Towards closer integration between ecology and evolution

Developing deeper links between ecology and evolution is not a new idea and has been advocating since at least the 1950s (Futuyma, 1986), but most 20th-century attempts can be considered more as rapprochement than actual integration (Huneman, 2019 for a detailed historical review). However, based on early isolated insights (e.g. Antonovics, 1976; Pimentel, 1961), the idea has been revivified over the last two decades, around the concepts of eco-evolutionary dynamics and feedbacks (Hendry, 2017). Significant efforts have indeed been made to percolate concepts and ideas between the two fields, especially across biodiversity levels (e.g. Hendry, 2017; Leibold & Chase, 2017; Loreau, 2010; Vellend, 2016), even if (i) more has been done at the population to community level than for higher levels of ecological organization (e.g. including ecosystem functioning) and (ii) analyses of reciprocal feedbacks remain rare compared to mainstream research in either field.

The number of studies claiming to be ‘eco–evo’ has risen sharply (Bassar et al., 2021), even if most of these studies actually represent classical ‘eco’ or ‘evo’ approaches, raising the question of what eco–evo really is. The definition proposed by Bassar et al. (2021; see also Hendry, 2017, chapter 1) may serve as a baseline, built on the assumption that ecological and evolutionary processes occur at the same timescales because this allows for true eco-evolutionary dynamics (EED) and feedbacks. Fast global change (e.g. temperature increase; IPCC, 2023) leading to enhanced selective pressure is certainly a good reason for considering such EED, highlighting the fact that fast evolutionary dynamics can match fast environmental change (and fast biodiversity loss; Diaz & Malhi, 2022). From this definition, the debate can (and must) develop to integrate concepts, ideas and practices of ecology and evolution into EED, and this is what is proposed in this special issue (general outline in Figure 1), revivifying this debate by considering several themes: the first relies on biodiversity itself, with the idea of including all biodiversity levels (from molecule to biomes), all branches of the tree of life, and some overlooked aspects of variability. The other themes are concerned with extending the temporal (and implicitly spatial) frame in which biodiversity unfolds, considering the full range of forces and processes acting on biodiversity, and lastly revisiting concepts and extending models.

Rather than commenting sequentially on each paper in this special issue, we have chosen a summary to gather the ideas and suggestions presented around these themes—all the more so as several articles contribute to multiple themes (Figure 1). They are not presented in order of importance, although some papers offer more general perspectives than others. Of course, this special issue does not exhaust the field of possibilities. Each paper suggests several avenues for further research, and we also mention (Conclusion) some additional research directions that are not considered here, but worth exploring.

The border between ecology and evolution is a vast domain, and this special issue of course did not explore it fully. Here, we sketch out a few further directions and themes that could fruitfully be pursued. First, technological tools (e.g. omics and environmental sensors/probes) used by evolutionary biologists and ecologists are serving as common objects for a dialogue between the two communities. Although they were not covered explicitly here, the idea runs through most papers of the special issue. Second, fitness is the currency used in evolutionary biology and energy that is used by the most functional parts of ecology. Rather abstract frameworks have been proposed to link fitness and energy (entropy) in evolutionary biology (e.g. Frank, 2009). The approach of Brown et al. (2018), connecting energy use, traits and environment, is open to empirical evaluation, and might be pursued for understanding EED. Third, micro-organisms represent interactive interfaces between macro-organisms and their environment, which is encapsulated in the holobiont concept (Simon et al., 2019). Both evolutionary and ecological paradigms are required to make sense of holobiont dynamics with echoes here in the contributions of Loreau et al. (2010) and Martiny et al. (2023), for example, on the notion of transmission units. Last, but not least, biodiversity management in a world of very fast and deleterious environmental changes should harness an eco-evolutionary framework and perspective (Sarrazin & Leconte, 2016), not only to manage the current problems but also to offer some hope for the future.

Both authors drafted and wrote the manuscript.

PJ has co-authored three papers in this special issue of Ecology Letters.