Incorporating spatial structure and stochasticity in endangered Bonelli’s eagle’s population models: Implications for conservation and management

Abstract

A B S T R A C TPopulation models have played a chief role informing management decisions for the endangered Bonelli's eagle (Aquila fasciata) in Spain. In this paper, we incorporate spatial structure and stochasticity in the construction of individual-based metapopulation models, and use these models to explore the effects of possible management actions on the persistence of the species in Spain. To build the models we used data on seven subpopulations that have experienced different trends in the last decades, and we introduced new estimates of pre-adult survival rate. The elasticity analysis of our models showed that when the interchange of individuals among sub-populations is taken into account, preadult mortality plays the key role in determining the overall population trend. This is in contrast to what it has been suggested by previous demographic models that modelled local populations as isolated. Specifically, a 20% decrease in pre-adult mortality during the first two years of life was enough for the stabilization of the metapopulation (i.e., k P 1.0). However, neither a similar decrease in the values of adult mortality, nor an increase in the percentage of breeders, modified the declining trend of our model metapopulation. This reinforces the idea that to ensure the long-term persistence of the species in Spain, management actions should aim at minimizing pre-adult mortality. These include locating and protecting the areas used by juvenile Bonelli's eagles (e.g., temporary settlements), minimizing the risk of electrocution in power lines, and preventing human persecution. Introduction 53During the last decades there has been an increasing aware-54 ness of the roles of space and environmental and demo-55 graphic stochasticity in populations' dynamics (e.g., Tilman 56and Kareiva, 1997;Hanski, 1999;Lande et al., 2003), with com-57 puter simulations playing a key role in the analysis of the ef-58 fects of those factors on populations' trajectories 59 (Lindenmayer et al., 1995;Hanski, 1999). For stage-structured 60 populations an alternative to simulations for projecting pop-61 ulation trajectories is the use of matrix population models 62 (e.g., Caswell, 2001). These matrix population models have 63 been influential in the derivation of management recommen-64 dations for many endangered species (e.g., Crouse et al., 1987; 0006-3207/$ -see front matter Ó 2008 Published by Elsevier Ltd. doi:10.1016/j.biocon.2008.01.011 * Corresponding author: Address: Estació n Bioló gica Terra Natura, CIBIO -Fundació n Terra Natura, Universidad de Alicante, Apdo. 99 E, 03080 Alicante, Spain. Tel.: +34 965903400x3202; fax: +34 963543670. Q2E-mail addresses: Pascual.Lopez@uv.es, lopez.pascual@gmail.com (P. Ló pez-Ló pez). and use these models to explore the effects of possible man-107 agement actions on the persistence of the species in Spain.a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c 108 Methods 109We used the Vortex simulations software (Lacy, 1993(Lacy, , 2000 110 Lacy et al., 2005) to develop model...

Markov models of territory occupancy: implications for the management and conservation of competing species

“…increasing juvenile survival) are needed, whereas strategies based solely on decreasing adult mortality and territory abandonment (such as decreasing perturbations to Bonelli's eagle territories or increasing prey availability) are unlikely to suYce. This also agrees with the Wndings of Soutullo et al (2008) based on demographic models. Given Bonelli's eagles large dispersal distances (Cadahía et al 2005(Cadahía et al , 2006, decreasing the mortality of dispersing individuals requires a large-scale regional management framework.…”

“…On the other hand, improving power line design will decrease both juvenile and adult mortality. Both strategies are needed and should be enforced, yet, our results (and those of Soutullo et al 2008) suggest that without action aimed at increasing juveniles survival and the colonization of new territories, population declines are likely.…”

“…Ferrer and Hiraldo 1992;Ontiveros et al 2004;López-López et al 2007a, b). Actually, enhancing juvenile survival has been recently demonstrated as a key factor to maintain the Bonelli's eagle population in Spain, given current conditions (Soutullo et al 2008).…”

“…These include decreasing perturbations (e.g. direct persecution) in the areas that are abandoned or remain vacant (Carrete et al 2002a(Carrete et al , b, 2005(Carrete et al , 2006, controlling golden eagles populations (Carrete et al 2002a, b), enhancing nesting site suitability for breeding, including increasing food supply (Carrete et al 2002a, b;Gil-Sánchez et al 2004;Ontiveros et al 2004Ontiveros et al , 2005, reducing adult mortality (Carrete et al 2002a, b;Gil-Sánchez et al 2004), and decreasing the mortality of dispersing individuals (Ontiveros and Pleguezuelos 2000;Carrete et al 2002aCarrete et al , 2005Soutullo et al 2008). These measures can be grouped into two main management strategies: (a) those aimed at decreasing juvenile mortality, and thus encouraging Bonelli's eagle colonization of new territories, and (b) those aimed at decreasing adult mortality and the abandonment of occupied territories.…”

Linking density, productivity and trends of an endangered species: The Bonelli's eagle in Spain

“…We found a positive relationship between productivity, density and recent population trend, which suggests that the Spanish population of Bonelli's eagle show a very large spatial heterogeneity in these three demographic parameters, and that it may be suffering from a high mortality or low productivity that maintain it below carrying capacity. High mortality of the breeding segment of the population has been observed (Real et al 2001) and, as a consequence, juvenile floater individuals find and occupy vacant territories, or mate with owners of territories after the disappearance of one of the members of a breeding pair (see Balbontín et al 2003, Penteriani et al 2006, and Soutullo et al 2008 for longlived Mediterranean raptors). This reduction in age at first breeding and productivity has been proposed as a consequence of unnatural events caused by human persecution in the Bonelli's eagle .…”