The multidimensional (and contrasting) effects of environmental warming on a group of montane tropical lizards: Lizard and plant data

1. Mountains are cradles for biodiversity and crucibles for climate-driven
species loss, particularly for tropical ectotherms. Constriction on
activity and amplified heat stress are two key sources of warming-driven
vulnerability in tropical montane ectotherms. These threats, however,
might be counterbalanced if rising temperatures also release organisms
from limits on activity induced by cold stress. 2. We used biophysical
modeling to estimate activity patterns and thermal stress under warming in
a group of summit-dwelling Anolis lizards (A. armouri and A. shrevei)
endemic to the Caribbean island of Hispaniola. Activity is currently
constrained by the prevalence of temperatures too cold for activity. Under
warming, our models predict expanded hours of potential activity and
reduced cold stress, especially under a high emission scenario. Crucially,
release from cold stress does not come at the expense of heightened
exposure to heat stress. This result arises from a steep mismatch between
these species’ warm-adapted ecology and the surprisingly cold environments
they occupy. 3. Yet, resilience in some dimensions belies vulnerability
along others, particularly with regards to critical macrohabitat. We
capitalized on a long-term monitoring dataset to predict forest
distributions under warming. Our models predict upslope shifts in montane
cloud forests that may constrict the high-elevation pine forests to which
these lizards are inexorably linked. Warming-driven macrohabitat loss can
‘pin’ the montane endemics into progressively shrinking ranges, especially
since a rising cloud forest also facilitates upslope transport of a close
relative, A. cybotes (a species associated with broadleaf forests). 4.
Many tropical ectotherms (including these anoles) are adapted to forest
edges, a feature often associated with a relatively warm-adapted
ecophysiology. When such species are also found in cool environments, such
as those found on mountaintops, warming-amplified thermal stress is
surprisingly limited. Therefore, the direct effects of warming on tropical
ectotherms are quite broad, and can even include potential benefits to
fitness-based activities. 5. Rising temperatures may often present a
dual-edged sword: warming simultaneously releases these organisms from
constraints on activity while exposing them to other threats. Whether due
to the direct or indirect effects of climate warming, exceptional
vulnerability may indeed reside where biodiversity is highest.