrate to areas of high plankton abundance, which are usually northwards.
Increasing sea temperature will distress the degree of physiological function of marine turtles as they are poikilothermic - blood temperature fluctuates according to their surroundings. Warmer habitat increases their metabolic rates as well as their growth rates, resulting to immature turtles being produced. With the current trends of climate change, it is expected that extreme hot summers that have taken place in recent years would be more common. Coral reefs would be negatively impacted as the heat causes coral bleaching. For some seagrass species, the temperature could be lethal and this would cause reduction in marine field quality and food source for other species, marine turtles included. The damage could take years for coral reefs to heal and seagrass to renew. Depleting food source for the turtles over years would decrease growth rates for immature turtles and decrease levels of adult female to prepare for breeding journey.