Density-Dependent Natal Dispersal Patterns in a Leopard Population Recovering from Over-Harvest

Abstract

Natal dispersal enables population connectivity, gene flow and metapopulation dynamics. In polygynous mammals, dispersal is typically male-biased. Classically, the ‘mate competition’, ‘resource competition’ and ‘resident fitness’ hypotheses predict density-dependent dispersal patterns, while the ‘inbreeding avoidance’ hypothesis posits density-independent dispersal. In a leopard (Panthera pardus) population recovering from over-harvest, we investigated the effect of sex, population density and prey biomass, on age of natal dispersal, distance dispersed, probability of emigration and dispersal success. Over an 11-year period, we tracked 35 subadult leopards using VHF and GPS telemetry. Subadult leopards initiated dispersal at 13.6 ± 0.4 months. Age at commencement of dispersal was positively density-dependent. Although males (11.0 ± 2.5 km) generally dispersed further than females (2.7 ± 0.4 km), some males exhibited opportunistic philopatry when the population was below capacity. All 13 females were philopatric, while 12 of 22 males emigrated. Male dispersal distance and emigration probability followed a quadratic relationship with population density, whereas female dispersal distance was inversely density-dependent. Eight of 12 known-fate females and 5 of 12 known-fate male leopards were successful in settling. Dispersal success did not vary with population density, prey biomass, and for males, neither between dispersal strategies (philopatry vs. emigration). Females formed matrilineal kin clusters, supporting the resident fitness hypothesis. Conversely, mate competition appeared the main driver for male leopard dispersal. We demonstrate that dispersal patterns changed over time, i.e. as the leopard population density increased. We conclude that conservation interventions that facilitated local demographic recovery in the study area also restored dispersal patterns disrupted by unsustainable harvesting, and that this indirectly improved connectivity among leopard populations over a larger landscape.

Population recovery highlights spatial organization dynamics in adult leopards

“…Females are more likely to tolerate each other and benefit from inclusive fitness, and should face the costs of dispersal only when the costs of resource competition in the natal range are higher (Lambin et al ., ). Female dispersal might therefore only occur under long‐lasting stability of both elevated population density, and socio‐spatial organization (Fattebert et al ., ). Spatial tactics of female leopards in Phinda were congruent with the mounting evidence that matrilines spatially structure the female segment of the population in other polygynous mammals (brown bear Ursus arctos : Støen et al ., ; tiger: Goodrich et al ., ; wild boar Sus scrofa : Podgórski, Scandura & Jędrzejewska, ).…”

“…Such partial inter‐sexual overlap is congruent with the promiscuous mating behavior of female leopards to possibly confuse paternity as a strategy to reduce the risk of infanticide (Balme & Hunter, ). Male spacing stability also paralleled elevated subadult male emigration probability, and longer dispersal distances reported elsewhere (Fattebert et al ., ).…”

“…Overall competitor populations (lions Panthera leo and spotted hyena Crocutta crocutta ) were also stable (Balme et al ., ), and the leopard demographic recovery between 2005–2008 was attributed to the decline of human‐caused mortality (Balme et al ., ). During the course of the study, all radio‐tracked subadult females remained philopatric, while emigration rate and natal dispersal distance in subadult males increased with population density (Fattebert et al ., ).…”

“…Under a dispersal‐regulated alternative to the classical dual strategy, females are predicted to relinquish part of their home range to philopatric daughters at independence, and overlap more with related females that can benefit from local knowledge of resources, and inclusive fitness (Anderson, ; Lambin, Aars & Piertney, ). In contrast, mate competition predicts density‐dependent subadult male emigration rates (Fattebert et al ., ) with stable adult male spacing.…”

Context dependency of top‐down, bottom‐up and density‐dependent influences on cheetah demography

“…Whereas cheetahs in the Serengeti sometimes move great distances to follow migratory prey (Durant, Caro, Collins, Alawi, & Fitzgibbon, ), and are able to immigrate and emigrate, the fenced boundaries of our study area resulted in little seasonal home range shifts and a lack of long‐distance dispersal. Contrary to leopards (Fattebert, Balme, Dickerson, Slotow, & Hunter, ), the inability of cheetahs to disperse out of the fenced reserve, along with high local concentrations of predators and prey, may result in the changing community‐level spatial relationships and behaviour that we hypothesize were the mechanisms behind our observed survival trends. Additionally, our study area contains areas of dense vegetation, which could reduce cheetah mortality from lions by acting as a predation refuge (Mills & Mills, ), whereas the open plains of the Serengeti do not offer substantial cover for hiding cheetahs.…”