Influence of harvesting pressure on demographic tactics: implications for wildlife management

Abstract

Summary1. Demographic tactics within animal populations are shaped by selective pressures. Exploitation exerts additional pressures so that differing demographic tactics might be expected among populations with differences in levels of exploitation. Yet little has been done so far to assess the possible consequences of exploitation on the demographic tactics of mammals, even though such information could influence the choice of effective management strategies. 2. Compared with similar-sized ungulate species, wild boar Sus scrofa has high reproductive capabilities, which complicates population management. Using a perturbation analysis, we investigated how population growth rates (k) and critical life-history stages differed between two wild boar populations monitored for several years, one of which was heavily harvested and the other lightly harvested. 3. Asymptotic k was 1AE242 in the lightly hunted population and 1AE115 in the heavily hunted population, while the ratio between the elasticity of adult survival and juvenile survival was 2AE63 and 1AE27, respectively. A comparative analysis including 21 other ungulate species showed that the elasticity ratio in the heavily hunted population was the lowest ever observed. 4. Compared with expected generation times of similar-sized ungulates (more than 6 years), wild boar has a fast life-history speed, especially when facing high hunting pressure. This is well illustrated by our results, where generation times were 3AE6 years in the lightly hunted population and only 2AE3 years in the heavily hunted population. High human-induced mortality combined with non-limiting food resources accounted for the accelerated life history of the hunted population because of earlier reproduction. 5. Synthesis and applications. For wild boar, we show that when a population is facing a high hunting pressure, increasing the mortality in only one age-class (e.g. adults or juveniles) may not allow managers to limit population growth. We suggest that simulations of management strategies based on context-specific demographic models are useful for selecting interventions for population control. This type of approach allows the assessment of population response to exploitation by considering a range of plausible scenarios, improving the chance of selecting appropriate management actions.

Seabirds and climate: knowledge, pitfalls, and opportunities

“…I can hypothesize that changes in recruitment rates, breeding propensity and increased fertility, as well as the role of immigration in source-sink systems at local population level, all have the potential to offset potential declines in survival for example, in relation to climate change. Some of these compensatory mechanisms have been already found in harvested populations of fish and ungulates (Lebreton, 2005;Servanty et al, 2011).…”

Variation in vital‐rate sensitivity between populations of Texas horned lizards

“…Studies of latitudinal variation in adult survival among lizards and snakes were consistent with our findings. Overwinter survival in side-blotched lizards (Uta stansburiana) increased with latitude across a 15°gradient (Wilson and Cooke 2004), and survival rates of adult : 2003-20052006-20082009-2011 eastern massasaugas (Sistrurus catenatus) increased along a southwestern to northeastern cline (Jones et al 2012). Conversely, survival of black ratsnakes (Elaphe obsoleta) was higher at mid-latitudes (Sperry et al 2010).…”

“…However, such variation leads to associated differences in the elasticity patterns of those rates (Oli and Dobson 2003), with concomitant differences in their relative importance to the population growth rate. The result is that conspecific or congeneric populations may have different demographic responses to environmental perturbations and stressors, such as climate change (e.g., Lagopus sp., Sandercock et al 2005;Wilson and Martin 2012) or harvest management (Servanty et al 2011;Devenish-Nelson et al 2013). Intraspecific variation in vital rates also has led to recent conclusions that effective management or conservation may require population-or situation-specific strategies (Johnson et al 2010;Servanty et al 2011;Devenish-Nelson et al 2013).…”

“…The result is that conspecific or congeneric populations may have different demographic responses to environmental perturbations and stressors, such as climate change (e.g., Lagopus sp., Sandercock et al 2005;Wilson and Martin 2012) or harvest management (Servanty et al 2011;Devenish-Nelson et al 2013). Intraspecific variation in vital rates also has led to recent conclusions that effective management or conservation may require population-or situation-specific strategies (Johnson et al 2010;Servanty et al 2011;Devenish-Nelson et al 2013). For example, Johnson et al (2010) found that the relative importance of individual vital rates in affecting population growth differed among populations of endangered Ovis canadensis sierra, depending on the magnitude of those vital rates and the population trajectory.…”

Fluctuating food resources influence developmental plasticity in wild boar

“…Juveniles usually do not reproduce in wild boar and did here in response to the high hunting pressure [14,18]. Having reached only 33 -41% of their full body mass [14], juvenile females have to allocate a large amount of energy to both growth and reproduction.…”