Life history benefits of residency in a partially migrating pond‐breeding amphibian

Abstract

Species with partial migration, where a portion of a population migrates and the other remains residential, provide the opportunity to evaluate conditions for migration and test mechanisms influencing migratory decisions. We conducted a five-year study of two populations of red-spotted newts (Notophthalmus viridescens), composed of individuals that either remain as residents in the breeding pond over the winter or migrate to the terrestrial habitat. We used multistate mark-recapture methods to (1) test for differences in survival probability between migrants and residents, (2) determine if migrants breed every year or skip opportunities for reproduction, and (3) estimate the frequency of individuals switching migratory tactic. We used estimates of life history parameters from the natural populations in combination with previous experimental work to evaluate processes maintaining partial migration at the population level and to assess mechanisms influencing the decision to migrate. Based on capture-recapture information on over 3000 individuals, we found that newts can switch migratory tactics over their lifetime. We conclude that migrants and residents coexist through conditional asymmetries, with residents having higher fitness and inferior individuals adopting the migrant tactic. We found that newts are more likely to switch from residency to migrating than the reverse and males were more likely to remain as residents. Migration differences between the sexes are likely driven by reproduction benefits of residency for males and high energetic costs of breeding resulting in lower breeding frequencies for females. Environmental conditions also influence partial migration within a population; we found support for density-dependent processes in the pond strongly influencing the probability of migrating. Our work illustrates how migration can be influenced by a complex range of individual and environmental factors and enhances our understanding of the conditions necessary for the evolution and maintenance of partial migration within populations.

Potential Effects of Changes in Temperature and Food Resources on Life History Trajectories of Juvenile Oncorhynchus mykiss

“…Results of model simulations identifying the proportion of female O. mykiss that will adopt an anadromous life history trajectory (i.e., become Steelhead smolts) under different climate scenarios and prey availability (see Table 2 for values that correspond to changes in prey availability). Grayson et al 2011). In Steelhead, marine survival has been observed to increase with body size (Ward and Slaney 1988) and age of smolts (Holtby 1988).…”

The ‘male escape hypothesis’: sex-biased metamorphosis in response to climatic drivers in a facultatively paedomorphic amphibian

“…Females may need to stay in water longer than males to fuel up their reserves after they have laid eggs during breeding [65]. In contrast to studies in permanent ponds, where it can be favourable for males to stay in water to get earlier access to females at the next breeding season [62], males living in temporary ponds do not have competitive sexual advantages to remain in water.…”

“…Second, looking more broadly into sex-biased dispersal, there are variations in the propensity of males or females to be the most dispersing or philopatric sex. For instance, in red-spotted newts, males are more resident than females in overwintering in ponds, whereas females move to land [62]. Similarly, in tiger salamanders, paedomorphic males are more philopatric than females to their ponds.…”

Home on the Range: Factors Explaining Partial Migration of African Buffalo in a Tropical Environment

“…Alternatively, animals within a population may show conditional migratory behaviour that depends on variation in individual (age, sex, behaviour), social (conspecific densities, position in dominance hierarchy), or environmental (predation risk, availability of resources such as food and breeding sites) factors [3]. Partial migration has been documented in a variety of taxa, including mammals [3], [4], [5], fish [6], birds [7], and amphibians [8].…”