Age-specific survival of territorial and nonterritorial male chamois

How alternative reproductive tactics (ARTs) are maintained in wildlife
populations is one of the major questions in evolutionary biology. As a
dominant status, territoriality is typically linked to increased mating
opportunities, and one explanation for why this behaviour coexists with
other tactics is that dominance implies survival costs. Such a trade-off
may occur in the Northern chamois Rupicapra rupicapra, as
reproductive advantages of territorial males over nonterritorial males
could be counterbalanced by a reduction in survival mediated through
energy expenditure, stress and parasitic infections, ultimately favouring
ART coexistence. Here, we analysed age-dependent survival probabilities of
territorial (n=15) and nonterritorial (n=16) adult chamois using
information collected over 12 years between 2010 and 2021 in the Gran
Paradiso National Park (Western Italian Alps). Survival rates were
estimated with a CMR approach using Burnham’s joint modelling of live
encounter and dead recovery data. The model selection procedure, based on
AICc value minimisation, supported a linear decrease of survival with age
but did not match our predictions, as territorial chamois did not have
lower survival rates than nonterritorial chamois. In contrast, territorial
males appeared to enjoy reproductive success at lower survival costs.
This, in turn, supports the role of other factors, such as snow-dependent
environmental stochasticity, in the maintenance of ARTs in chamois
populations. The limited sample size, however, calls for caution in
interpretation, and long-term studies of lifetime reproductive success and
survival are necessary to clarify the mechanisms underlying the expression
and coexistence of different reproductive behaviours in this species.