Evolutionary conservation advice for despotic populations: habitat heterogeneity favours conflict and reduces productivity in Seychelles magpie robins

Abstract

Individual preferences for good habitat are often thought to have a beneficial stabilizing effect for populations. However, if individuals preferentially compete for better-quality territories, these may become hotspots of conflict. We show that, in an endangered species, this process decreases the productivity of favoured territories to the extent that differences in productivity between territories disappear. Unlike predictions from current demographic theory on site-dependent population regulation (ideal despotic distribution), we show that population productivity is reduced if resources are distributed unevenly in space. Competition for high-quality habitat can thus have detrimental consequences for populations even though it benefits individuals. Manipulating conflict (e.g. by reducing variation in habitat quality) can therefore prove an effective conservation measure in species with strong social or territorial conflict.

Population regulation of territorial species: both site dependence and interference mechanisms matter

“…In the Seychelles magpie robin (Copsychus sechellarum), it has been demonstrated that interference through territorial disputes increases with increasing density and has the potential to reduce fitness [13]. Similarly, interference effects owing to both territory shrinkage and territorial disputes on reproductive success were crucial for the population dynamics of the Seychelles warbler (Acrocephalus sechellensis) [15].…”

“…In a system regulated by site dependence, improving the quality of breeding sites should allow population size recovery [9,11]. In contrast, if interference mechanisms regulate population size, restoration measures should focus on improving poor habitat patches to reduce heterogeneity in habitat quality and decrease conflict pressure, as recommended for the Seychelles magpie robin [13]. Although increasing the number of sites (nest-boxes) in the best habitat patches might increase the average breeding success of the Mauritius kestrel, this study suggests that such management would have little impact on the population growth rate if not coupled with action at a larger scale to expand high-quality habitat in order to reduce interference competition among juveniles.…”

“…This is because most studies have only focused on single vital rates, particularly reproductive parameters [8][9][10][11][12][13][14][15][16][17], and have typically not explored the role of spatial mechanisms in a population-dynamics context. Survival, however, may contribute profoundly to population growth rate as it frequently outweighs the contribution of reproduction, particularly in long-lived species [18,19], and variability in juvenile survival may play an important role in population dynamics [20,21].…”

“…Here, interference does not refer to the direct physical exclusion by conspecifics, but to density-dependent competition for resources (e.g. increased aggressiveness between social group members [13] interfering with foraging, survival or reproduction; territory compression [14,15]), or adverse conditions induced by higher density (e.g. increased parasitic load [16]).…”

Biodiversity in the context of ecosystem services: the applied need for systems approaches

“…This conflict reduces the frequency of breeding on territories (figure 1b) [24]. Furthermore, subordinates are more common on the best-quality territories, increasing territorial conflict and reducing breeding success to levels associated with the poorest quality territories (figure 1c) [24,25]. Not surprisingly, territorial conflict has implications for population growth (figure 1d) [24].…”