Abstract
Analysis of ecological time series allows to assess the relative contribution of density-dependent and density-independent factors influencing the regulation of the population of a species. In this study, we investigated whether the annual fluctuation in the population of Middle Spotted Woodpeckers Dendrocoptes medius can be attributed to the direct or delayed density-dependent regulation or to the density-independent factors such as weather conditions during the preceding winter and previous breeding season and/or disturbance in the habitat associated with sanitary felling and salvage logging of trees. This study was conducted in the Czeszewo Forest Reserve, which protects the remnants of semi-natural flood-plain forest, and in the Łówkowiec Forest, which is a managed oak-dominated stand, during 19 seasons (2001–2019). Time series diagnostic revealed that the growth rate of population of Middle Spotted Woodpecker in protected semi-natural riverine forest and in managed oak forest was determined by first-order negative feedback, suggesting an important role of direct density-dependent mortality in the regulation of an equilibrium in population size. The effect of density-dependent process varied between study sites, being lower in riverine forest, where population size has increased distinctly in recent years. In both study areas, we detected strong positive effects of wind chill temperature during the preceding winter on population growth rates. We did not find evidence for the assumption that the increase in population growth rate is affected by weather conditions in the previous breeding season and by the disturbance in the habitat associated with sanitary felling and salvage logging of trees. Our results suggest that Middle Spotted Woodpeckers can benefit from global climate warming by an enhanced rate of winter survival or an increase in the accessibility of food, e.g., insects and other arthropods. The lack of time-lag significant correlations between population fluctuations suggests local habitat conditions, e.g., forest management, can modify inter-annual variability in time series of the Middle Spotted Woodpecker.
Highlights
Long-term studies reveal the temporal fluctuations and trends affecting the size of the population in question (Royama 1992; White 2019)
The primary goal of an ecological time series analysis is to assess the relative contribution of endogenous and exogenous factors affecting the regulation of the population of a particular species (Berryman and Turchin 2001)
A linear regression analysis revealed that temporal trends in the abundance of Middle Spotted Woodpeckers in both study areas increased over time; only in the case of Czeszewo Forest Reserve (CFR), this trend was statistically significant (CFR: slope ± standard errors (SEs) = 0.605 ± 0.161, t = 3.77, df = 17, P = 0.002; LF: slope ± SE = 0.410 ± 0.230, t = 1.78, df = 17, P = 0.093) (Fig. 1)
Summary
Long-term studies reveal the temporal fluctuations and trends affecting the size of the population in question (Royama 1992; White 2019). The primary goal of an ecological time series analysis is to assess the relative contribution of endogenous (density-dependent) and exogenous (densityindependent) factors affecting the regulation of the population of a particular species (Berryman and Turchin 2001). A few studies have examined the long-term ecological time series by focusing only on density-independent factors, e.g., weather conditions during the winter and food supply during the spring, affecting population dynamics of woodpeckers (Nilsson et al 1992; Saari and Mikusiński 1996; Wesołowski and Tomiałojć 1997; Steen et al 2006; Selås et al 2008). Population fluctuations might be caused due to the interactions between exogenous influences and endogenous feedback mechanisms (Royama 1992; Sæther et al 2016)
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