Connectivity among thermal habitats buffers the effects of warm climate on life-history traits and population dynamics

1. Contemporary climate change affects population dynamics, but its
influence varies with landscape structure. It is still unclear whether
landscape fragmentation buffers or enhances the effects of climate on
population size and on the age and body size of individuals composing
these populations. 2. This study aims to investigate the impacts of warm
climates on lizard life-history traits and population dynamics in habitats
varying in their connectivity. 3. We monitored common lizard (Zootoca
vivipara) populations for three years in an experimental system in which
both climatic conditions and connectivity among habitats were
simultaneously manipulated. We considered two climatic treatments (i.e.,
present-day climate and warm climate (+1.4°C than present-day climate))
and two connectivity treatments (i.e., a connected treatment in which
individuals could move from one climate to the other and an isolated
treatment in which movement between climates was not possible). We
monitored survival, reproduction, growth, dispersal, age and body size of
each individual in the system as well as population density through time.
4. We found that the influence of warm climates on the life-history traits
and population dynamics depended on the connectivity among thermal
habitats. Populations in warm climates were i) composed of younger
individuals only when isolated; ii) larger in population size only in
connected habitats; and iii) composed of larger age-specific individuals
independently of the landscape configuration. The connectivity among
habitats altered population responses to climate warming likely through
asymmetries in the flow and phenotype of dispersers between thermal
habitats. 5. Our results demonstrate that landscape fragmentation can
drastically change the dynamics and persistence of populations facing
climate change.