Decline and recovery of a large carnivore: environmental change and long-term trends in an endangered brown bear population

Abstract

Understanding what factors drive fluctuations in the abundance of endangered species is a difficult ecological problem but a major requirement to attain effective management and conservation success. The ecological traits of large mammals make this task even more complicated, calling for integrative approaches. We develop a framework combining individual-based modelling and statistical inference to assess alternative hypotheses on brown bear dynamics in the Cantabrian range (Iberian Peninsula). Models including the effect of environmental factors on mortality rates were able to reproduce three decades of variation in the number of females with cubs of the year (Fcoy), including the decline that put the population close to extinction in the mid-nineties, and the following increase in brown bear numbers. This external effect prevailed over density-dependent mechanisms (sexually selected infanticide and female reproductive suppression), with a major impact of climate driven changes in resource availability and a secondary role of changes in human pressure. Predicted changes in population structure revealed a nonlinear relationship between total abundance and the number of Fcoy, highlighting the risk of simple projections based on indirect abundance indices. This study demonstrates the advantages of integrative, mechanistic approaches and provides a widely applicable framework to improve our understanding of wildlife dynamics.

Demographic projections of the Apennine brown bear population Ursus arctos marsicanus (Mammalia: Ursidae) under alternative management scenarios

“…Compared to similar applications on small bear populations (e.g. Wiegand et al 1998;Chapron et al 2003;Martínez Cano et al 2016), the strength of our findings is that all the main model's parameters have been formally estimated in recent years. The use of both a deterministic and a stochastic population projection model produced complementary information regarding the expected trend and the persistence Table III.…”

Can landscape characteristics help explain the different trends of Cantabrian brown bear subpopulations?

“…Mean litter size is 1.8 ± 0.2 cubs (n = 596 cubs) in the west and 1.3 ± 0.6 cubs (n = 99 cubs) in the east, with the former being significantly larger than the latter (Mann-Whitney test Z = -4.66, P = 0.0001, n = 29, 27) (Penteriani et al 2018). Thus, despite the consistent positive trend in population size of the western subpopulation of Cantabrian brown bears, the eastern subpopulation has had a substantially smaller population increase (Martínez Cano et al 2016). Such trends have characterised these two populations over the last forty years (Palomero et al 2007; FAPAS/FIEP 2017).…”

Canine adenovirus type 1 (CAdV-1) in free-ranging European brown bear (Ursus arctos arctos ): A threat for Cantabrian population?

“…This could also occur in those reintroduced species in areas where they had been extinct (Heard et al., ; Pedersen, Jones, Nunn, & Altizer, ; Smith, Behrens, & Sax, ). The isolation of the Cantabrian brown bear from the rest of European brown bear population for at least 400 years (Nores & Naves, ), lead to its serious population decline during the late 1990s and the division in two genetically separated (western and eastern) populations (Martínez‐Cano et al., ) severely affected the genetic features of the species in the Cantabrian mountains. A consequence is that the eastern Cantabrian subpopulation shows some of the lowest genetic variation among brown bear populations in Europe (Swenson et al., ).…”

“…The European brown bear ( Ursus arctos arctos ) population located in the Cantabrian Range (northwestern Iberian Peninsula) represents the southwestern limit distribution for this species in Europe. As with other remnant ursid populations on the continent, it underwent a dramatic decline in the second half of the twentieth century (Martínez‐Cano, Taboada, Naves, Fernández‐Gil, & Wiegand, ). This decline, together with human‐caused mortality as a key factor (González et al., ; Naves, Wiegand, Fernández, & Stephan, ), reduced the Cantabrian brown bear population to a nadir of less than 100 individuals in the 1990s and divided it into two subpopulations (western and eastern) favoured by geographical barriers, thus putting the species in serious danger of extinction in the Cantabrian region (Wiegand, Naves, Stephan, & Fernández, ).…”