The Impact Of Climate Change Upon Biodiversity

The impact of climate change upon biodiversity

Introduction

The primary focus of this report is to provide awareness of the complexity of ecological responses to climate change. The difficulty of predicting the impacts of climate change upon biodiversity will be made evident with the exploration of a range of feedback mechanisms and interacting processes. Anthropogenically driven climate change has been asserted to be responsible for an array of biological responses. These include shifts in species distributions, changes to life history traits, as well as an array of phenotypic responses. These all have impacts upon important ecosystem services. Limitations to phenotypic plasticity across an array of species will also be explored. A range of methods for investigating the impacts of climate change upon biodiversity will be explored, with a critique of their limitations. Suggestions of potential future research will also be proposed. This report is limited in that it provides an overview of responses to climate change, however the impact upon individual ecosystem services are not explored in depth.

Drivers of climate change

Scientists assert, with extreme confidence that increasing atmospheric CO2 is the driver of ongoing climate change (IPCC Report, 2018 United Nations, 2018). This is supported by Occam s law of parsimony, which assumes that the simplest explanation, is the optimal explanation (Trevors and Saier, 2010). The greenhouse gas effect explains the correlation between the increase in carbon dioxide emissions and a rise in temperature (Figure 1). Indeed, CO2 has increased by 85ppm within the last 55 years, reaching 400pm in 2019 (NASA, 2019). The correlated increase in temperature has exacerbated biodiversity loss (He et al., 2018) and species extinction rates (De Vos et al., 2015). Indeed, the Anthropocene has been implicated as the cause of a continuous cascade of ecological changes and transformations of regional floral and faunal communities (Braje and Erlandson, 2013).

The importance of biodiversity

The maintenance of biodiversity translates to ecological stability (Cleland, 2011). Even species that do not appear to have a current function are important in maintaining a genetic reserve. This is critical for when the environment changes in the future (Fetzer et al., 2015). The greater variation available in the gene pool of a species, the higher the chance of species survival in the future (Fetzer et al., 2015). Indeed, the idea of species redundancy has been criticized for failing to take these concepts into account (Gitay, Wilson and Lee, 1996).

This understanding is important when making conservation decisions about the taxonomic level to focus on, regarding species conservation (Thomson et al., 2018). From a conservation perspective, the population level would be an ideal conservation unit, however limited resources may mean this is not always feasible (Mace, 2004). Biodiversity provides important ecological services such as crops, biofuel and medicinal plants. Biodiversity also provides regulatory services, including pollination, climate and disease regulation as well as soil for agriculture (Watson and Lovelock, 1983 United Nations, 2016 Shrestha et al., 2018 Ngo et al., 2019, IPBES, 2019b, 2019a).

Climate change disrupts these important ecological services (Breshears, L pez-Hoffman and Graumlich, 2011). Indeed, climate change has impacted every biome to date (Table 4. And 5., Appendix, Author, 2019). Biodiversity suffers from multiple, interacting pressures, Sala et al., (2000) asserts that the greatest drivers of a change in global biodiversity by the year 2100 are land use change, followed by climate change. Regions of high latitude and altitude have shown particularly sharp responses to climate change in terms of shifts in biodiversity (Theurillat and Guisan, 2001). Furthermore, climate change has been found to increase the spread of wildlife diseases and zoonoses (MasComa and Valero, 2008 Mills et al., 2010), as well as invasive species (Table 2, Author, 2019).

Further implications of climate change are expected, including alteration to habitats through sea-level rise (Rahmstorf, 2007), increased fire frequency (Mouillot et al., 2002), altered weather patterns (Hashim and Hashim, 2016) and direct warming of habitats (Eaton and Scheller, 1996 Warren, et al., 2001). Responses to climate change Changes in life history traits due to climate change The study of the impact of increased temperature upon life history traits, allows comparison across a range of taxa (Pecuchet et al., 2018). The alteration of life history traits such as adult size, development time and growth rate, may allow adaptation to climate change (Nylin and Gotthard, 1998 Pacifici et al., 2017). Changes in life history traits, as a response to temperature may be explained by the metabolic theory of ecology (Clarke, 2006). Metabolic rate increases with temperature, this is explained by the fact that cellular biochemical reactions occur more rapidly with increasing temperature (Clarke, 2004).

This finding is known as the Boltzmann factor (Blundell and Blundell, 2009). Indeed, a thermal sensitivity index, known as the Q10 calculates the factor by which metabolism and other biochemical reactions increase when temperature is increased by 10 degrees Celsius (Del Rio, 2010).

Bergmann`s rule, predicts that organisms will exhibit a smaller body size in warmer climates (Teplitsky and Millien, 2014). This concept has been extended to predict that body size will decrease with increased temperatures induced by climate change, as found to be the case by Del Rio, (2010) and Tseng et al., (2018).

