Stefanie Deinet

Predicting how populations decline to extinction

Global species extinction typically represents the endpoint in a long sequence of population declines and local extinctions. In comparative studies of extinction risk of contemporary mammalian species, there appear to be some universal traits that may predispose taxa to an elevated risk of extinction. In local population-level studies, there are limited insights into the process of population decline and extinction. Moreover, there is still little appreciation of how local processes scale up to global patterns. Advancing the understanding of factors which predispose populations to rapid declines will benefit proactive conservation and may allow us to target at-risk populations as well as at-risk species. Here, we take mammalian population trend data from the largest repository of population abundance trends, and combine it with the PanTHERIA database on mammal traits to answer the question: what factors can be used to predict decline in mammalian abundance? We find in general that environmental variables are better determinants of cross-species population-level decline than intrinsic biological traits. For effective conservation, we must not only describe which species are at risk and why, but also prescribe ways to counteract this.

The Diversity-Weighted Living Planet Index: Controlling for Taxonomic Bias in a Global Biodiversity Indicator

As threats to species continue to increase, precise and unbiased measures of the impact these pressures are having on global biodiversity are urgently needed. Some existing indicators of the status and trends of biodiversity largely rely on publicly available data from the scientific and grey literature, and are therefore prone to biases introduced through over-representation of well-studied groups and regions in monitoring schemes. This can give misleading estimates of biodiversity trends. Here, we report on an approach to tackle taxonomic and geographic bias in one such indicator (Living Planet Index) by accounting for the estimated number of species within biogeographical realms, and the relative diversity of species within them. Based on a proportionally weighted index, we estimate a global population decline in vertebrate species between 1970 and 2012 of 58% rather than 20% from an index with no proportional weighting. From this data set, comprising 14,152 populations of 3,706 species from 3,095 data sources, we also find that freshwater populations have declined by 81%, marine populations by 36%, and terrestrial populations by 38% when using proportional weighting (compared to trends of -46%, +12% and +15% respectively). These results not only show starker declines than previously estimated, but suggests that those species for which there is poorer data coverage may be declining more rapidly.

The Arctic Species Trend Index: using vertebrate population trends to monitor the health of a rapidly changing ecosystem

The task of measuring the change of Arctic biodiversity and instituting changes to halt and reverse any downturn has been taken up in response to the rapid changes observed in the region. It is an undertaking made more difficult by the rate at which environmental change is occurring and the difficulty in monitoring species in remote and challenging habitats. We explored techniques to aggregate population trends among vertebrate species. We compiled almost 900 time series data sets tracking trends in Arctic vertebrate populations over the past four decades representing 37% of all known Arctic vertebrate species. Our results showed strengths in the breadth of populations and species monitored and the disaggregation of the data to uncover regional trends. Limitations of the data set were still apparent, due to the lack of any stratified monitoring scheme. Specifically, there were more bird species data than any other vertebrate class. To measure progress towards global targets for the environment, such as the Aichi biodiversity targets for the Convention on Biological Diversity (CBD), indicators like the one we have developed must be strengthened and adapted. Never has it been more important to understand how Arctic ecosystems and the living resources they support are responding to environmental change; tracking how they respond to growing and cumulative pressures will enable pre-emptive action to safeguard their future.