Understanding Unanticipated Range Shifts: Biotic Interactions as Key Mediators in a Changing Climate

Abstract

Climate change poses one of the greatest threats to species survival in the 21st century. However, predicting species responses, identifying the most vulnerable species and locations, and determining effective conservation interventions remain significant challenges. Many studies employ correlative approaches to understand how species climate niches might be expected to shift under a changing climate by “tracking climate” and maintaining their climate niche. Species distribution models (SDMs) remain the primary tool for anticipating responses to climate change, yet most models are built on a straightforward correlation between current distribution points and prevailing environmental conditions. However, it is increasingly evident that a more nuanced, ecologically based approach is necessary (Lucas et al. 2025). In newly published research in Global Change Biology, Osmolovsky et al. (2025) investigate the longstanding proposition that species will move upslope or away from the equator under climate change, or rather, when and why this is not always the case. However, mounting evidence shows that this is frequently not the case, with over a third of species examined (20%–37%) showing “counterintuitive” responses (Rubenstein et al. 2023). This challenges the longstanding view of the need to track climatic niches and undermines the ability of models to perform accurately. Understanding why this might occur is clearly crucial for grasping the impacts of climate change, including where and why this might occur, especially given differing responses across species, even within a single locality (Gibson-Reinemer and Rahel 2015). Importantly, understanding that these responses are not merely “an exception” is crucial, not only because they represent a large proportion of all known responses, but because the mechanistic elements provide insights into how and why species respond differently.

Osmolovsky et al. highlight the potential role of biotic interactions as a mediating factor to explain these unanticipated shifts, proposing the ‘Interaction Opportunists Hypothesis’. This hypothesis highlights that counterintuitive shifts to climate change may reflect changes in biotic interactions at the warmer edge of species' distributions. Further, these changing interactions may manifest through a number of different mechanisms. Principally the study explores three forms of interaction: reduced antagonistic interactions, increased positive interactions, and changes in equilibrium due to shifts in competitive dynamics between species. Ultimately these changes would either increase the suitability of previously marginal habitats on the warmer edge of the range (i.e., increasing the abundance of key resources) or reduce pressures that previously prevented species from occupying these spaces (such as predation pressure).

The “stress trade-off hypothesis”, anticipates that the cooler edge of species ranges will be delimited by climate, whilst the warmer edge of the range will be determined by biotic interaction. As such, agonistic (negative) interactions, such as competition, or predation could potentially decrease on the warmer edge of the range, potentially as predators are more likely to be larger-bodied and therefore sensitive to climate change. In addition, warming climate may actively reverse generally antagonistic relationships to help increase the potential survival of the host under stress (as a harmful parasite or pathogen kills its host). However, only a limited number of studies have shown support for this. Furthermore, lags in responses may allow temporary persistence of a species in some of these spaces, further altering the interactions present; and further complicating patterns of response, and our ability to understand them.

Yet interpreting the drivers of range shift may be challenging. For example, most species have their realised niche truncated, either due to land-boundaries (and other physical barriers) or the loss of lower elevations of the range due to development, or other forms of use. Recovery of habitats in the lower elevations of the range can allow recolonisation of former range i.e., Himalayan plants following the cessation of grazing, or the downhill shift of the squirrel Tamiasciurus hudsonicus following the recovery of spruce forests (Morelli et al. 2025). Basic analysis could suggest a counter-intuitive range shift in these cases, yet it is important to understand that range limits may be bounded by an array of factors, rather than climate, and alleviation of other threats may enable recolonisation or range expansion. This has fundamental implications for analysing the effects of climate change on species distributions, as even if species may track climate change, models based on truncated data will over-estimate the impacts of those changes.

Additionally, other characteristics and traits of species also likely need to be considered. For example, studies have shown that in anurans, climate extremes favor medium body sizes, selecting against very large or very small species (Feijó et al. 2023), and this trend is present over temporal, spatial, and elevational gradients. For other taxa, a suite of traits has been shown to play a role in predicting responses (MacLean and Beissinger 2017). Thus, ignoring key traits, as well as biotic interactions, will likely undermine our ability to predict responses to a changing climate. Furthermore, the mean elevation of occurrence is also likely related to key traits that play significant roles in determining species' responses (Mamantov et al. 2021), though it should be noted that how traits may interact and their contribution in determining species range shifts remains an area that requires further work. Other important dimensions that need to be considered are changes in precipitation (which may not follow the same patterns as temperature) as well as changes in climate extremes and extreme events, which may lead to changes in distributional changes that do not correlate with mean changes in temperature (Latimer and Zuckerberg 2019).

This myriad of different responses across space, time, and taxa highlights a number of key points. Firstly, simple correlative models are insufficient for understanding the impacts of climate change, highlighting the urgent need to re-examine our approaches to predicting the impact of climate change and, especially, to avoid over-reliance on models. Secondly, this reminds us of the need to better reflect species ecology in models, for example, better reproducing non-linear responses to changing climates and how the impacts manifest differently depending on when these changes occur (based on lifecycle) as well as how climate extremes impact distribution. Building on this, while experiments may be needed to better model thermal niches and changes in tolerance—especially in novel climates (Kearney and Porter 2020)—further work will be necessary to translate these findings into natural environments, considering species interactions (Osmolovsky et al. 2025). This is likely especially true in montane ecosystems. Furthermore, it should be noted that when climate change occurs and how it impacts other elements of the ecosystem (e.g., species phenology) has the potential to cause trophic cascades due to reliance on different cues to trigger phenological events, causing mismatches. How these interactions and shifts manifest on climate gradients is particularly complex, and more work will be needed to understand these interactions and their sensitivity to change.

Further work is clearly needed to build on these theories, and better understand how species interactions contribute to species' abilities not only to potentially withstand a changing climate, but also to potentially expand their ranges. Until we better understand what is limiting species ranges, and how species interactions play a part in this, predicting species future responses to changes in climate will likely continue to have high rates of error. Better understanding the role of biotic interactions is critical for improving forecasts of species' responses and vulnerabilities to changing climates, and thus apportioning resources to best meet species needs. The framework provided by Osmolovsky et al. (2025) is a solid step toward untangling yet another piece of the complex puzzle of understanding and predicting how species may respond to a changing climate, further refining our ability to understand, predict, and conserve species in a changing world.

Muyang Wang: conceptualization, funding acquisition, project administration, supervision, writing – original draft, writing – review and editing. Yingying Zhuo: writing – original draft. Alice C. Hughes: writing – original draft, writing – review and editing. Weikang Yang: funding acquisition, writing – review and editing.

The authors declare no conflicts of interest.

This article is a Invited Commentary on Inna Osmolovsky et al. https://doi.org/10.1111/gcb.70332.