These findings have implications for commercially important species which are predicted to decrease in size with further climate change, including the common carp Cyprinus carpio (Daufresne et al., 2009 Weber et al., 3 2015). Indeed, Tseng et al., (2018) argue that a new hypothesis should be developed, to describe and explain the relationship between body size and temperature. This is supported by Gaston et al., (2008), who assert that, a novel synthesis of biogeographical patterns, and the interaction of these patterns, is overdue. Species-range shifts Ecological responses to climate change are vast, indeed (Walther et al., 2002) argues that impacts have been found from the poles to the tropics, across a wide range of species and communities. Each species has a unique thermal tolerance, which determines its latitudinal range (Sunday et al., 2012).

Alterations in global temperatures are followed by range shifts of many species, notably the most thermally sensitive taxa, such as amphibia, and lepidoptera (Paaijmans et al., 2013). As such, these species are more likely to experience changes in phenology, as well as a Northward shift in their range (Valtonen et al., 2014). Ungulates are another thermally sensitive taxa (Brivio et al., 2019). Biotic shifts are argued to be more profound between mid to high latitudes, since warming has been more pronounced in these areas (Dillon et al., 2010). Furthermore, Wilson et al., (2005) asserts, that not only a Northward shift in range of many taxa is likely, but also an elevational shift of thermally sensitive species. Vegetational shifts have also been recorded in Switzerland, where an increase in exotic species have been observed, correlating with milder temperatures (Figure 2, Walther et al., 2002). Furthermore, changes in vegetation may lead to hydrological changes, affecting aquatic species (Bosmans et al., 2017).

Phenotypic plasticity as a response to climate change Temperature has an impact upon biodiversity, across all scales, from the molecular scale, at the level of nucleotide structure to the scale of the biosphere (Mieszkowska et al., 2013). Organisms may adapt to climate change through phenotypic plasticity, which refers to the ability of an organism to respond to the environment (Williams et al., 2008 Hoffmann and Sgr , 2011a Wong and Candolin, 2015). Indeed, phenotypic plasticity has been asserted as being under genetic control (Nicotra et al., 2010).

However, this is a simplified explanation, as genes may be switched on or off through DNA acetylation, or methylation respectively, adding a layer of interaction between genetics and the environment, known as epigenetics (Duncan et al., 2014). Indeed, animals may disperse, adjust through phenotypic plasticity, or adapt through genetic changes (Wong and Candolin, 2015). Examples of forms of phenotypic plasticity in response to climate change are illustrated in Table 1. (Author, 2019). Impacts of a warming climate have been argued to be particularly pronounced at the poles (Dillon, Wang and Huey, 2010 Iverson et al., 2014 Blix, 2016), and therefore it is expected that species of the poles require the greatest phenotypic response to climate change.

Phenotypic plasticity may be described in terms of an individual s genotype exhibiting the ability to show plasticity, followed by a phenotypic response (Ghalambor et al., 2007 Evans and Hofmann, 2012). However, plasticity itself, has been argued to be under selective pressure (Price et al., 2003 Ghalambor et al., 2007). This means that selection will favour individuals that have an ability to show plasticity in their response to climate change (Price et al., 2003). It has been estimated that organisms within the tropics, will be required to increase their metabolic rate to the greatest extent. This is in order to adapt to increased temperatures, which have a non-linear impact upon metabolism (Dillon et al., 2010). However, there are limitations to an organism s ability to adapt, since all individuals possess physiological and metabolic constraints (Dillon et al., 2010)

Ecological feedback mechanisms

The Earth has been proposed to self-regulate, and biodiversity itself has been argued to be fundamental in this self-regulation (Watson and Lovelock, 1983). Indeed, in 1982 James Lovelock proposed the Daisy world model, to illustrate how the Earth itself could be considered akin to a self-regulating organism (Watson and Lovelock, 1983 Lenton and Lovelock, 2000).

This model conceptualises the impact of both positive and negative feedback mechanisms upon the Earth. This may be utilised to demonstrate the positive feedback of carbon dioxide concentrations within the atmosphere, as well as within the oceans and may describe the mechanisms underlining the concept of runaway climate change (Goldblatt and Watson, 2012). Boysen, et al., (2017) also argue that climate may limit the ability of some geographic areas to store carbon dioxide.

Furthermore, climate change may lead to habitat fragmentation (Oliver et al., 2015) as well as an increase in invasive species (Kueffer and Daehler, 2009). Climate change may also lead to a change in the typology of a landscape and associated albedo, which has been found to impact the climate (Pielke et al., 2002) incurring novel interactions of environmental variables and potential feedback mechanisms (Zeng and Yoon, 2009). An example of a negative feedback mechanism includes carbonate compensation, which increases the pH of the ocean as a response to ocean acidification (Tyrrell, 2011 Boudreau et al., 2018a).

