Intermediate habitat fragmentation buffers droughts: How individual energy dynamics mediate mammal community response to stressors

Biodiversity is threatened by land-use and climate change. Although these
processes are known to influence species survival and diversity,
predicting their combined effects on communities remains challenging. We
here aim to disentangle the combined effects of drought-induced resource
shortage and habitat fragmentation on species coexistence. To understand
how both fragmentation and droughts affect individual movement and
physiology, and ultimately influence population and community dynamics, we
use an individual-based metabolic modelling approach to simulate a
community of small mammals. Individuals forage in the landscape to ingest
energy, which they then allocate to basal maintenance, digestion,
locomotion, growth, reproduction, and storage. If individuals of several
species are able to balance their energy intake and needs, and
additionally store energy as fat reserve, they may overcome stress periods
and coexist. We find that species recover best after a drought when they
live in moderately fragmented landscapes compared to those with low or
high fragmentation. In low fragmented landscapes, high local competition
during resource shortages is problematic, while in highly fragmented
landscapes, low energy balance and storage often lead to high mortality
during drought. Intermediately fragmented landscapes balance these effects
and show the least impact of droughts on species richness, a pattern that
holds also when integrating observed drought time series from monitoring
data in the model simulations. Due to the interacting negative impacts, we
suggest that with ongoing global change, it is increasingly important to
understand stressors simultaneously to identify measures that support
species coexistence and biodiversity. Including individual energy dynamics
allowed us to conflate the different global change effects through energy
storage and energy allocation to different processes. Our presented
community model, which integrates metabolic and behavioural reactions of
individuals to different stressors and scales them to the community level,
offers valuable insights with great potential to support nature
conservation.