Jellesmark, Sean; (2022) Measuring the impact of conservation on species' populations. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The global biodiversity crisis has sparked a rise in conservation actions. However, the impact of conservation actions on species’ populations is often not evaluated. In particular, studies of the impact of large-scale conservation, such as area protection or national legislation aimed at safeguarding biodiversity, on population trends remain poorly represented in the scientific literature. The resulting limited knowledge of conservation effectiveness potentially hinders effective evidence-based decision making and leads to suboptimal conservation outcomes. Here, I collate longitudinal records of vertebrate abundance, conservation interventions and ancillary information to measure the impact of conservation on species’ populations across different spatial and temporal scales. Specifically, I estimate the impact of lowland wet grassland reserves on breeding trends of wading birds in the United Kingdom by creating counterfactual reserve trends from national monitoring records collected by volunteers. This demonstrates that lowland wet grassland reserves have a positive impact on targeted species of wading birds. To understand the drivers of breeding abundance within these reserves, I combine local management records with climatic variables and breeding counts and use a Bayesian mixed modelling framework to estimate the association between conservation actions, site-specific conditions and annual breeding abundance for four wading bird species. The resulting estimates show that breeding abundance associates with different factors for the four species and provides new information on conservation effectiveness that can be used to inform local reserve management. Last, I explore the impact of conservation actions on trends in vertebrate populations worldwide. I categorize conservation actions for more than 26,000 populations, create counterfactual population indices representing how populations may have developed in the absence of conservation, calculate the impact of conservation on a global population index, and estimate how specific conservation actions relate to population changes. I show that conservation benefits targeted vertebrate populations, that in the absence of conservation, a global index of vertebrate abundance could have declined in addition to what is currently observed and that, in particular, conservation through species and land & water management has a positive impact on targeted populations. The methods developed and applied in this thesis demonstrate how to estimate the impact of conservation actions on species’ populations. This work also highlights the potential of longitudinal abundance records for evaluating conservation impact and emphasizes the importance of large-scale monitoring programmes.

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