Ocean acidification is caused by an increase in carbon dioxide absorption by the oceans and results in the breakdown of the calcium carbonate exoskeletons of coral and mollusk species (Tyrrell, 2011., Table 2, Author, 2019). As a response to the increased acidity of the ocean, weathering of calcium carbonate rock, deep in the ocean, releases an alkali solution, returning the pH closer to the set point (Boudreau et al., 2018a).

Meanwhile, an example of a positive feedback mechanism is the impact of an increased temperature upon the decomposition rate of soil microbes (Davidson and Janssens, 2006). However, an increase in temperature is also associated with an increased productivity of vegetation and associated carbon, which may exceed decomposition rate, providing a negative feedback mechanism (Davidson and Janssens, 2006). This provides an example of the complexity of estimating the impacts of climate change upon biodiversity.

Methods for studying the impact of climate change upon biodiversity

Species interactions may be complex, making accurate predictions difficult, due to the fact that a range of variables are at play (Table 3). Dieleman et al., (2015) modelled the possible impact of increased temperature and precipitation, through climate modelling upon sphagnum spp. of Northern peatlands. Using methods of predictive modelling, Dieleman et al., (2015) asserted that a predicted increase in temperature and precipitation would likely result in an expanded range of sphagnum spp. in the short term. However, the study appears to have failed to consider the complex interactions between atmospheric carbon dioxide levels and soil enzymes, involved in carbon decomposition (Freeman et al., 2001). For example, a shortage of oxygen and low temperatures have been found to reduce the decomposition rate of peatlands by inhibiting an enzyme (phenol oxidase) involved in the decomposition process (Freeman et al., 2001). Indeed, Pinsonneault et al. (2016) assert that temperature is the dominant variable affecting the rate of phenol oxidase activity, with pH and nutrient availability having a lesser impact on the variance of enzyme activity.

Solutions for biodiversity

Although current U.K. climate change proposals offer an optimistic goal of reducing greenhouse gas emissions by at least 80% of 1990 levels by 2050 (Committee on Climate Change, 2008), they neglect to consider the need for ecological restoration and habitat connectivity in the face of habitat loss and degradation (MacArthur and Wilson, 2001a). For example, the Committee on Climate Change (2018) asserts that A fifth of farmland must be turned into forest, peatland or used for biomass crops , in order to reduce carbon emission to net zero. Arguably, agri-environmental policy is an area which has a powerful potential to impact not only biodiversity, but also carbon dioxide emissions through carbon sequestration. For example, currently land abandonment is not rewarded financially through the common agricultural policy (Merckx and Pereira, 2015a).

The land sharing vs land sparing debate is an important consideration when considering agri-environmental policy (Figure 3., Table 6., Appendix, Author, 2019). Of the two, land sparing has been found to allow a greater array of taxa to persist (Green et al., 2005). This has led Merckx and Pereira, (2015c) to argue that a two tier agri-environmental scheme with a focus upon increasing agricultural yields of fertile land alongside land sparing for biodiversity is optimal for not only agricultural but yields, but also biodiversity. Furthermore, it is also important that spared land is connected through habitat corridors (MacArthur and Wilson, 2001b Holt, 2003) to allow dispersal and to maintain genetic diversity across populations (Mech and Hallett, 2001). Research on the optimal habitat type for soil carbon sequestration should also be considered (Ostle et al., 2009).

Conclusion

The primary focus of this report is to provide awareness of the complexity of ecological responses to climate change and in predicting the impact of climate change upon biodiversity. This report is limited in that it provides an overview of responses to climate change, however the impact upon individual ecosystem services are not explored in depth. However, this report has explored a wide range of responses of biodiversity to climate change. Yet, critically, there are limits to adaptive phenotypic plasticity (DeWitt et al., 1998 Murren et al., 2015). Furthermore, it is not always possible for species to adapt, leading to increased extinction rates (De Vos et al., 2015).

In terms of solutions for promoting biodiversity against the backdrop of climate change, it is important to consider, not only the reduction of carbon dioxide emissions, but also the ecological restoration of important habitats, including the maintenance of habitat corridors (MacArthur and Wilson, 2001a).

Land sparing has been found to lead to greater biodiversity than land sharing. In light of this, a two tiered system of agri-environmental schemes has been proposed by Merckx and Pereira, (2015), which would allow financial incentives for 13 land abandonment as well as wildlife friendly farming . Initiatives for land sparing would be particularly beneficial for increasing the degree of carbon sequestration of these habitats. Furthermore, research on the optimal habitat types for soil carbon sequestration should also be considered (Ostle et al., 2009).