Critical transitions and evolutionary hysteresis in movement: Habitat fragmentation can cause abrupt shifts in dispersal that are difficult to revert

Under habitat fragmentation, plant species’ survival hinges on the ability
of individuals to disperse from one habitat patch to another. While there
is evidence that severe habitat fragmentation leads to evolution of
reduced dispersal ability and that such decreased mobility is generally
detrimental for species’ survival, it is unknown whether species adapt via
a gradual loss in dispersal ability or via a sudden shift from frequent to
infrequent dispersal between patches (i.e., a critical transition). Using
both a spatially explicit deterministic and individual-based stochastic
model of hydrochorous seed dispersal, we show that a small increase in
inter-patch distance can generate an abrupt shift in plant seed dispersal
strategy from long to short distances. Most importantly, we found that a
substantial increase in connectivity between habitat fragments is required
to reverse this loss of long-distance dispersal, due to an evolutionary
hysteresis effect. Our theory prompts for re-consideration of the
eco-evolutionary consequences of habitat fragmentation as restoring
habitat connectivity may require restoration of much higher connectivity
levels than currently assumed.