Férnandez-Chacón, A., Genovart, M., Álvares, D.,Cano, J.M, Ojanguren, A.F., Rodriguez-Muñoz, R.,Nicieza, A.G. Neighbouring populations, opposite dyanmics: influence of body size and environmental variation on the demography of stream-resident brown trout (Salmo trutta). Oecologia
In organisms such as fish, where body size is considered an important
state variable for the study of their population dynamics, size-specific
growth and survival rates can be influenced by local variation in both
biotic and abiotic factors, but few studies have evaluated the complex
relationships between environmental variability and size-dependent
processes. We analysed a 6-year capture–recapture dataset of brown trout
(Salmo trutta) collected at 3 neighbouring
but heterogeneous mountain streams in northern Spain with the aim of
investigating the factors shaping the dynamics of local populations. 
The
influence of body size and water temperature on survival and individual
growth was assessed under a multi-state modelling framework, an
extension of classical capture–recapture models that considers the state
(i.e. body size) of the individual in each capture occasion and allows
us to obtain state-specific demographic rates and link them to
continuous environmental variables. Individual survival and growth
patterns varied over space and time, and evidence of size-dependent
survival was found in all but the smallest stream. At this stream, the
probability of reaching larger sizes was lower compared to the other
wider and deeper streams. Water temperature variables performed better
in the modelling of the highest-altitude population, explaining over a
99 % of the variability in maturation transitions and survival of large
fish. The relationships between body size, temperature and fitness
components found in this study highlight the utility of multi-state
approaches to investigate small-scale demographic processes in
heterogeneous environments, and to provide reliable ecological knowledge
for management purposes.
The
influence of body size and water temperature on survival and individual
growth was assessed under a multi-state modelling framework, an
extension of classical capture–recapture models that considers the state
(i.e. body size) of the individual in each capture occasion and allows
us to obtain state-specific demographic rates and link them to
continuous environmental variables. Individual survival and growth
patterns varied over space and time, and evidence of size-dependent
survival was found in all but the smallest stream. At this stream, the
probability of reaching larger sizes was lower compared to the other
wider and deeper streams. Water temperature variables performed better
in the modelling of the highest-altitude population, explaining over a
99 % of the variability in maturation transitions and survival of large
fish. The relationships between body size, temperature and fitness
components found in this study highlight the utility of multi-state
approaches to investigate small-scale demographic processes in
heterogeneous environments, and to provide reliable ecological knowledge
for management purposes. 
