Data for: Termites have wider thermal limits to cope with environmental conditions in savannas

The most diverse and abundant family of termites, the Termitidae, evolved
in African tropical forests. They have since colonised grassy biomes such
as savannas. These open environments have more extreme conditions than
tropical forests, notably wider extremes of temperature and lower
precipitation levels and greater temporal fluctuations (both annual and
diurnal variation). These conditions are challenging for soft-bodied
ectotherms, such as termites, to survive in, let alone become as
ecologically dominant as termites have. Here, we quantified termite
thermal limits to test the hypothesis that these physiological limits have
widened in savanna termite species to facilitate their existence in
savanna environments. We sampled termites directly from mound structures,
across an environmental gradient in Ghana, ranging from wet tropical
forest through to savanna. At each location we quantified both Critical
Thermal Maximum (CTmax) and Critical Thermal Minimum (CTmin) of all the
most abundant mound-building Termitidae species in the study areas. We
modelled the thermal limits in two separate mixed effects models against:
canopy cover at the mound, temperature and rainfall, as fixed effects,
with sampling location as a random intercept. For both CTmax and CTmin
savanna species had significantly more extreme thermal limits than forest
species. Between and within environments, areas with higher amounts of
canopy cover were significantly associated with lower CTmax values of the
termite colonies. CTmin was significantly positively correlated with
rainfall. Temperature was retained in both models, however it did not have
a significant relationship in either.  Sampling location
explained a large proportion of the residual variation, suggesting there
are other environmental factors that could influence termite thermal
limits. Our results suggest there has been a widening of the thermal
limits in termite savanna species. These physiological differences, in
conjunction with other behavioural adaptations, are likely to have enabled
termites to cope with the more extreme environmental conditions found in
savanna environments and facilitated their expansion into open tropical
environments.