Trends in mean growth and stability in temperate vertebrate populations

Abstract

Aim: Considerable controversy exists over the nature of the "Biodiversity Crisis."While some studies suggest declining diversity, others suggest no loss on average.Population declines necessarily precede species loss and may therefore be a more sensitive metric. We examine trends in abundances to test the hypotheses: (1) losses are experienced disproportionately by some taxa, in particular amphibians; (2) positive trends in alien or unexploited species mask declines in native or exploited species, respectively; (3) populations are becoming more unstable, and variances of withinpopulation growth rates are increasing. Location: Freshwater and terrestrial habitats in North America and Europe.Methods: We analysed abundances of 4,343 population time series of 983 species of temperate amphibians, birds, bony fishes, reptiles and mammals from 1970 to 2014.Population mean trends were estimated using a state-space model to account for observation error, and then, linear mixed-effects models were used to test mean differences among groups. As a measure of instability, trends over time in variance of population growth rates were analysed using a Breusch-Pagan test for heteroscedacity, and integrated across populations using meta-analysis.Results: Mean trends for amphibians suggested a systematic decline, whereas birds, reptiles and mammals were increasing, on average, and freshwater fishes showed no net change in general. Origin and exploitation status did not explain the mean patterns. Large-bodied birds and range-restricted mammals exhibited stronger increases compared to their counterparts. For all taxonomic groups, population fluctuations have been increasing overall. Main conclusions:Addressing amphibian declines should be a priority in temperate regions. Comparatively, the lack of broad declines in the other vertebrate classes is promising and not attributable to increases in alien or non-exploited species. Yet, caution remains warranted given that patterns of increasing variance suggested that populations are generally becoming more unstable, even in temperate, developed nations, with arguably the strongest environmental regulations. K E Y W O R D Samphibian declines, biodiversity crisis, ecological instability, population trends, temperate biodiversity, vertebrate conservation | 1373 LEUNG Et aL.

Landscape-scale forest loss as a catalyst of population and biodiversity change

“…Losses in species richness lagged behind richness gains by only approximately half a year (slope = 0.5, CI = 0.1 -1.05), indicating that extinction debts and immigration credits accumulated at 225 roughly the same speed across taxa. The similar pace and temporal delay of population declines and increases, and richness gains and losses could be a contributing factor towards previous findings of no net population change (2,9,43) and richness change (4, 5) at local scales, in line with community self-regulation (17). Temporal lags in biodiversity change have also been 14 observed in post-agricultural forests (3,44) and fragmented grasslands (30), where agricultural 230 activity has ceased decades to centuries ago, yet richness and community composition change continue to the modern-day.…”

“…The abundance of species' 40 populations (2) and the richness (3)(4)(5) and composition (5) of ecological assemblages at sites around the world are being altered over time in complex ways (6)(7)(8). However, we currently have only a limited quantitative understanding of how global change drivers, such as land-use change, produce heterogeneous local-scale patterns in population abundance and biodiversity over time (7,9,10), as highlighted by the recent IPBES Global Assessment (1). In terrestrial ecosystems, much 45 of our current knowledge stems from space-for-time (11,12) and modelling projection approaches (13,14) that attribute population and richness declines to different types of land-use change, including reductions in forest cover.…”

A balance of winners and losers in the Anthropocene

“…) or a slight overall preponderance of winners over losers in North America and Europe (Leung et al . ).…”

“…However, in the one group where a majority of species were studied (58% of all vertebrates studied) almost 60% of species increased (were winners). Two large studies also of vertebrates, a very wellsampled group, found a balance between winners and losers at both the global and UK scales (Daskalova et al 2018) or a slight overall preponderance of winners over losers in North America and Europe (Leung et al 2017).…”

Changes in the diet and body size of a small herbivorous mammal (hispid cotton rat,Sigmodon hispidus) following the late Pleistocene megafauna extinction

“…State-space models are therefore useful for data that have variation in the distribution of residuals and the potential for the non-independence of variables to change across a time series (Commandeur and Koopman 2007). State-space models have been employed in ecology to consider changes in population dynamics and biodiversity in a variety of vertebrates (Flowerdew et al 2017, Leung et al 2017, Rogers et al 2017, as well as in economics (Harvey 1990, Kim and Nelson 1999, Durbin and Koopman 2001. We used a stochastic local level and slope model allowing the importance of each explanatory variable to vary at each time point, to account for the fact that each variable may be having larger or smaller effects on the response due to the range and grouping of data values within our time bins.…”