Modelling the effects of sanitary policies on European vulture conservation

Abstract

Biodiversity losses are increasing as a consequence of negative anthropogenic effects on ecosystem dynamics. However, the magnitude and complexity of these effects may still be greatly underestimated. Most Old World vultures have experienced rapid population declines in recent years. In Europe, their immediate conservation depends on changes in health regulations affecting the availability of food provided by domestic carcasses. Information is lacking on the effects of a hypothetical food shortage on the population dynamics of vultures, and is necessary to assess the potential impacts of policy decisions on future changes in biodiversity and ecosystem services. A novel computational model (P-systems) was used to model these effects, forecasting a rapid decline in the Eurasian griffon vulture (Gyps fulvus). By contrast, vulture species with greater plasticity in their dietary range appeared less sensitive to declining food availability. This study extends our understanding of vulture ecosystem services, which have social and economic implications.

Figure 1. Spatial and temporal estimate of the difference between the biomass estimated by the model and the energetic requirements for the current avian scavenger population standardized by surface unit (expressed in calories per km²) in the ecosystem, for each of 10 municipalities in Catalonia, Northern Spain, according to the four scenarios of food availability considered (100%, 50%, 25% and 0% of food provided by domestic ungulates).

Figure 2. Predicted population trends for the four avian scavengers in the study area, for each of the four scenarios tested, expressed as the percentage of domestic ungulate carcasses available in the ecosystem.

Note the different y-axis scales.

Figure 3

(a) Possible avian scavenger foraging movements between areas, when there is a lack ofresources.The continuous lines are the possible movements of the bearded vulture (Gypaetus barbatus), Egyptian vulture (Neophron percnopterus), and cinereous vulture (Aegypius monachus). The dashed line represents the Eurasian griffon vulture (Gyps fulvus). (b) Distribution of the ten areas considered in the study: VA: Val d'Aran; AR:Alta Ribagorça; PJ: Pallars Jussà; PS: Pallars Sobirà; AU: Alt Urgell; C: Cerdanya; R: Ripollès; B: Berguedà; S: Solsonès; N: Noguera. A, F, and PPO correspond to peripheral areas (alternative environments in the model) in which the population might obtain alternative food resources outside of the study area (see more details in Methods).

Figure 4. Predicted population trend of the Eurasian griffon vulture in the different areas, according the four scenarios of domestic carcasses available.

The population increase in several areas in which the species is initially absent (VA and C) or of low densities is a consequence of spatial changes related with food shortages or maximum carrying capacity.

Figure 5. Scheme of the model.

The model takes into account two periods (summer and winter) and the basic processes of reproduction, mortality, and feeding. The scavenger birds forage in others areas when insufficient resources are available (i.e., they move). If food is scarce, the animals take the food and return to their initial area. They change territory if space is scarce. The carrying capacity of each area is limited and it is necessary to control the number of animals present. Before repeating the loop, it is necessary to restore the initial configuration. Two executions of a loop are equivalent to the passage of one year in the ecosystem.