Climate change and the destruction and degradation of habitat due to anthropogenic land-use change are both key threatening processes driving the global loss in biodiversity. Despite this, we currently have very little understanding of how land-use change and climate change interact with each other to drive impacts on biodiversity. If the combined effects of climate change and land-use change are greater than the effects of each threat individually, current conservation management strategies may be inefficient and at worst ineffective. Therefore, there is a pressing need to identify whether interacting effects between climate change and land-use change exist and, if so, how to best minimize negative impacts to biodiversity as a result of these interactions.
In this thesis I use a mix of modelling approaches to gain insights into the interacting effects of climate change and land-use change on biodiversity for decision making. In Chapter 2 I present a global meta-analysis of studies that quantify the effect of habitat loss on terrestrial biological populations and examine whether the magnitude of these effects depends on current climatic conditions and historical rates of climate change. My results show that current climate and climate change are important factors determining the negative effects of habitat loss on species density and/or diversity. Habitat loss and fragmentation effects are greatest in areas with high maximum temperatures. Conversely, they are lowest in areas where average rainfall has increased over time. This highlights that areas at physiological limits for species are particularly susceptible to the synergy of global change drivers.
In Chapter 3 I use the same model of the interactions between habitat loss and climate as in Chapter 2 to quantify the implications of these interactions for loss of biodiversity due to habitat loss at the global scale. I find that climate change will exacerbate the risk of global terrestrial mammal and bird declines due to future land-cover change by 9-43%. I also discover that the ranking of global biodiversity hotspots (regions of exceptional biodiversity value) in terms of threat from land-cover change depends critically on the interactions between climate change and habitat loss. This highlights the need for more global biodiversity response studies to consider climate change interactions if we are to develop effective conservation policies and strategies. Furthermore, if we ignore the role of interactions during the prioritisation of conservation areas, we will substantially underestimate impacts in many regions and make conservation prioritisation decisions that are highly sub-optimal.
In Chapter 4 I build a Bayesian Belief Network to quantify the independent and combined effects of climate change and urban growth on freshwater macroinvertebrates and fish in South East Queensland (SEQ), Australia. I find little change in richness averaged across catchments, but identify important impacts and effects at the finer scale. High nutrients and high runoff as a result of urbanization interacted with high nutrients and high water temperature as a result of climate change, and is the leading driver of potential declines in macroinvertebrates and fish at fine scales. By identifying these mechanisms behind predicted biodiversity loss, I was able to identify management strategies that can simultaneously tackle both climate change and land-use change. The good news story that came out of this study was that I identified riparian vegetation restoration as an important adaptation tool that can mitigate the negative effects of climate change and land-use change on freshwater biodiversity.
In Chapter 5 I present a decision making framework for optimally allocating conservation dollars to different management actions for the conservation of freshwater biodiversity in SEQ under climate change, land-cover change and their combined effects. My results show that channel restoration (i.e. the protection, rehabilitation and/or restoration of riparian vegetation/zones) as a single management strategy can provide the greatest overall protection of macroinvertebrate and fish richness in response to climate change and/or urban growth. I also reveal that farm/land management (i.e. management of pesticide and fertiliser inputs, burning practices and livestock grazing) and channel restoration together can provide the greatest conservation benefits if decision-makers are limited for resources.
My final chapter serves to synthesize and interpret this research for the recommendation of management and policy responses. Through comprehensive analyses I have shown that the consequences of interactions between climate change and land-use change are generally unfavourable for species persistence and their impacts will become even more pervasive in a changing world. A paradigm shift in conservation planning is therefore required to include more proactive planning if we are to avoid or mitigate the interacting effects of climate change and land-use change on biodiversity. This research will assist Governments, Non-Government Organisations, and other conservation-minded people in developing and achieving effective climate change mitigation and adaptation programs.