Both habitat change and local lek structure influence patterns of spatial loss and recovery in a black grouse population

The final publication is available at Springer via http://dx.doi.org/10.1007/s10144-015-0484-3Land use change is a major driver of declines in wildlife populations. Where human economic or recreational interests and wildlife share landscapes this problem is exacerbated. Changes in UK black grouse Tetrao tetrix populations are thought to have been strongly influenced by upland land use change. In a long-studied population within Perthshire, lek persistence is positively correlated with lek size, and remaining leks clustered most strongly within the landscape when the population is lowest, suggesting that there may be a demographic and/or spatial context to the reaction of the population to habitat changes. Hierarchical cluster analysis of lek locations revealed that patterns of lek occupancy when the population was declining were different to those during the later recovery period. Response curves from lek-habitat models developed using MaxEnt for periods with a declining population, low population, and recovering population were consistent across years for most habitat measures. We found evidence linking lek persistence with habitat quality changes and more leks which appeared between 1994 and 2008 were in improving habitat than those which disappeared during the same period. Generalised additive models (GAMs) identified changes in woodland and starting lek size as being important indicators of lek survival between declining and low/recovery periods. There may also have been a role for local densities in explaining recovery since the population low point. Persistence of black grouse leks was influenced by habitat, but changes in this alone did not fully account for black grouse declines. Even when surrounded by good quality habitat, leks can be susceptible to extirpation due to isolation

Predation in bird populations

International audienceOne of the classic ecological questions is how predators affect population size. This is often assessed by measuring how many individuals are killed by a predator, yet such direct effects may only be a relatively minor part of population dynamics. Predators frequently affect prey populations indirectly, with the fear of predation resulting in costly behavioural compensation that has the potential to lead to large population and community effects. Large observable lethal effects may then just represent the most easily observed "special" cases of the effects of predation on populations, with the costs of non-lethal effects being ubiquitous and usually dominant. This review explores these two ideas: that both cases where there are no population effects due to predation and those where lethal effects dominate are unusual and involve special circumstances. First, systems in which predation effects appear not to arise include (1) complete avoidance of predators by prey; (2) when other environmental factors limit populations so that predation is not additive to mortality; (3) when there are other more vulnerable prey for a predator; (4) when predators interact; (5) because the relationship of perceived predation risk with predator abundance is usually a non-linear function; (6) for the simple reason that non-lethal effects have not been considered. Second, lethal effects tend to dominate over non-lethal effects when (1) there is a high cost of compensating for predation risk associated with either a resource constraint or a particularly vulnerable niche or life-history stage (e.g. the nest stage generally for birds); (2) prey are the most popular prey of a predator or linear trophic chains operate; (3) there is evolutionary lag, such as introduced predators and naïve prey populations; (4) there are several predator species hunting the same prey in diverse ways. The presence of predators may or may not affect the of a bird population at any particular life-history stage, although in most cases it will do so through non-lethal effects and, occasionally, through lethal effects. However, the presence of predators will always affect intra- and interspecific competition and so will always affect population dynamics. Studies that wish to fully demonstrate that predation has no effect on bird populations must show that lethal effects and the costs of non-lethal compensation by the prey do not significantly change its density and, consequently, the level of competition