Disentangling the complexity of climate change and land-management effects on wildlife communities

As the climate is changing, wildlife species and communities often shift towards high latitudes, among other possible responses (Pecl et al., 2017). However, such climate-driven latitudinal shifts are often mediated, hindered or facilitated, by other forces. Such forces materialize at different scales, from regional to continental level, such as ecological barriers (Marjakangas et al., 2023), to local scale, such as land-use and habitat management (e.g. Thomas & Gillingham, 2015). The study by Gaget et al. (2023) uses a long-term dataset from non-breeding water bird surveys to answer a topical question: Under climate change, do distribution shifts of hunted duck species differ from those of non-hunted (and other hunted) species? The prediction was that local-scale hunting habitat management would increase the site fidelity of hunted species, thereby hindering their climate-driven latitudinal shift as compared to non-hunted species. The authors apply a widely used community-level approach (Devictor et al., 2008) to quantify the overall response to climate change. The approach is based on combining site-level survey data with species-specific temperature index (i.e. the average long-term temperature experienced by the species across its range) to derive a community-weighted mean thermal affinity (i.e. an index representing the balance between warm and cold-dwelling species; Devictor et al., 2008). The authors are then able to trace the individual contribution of each species to the community shift and relate this contribution to species-level traits. While the broad pattern of community-level shift following climate change has been widely demonstrated, this research is the first to reveal that hunted duck species appear to be less inclined to shift their distribution in response to climate warming compared with non-hunted species (Gaget et al., 2023). This highlights the broad potential impacts of anthropogenic interventions on wildlife communities which may not only facilitate shifts under climate change, but also hinder them. Hunting habitat management, often based on managing habitat to increase the food base for plant-eating waterbirds, is thought to be rather common in the study region, South-Western Europe. This intervention may boost winter site fidelity for waterbirds, thereby explaining the pattern found. Indeed, rather convincingly, all of the hunted plant-eating species considered in this study had a negative contribution towards the overall community shift (Gaget et al., 2023). That is, they hinder the community adjustment to climate change.

This research provides two main pointers for discussion regarding future applied research lines, with wide implications for biodiversity conservation under global change. Firstly, it indicates the potential effects of a persistence strategy, whereby a habitat is managed to aid the persistence of a species, or community, rather than facilitating shifts in response to climate change. While empirical evidence on the effects of a facilitation strategy is relatively large (e. g. Thomas & Gillingham, 2015), the persistence strategy has been much less studied. Understanding the effects of these two strategies, and the context in which they may be most relevant, will be pivotal to aid species adaptation to climate change in the Anthropocene. For example, at the northern edge of land masses, such as in the Boreal biome, northern species may have limited terrestrial land with potential habitat expanding northwards under climate change. In these conditions, a persistence strategy may be more adequate for enhancing the viability of the whole community. Indeed, in Finland the network of national protected areas, largely focused on preserving old-growth forests and mires, was found to aid the persistence of cold-dwelling northern bird species that would have almost nowhere to go farther north (Santangeli, Rajasärkkä, & Lehikoinen, 2017).

Secondly, from a methodological perspective, while the findings by Gaget et al. (2023) align with the authors' initial predictions, the evidence remains correlative. The pattern, low shift of hunted ducks under climate change, may not be solely attributed to hunting, but to other confounders (e. g. nearby rice fields and other land uses, as the authors suggest). This strongly calls for the use of rigorous impact evaluation designs based on a counterfactual approach (what would have happened in the absence of an intervention; Ferraro, 2009). Practically, a site-level analysis would be possible if the sites could be classified based on their focal management, for example managed for hunting or not. Such data, while currently unavailable, could be potentially gathered in the field during the surveys, or via questionnaires sent to the bird counters. While such an endeavour may sound challenging, a similar effort has been successfully completed to collate a database on management effectiveness for the world's protected areas. A matching approach could then be implemented using the new site-level information (Wauchope et al., 2022). By matching sites managed for hunting with otherwise similar (with respect to environmental, socio-economic and other factors) sites which are not managed for hunting, the effect of potential confounders on the treatment (in this case hunting management) and on the outcome of interest (in this case waterbirds occurrence) would be minimized. Consequently, the resulting evidence on the effects of hunting habitat management would be much stronger (see e.g. Wauchope et al., 2022; Santangeli et al., 2023). In the field of conservation impact evaluation, such counterfactual approach is gaining momentum, enhancing our ability to deeply understand the real impact of interventions (Baylis et al., 2016).

Overall, in order to achieve effective species conservation and management under interacting pressures from climate and land-use change, strong evidence on the relative contributions of the key drivers will be paramount. Such evidence will need to be available at different levels, from species to communities, for different strategies, and across spatial and temporal scales. The study by Gaget et al. (2023) provides a valuable contribution towards understanding how management can mediate community-level shifts under climate change, filling a gap for the seldom-tested strategy based on persistence. However, much work is yet to be done, starting from mobilizing the information needed for assessing the effectiveness of interventions. The urgency imposed by unprecedented global change, and the scale and impacts of hunting (e.g. Pérez-García et al., 2023), both regulated, unregulated and illegal, call for more research and conservation efforts on this practice.