Estimating Wolf Population Size and Dynamics by Field Monitoring and Demographic Models: Implications for Management and Conservation

We estimated the current size and dynamics of the wolf population in Tuscany and investigated the trends and demographic drivers of population changes. Estimates were obtained by two different approaches: (i) mixed-technique field monitoring (from 2014 to 2016) that found the minimum observed pack number and estimated population size, and (ii) an individual-based model (run by Vortex software v. 10.3.8.0) with demographic inputs derived from a local intensive study area and historic data on population size. Field monitoring showed a minimum population size of 558 wolves (SE = 12.005) in 2016, with a density of 2.74 individuals/100 km2. The population model described an increasing trend with an average annual rate of increase λ = 1.075 (SE = 0.014), an estimated population size of about 882 individuals (SE = 9.397) in 2016, and a density of 4.29 wolves/100 km2. Previously published estimates of wolf population were as low as 56.2% compared to our field monitoring estimation and 34.6% in comparison to our model estimation. We conducted sensitivity tests to analyze the key parameters driving population changes based on juvenile and adult mortality rates, female breeding success, and litter size. Mortality rates played a major role in determining intrinsic growth rate changes, with adult mortality accounting for 62.5% of the total variance explained by the four parameters. Juvenile mortality was responsible for 35.8% of the variance, while female breeding success and litter size had weak or negligible effects. We concluded that reliable estimates of population abundance and a deeper understanding of the role of different demographic parameters in determining population dynamics are crucial to define and carry out appropriate conservation and management strategies to address human-wildlife conflicts.

Immature survival, fertility, and density dependence drive global population dynamics in a long-lived species

Disentangling the influence of demographic parameters and the role of density dependence on species' population dynamics is a challenge, especially when fractions of the population are unobservable. Additionally, due to the difficulty of gathering data at large spatial scales, most studies ignore the global dynamic of a species, which would integrate local heterogeneity dynamics and remove the noise of dispersal. We developed an integrated population model (IPM) at a global scale to disentangle the main demographic drivers of population dynamics in a long-lived species. We used 28 yr of Audouin's Gull demographic data encompassing 69 local patches (comprising 90% of the world population). Importantly, we took into account the unobservable fraction of non-breeders and also assessed the strength of density dependence for this fraction of the population. As predicted by life histories of long-lived organisms, temporal random variation in survival was highest for immature individuals (1.326, 95% credible interval [CRI] 1.290-1.940) and lowest for adults (0.499, 95% CRI 0.487-0.720). Large temporal fluctuations in the probability of taking a reproductive sabbatical would partly explain the consistency in adult survival, with individuals most likely refraining from breeding when environmental conditions were harsh. Immature survival and fertility were the main drivers of population dynamics during the study period (r²  = 0.83, 0.77-0.87 and 0.73, 0.63-0.79, respectively). We found strong evidence of density dependence, not only due to the number of breeders (r²  = -0.34, -0.43 to -0.24) but also due to individuals on sabbatical (r²  = -0.18, -0.33 to -0.01). From a conservation point of view, the species shows a 5% annual global decrease during the last 10 years, and we propose an update of its conservation status. Even though population dynamics of long-lived organisms are very sensitive to changes in adult survival, we show here that, in the absence of strong environmental perturbations affecting this vital rate, fluctuations in population density are mainly driven by variations in survival of immature individuals and fertility. Integrated models based on long-term monitoring at a global scale may enhance our ecological and evolutionary understanding of how demographic drivers influence population dynamics.

The limited contribution of large trees to annual biomass production in an old-growth tropical forest

Although the importance of large trees regarding biodiversity and carbon stock in old-growth forests is undeniable, their annual contribution to biomass production and carbon uptake remains poorly studied at the stand level. To clarify the role of large trees in biomass production, we used data of tree growth, mortality, and recruitment monitored during 20 yr in 10 4-ha plots in a species-rich tropical forest (Central African Republic). Using a random block design, three different silvicultural treatments, control, logged, and logged + thinned, were applied in the 10 plots. Annual biomass gains and losses were analyzed in relation to the relative biomass abundance of large trees and by tree size classes using a spatial bootstrap procedure. Although large trees had high individual growth rates and constituted a substantial amount of biomass, stand-level biomass production decreased with the abundance of large trees in all treatments and plots. The contribution of large trees to annual stand-level biomass production appeared limited in comparison to that of small trees. This pattern did not only originate from differences in abundance of small vs. large trees or differences in initial biomass stocks among tree size classes, but also from a reduced relative growth rate of large trees and a relatively constant mortality rate among tree size classes. In a context in which large trees are increasingly gaining attention as being a valuable and a key structural characteristic of natural forests, the present study brought key insights to better gauge the relatively limited role of large trees in annual stand-level biomass production. In terms of carbon uptake, these results suggest, as already demonstrated, a low net carbon uptake of old-growth forests in comparison to that of logged forests. Tropical forests that reach a successional stage with relatively high density of large trees progressively cease to be carbon sinks as large trees contribute sparsely or even negatively to the carbon uptake at the stand level.

The Role of Policy and Institutions on Health Spending

This paper investigates the impact of policies and institutions on health expenditures for a large panel of Organisation for Economic Co-operation and Development countries for the period of 2000-2010. A set of 20 policy and institutional indicators developed by the Organisation for Economic Co-operation and Development are integrated into a theoretically motivated econometric framework, alongside control variables related to demographic (dependency ratio) and non-demographic (income, prices and technology) drivers of health expenditures per capita. Although a large share of cross-country differences in public health expenditures can be explained by demographic and economic factors (around 71%), cross-country variations in policies and institutions also have a significant influence, explaining most of the remaining difference in public health spending (23%). Copyright © 2016 John Wiley & Sons, Ltd.