Thermoregulatory traits combine with range shifts to alter the future of montane ant assemblages

Abstract

Predicting and understanding the biological response to future climate change is a pressing challenge for humanity. In the 21st century, many species will move into higher latitudes and higher elevations as the climate warms. In addition, the relative abundances of species within local assemblages are likely to change. Both effects have implications for how ecosystems function. Few biodiversity forecasts, however, take account of both shifting ranges and changing abundances. We provide a novel analysis predicting the potential changes to assemblage-level relative abundances in the 21st century. We use an established relationship linking ant abundance and their colour and size traits to temperature and UV-B to predict future abundance changes.We also predict future temperature driven range shifts and use these to alter the available species pool for our trait-mediated abundance predictions. We do this across three continents under a low greenhouse gas emissions scenario (RCP2.6) and a business-as-usual scenario (RCP8.5). Under RCP2.6, predicted changes to ant assemblages by 2100 are moderate. On average, species richness will increase by 26%, | 2163 BISHOP et al.

Repeated surveying over 6 years reveals that fine-scale habitat variables are key to tropical mountain ant assemblage composition and functional diversity

“…The implications of our findings are that studies focused on large scale measures like altitude may risk missing fine-scale changes associated with heterogeneous habitats. Habitat structure buffers changes in temperature and models based on temperature alone could overestimate the impact of climate change 65,66 . Fine-scale data collection is often laborious and costly, yet these data may make valuable contributions to large-scale models that would otherwise overlook microclimatic effects 23 .…”

“…Here, we find that FD is well explained by finer-scale measures of habitat. That FD, and to some extent species composition, are influenced by fine-scale factors implies that predicting species' responses to climate change is complicated by habitat structure and may not be well predicted by only broad-scale predictors such as temperature and elevation 66 . This has implications for management: if vegetation structure can be maintained and managed, ectothermic species may be less impacted than expected, and it may be possible to ameliorate some of the inexorable effects of climate change, with careful conservation strategies.…”

The impact of secondary forest regeneration on ground-dwelling ant communities in the Tropical Andes

“…As ants are ectothermic with relatively small body sizes, they are highly sensitive to temperature fluctuations, particularly surface-active species (Staab et al 2014; Araújo and Fernandes 2003). This is of particular importance to ants in the Andes, where global warming may require species to move to track narrow elevational distributions (Longino and Colwell 2011; Staab et al 2014) and where simulations under RCP8.5 predict almost a tripling of ant species richness at higher elevations underpinned by dramatic changes in the abundance distribution of species, such that currently common species become very rare (Bishop et al 2019). While we are unaware of studies documenting elevational movements in tropical ants as a result of climate change, highlighting a key knowledge gap, the average altitudes of 102 montane moth species in Borneo increased by 67 m between 1965 and 2007, with the 20 endemic species moving uphill by an average of 92 m (Chen et al 2009).…”

Reported climate change impacts on cloud forest ants are driven by sampling bias: A critical evaluation of Warne et al. (2020)

“…Ants are a commonly used indicator taxon for monitoring changes along temperature gradients (Lach et al, 2010), which makes them suitable for studying climate‐related community shifts. However, relatively little work has been conducted on ant assemblages in tropical cloud forest (e.g Mottl et al, 2019; Smith et al, 2014) despite predictions that highland assemblages are likely to change the most (Bishop et al, 2019). While the effects of habitat disturbance on ants have been well documented (Andersen, 2019), long‐term data to test for climate change effects on ants are scarce.…”

“…Most studies on the interaction of climatic changes with elevation, and the consequent species range shifts, have focused on vertebrates, plants, and moths (e.g., Cheng et al, 2019, and review there). Hence, the effects of climate change on ants are limited to modeled predictions (e.g., Bishop et al, 2019), or small‐scale experiments in temperate forests (e.g., Diamond et al, 2016). To our knowledge, only one study has monitored long‐term changes in a rain forest ant community, via multiple resurveys over a decade at 850 m a.s.l.…”