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Quantifying the relative importance of natural and anthropogenic drivers of spatial variation in vulnerability to predict species extinction risk

Periodic Reporting for period 1 - DRIVE (Quantifying the relative importance of natural and anthropogenic drivers of spatial variation in vulnerability to predict species extinction risk)

Reporting period: 2016-10-01 to 2018-09-30

DRIVE arose from the need to understand global species extinction patterns, a societal major challenge. Current models predicting extinction risk show poor explanatory power. To overlook this, DRIVE focusses on populations instead of species, as a species extinction results from a sequence of local population extirpations. Population size and demography greatly determine tolerance to human impacts, and may vary geographically with environmental conditions. This variability can be considered as the intrinsic vulnerability of local populations to extirpation. Its existence has been confirmed for a few large mammals using biomes to define environmental conditions. This approach does not allow to assess this vulnerability for the majority of species. DRIVE aimed to quantify the relative importance of natural and anthropogenic factors in driving species inherent vulnerability, with the ultimate goal of including it as a key trait into models of extinction risk. Objectives were to 1) build a novel global biogeographic template for mammals to define small biogeographic regions (Obj 1); 2) find the determinants of these small biogeographic regions (Obj 2); 3) build models including small biogeographic regions as predictors to determine the role of natural and anthropogenic factors in the population extirpation risk (Obj 3); 4) build predictive models of extinction risk incorporating species inherent vulnerability. Conclusions so far: 1) the world’s biodiversity is organised with a hierarchical structure of global biogeographical patterns that include a local basis determined by multiple and spatially heterogeneous factors; 2) geological events that occurred over millions of years permeate from the largest to the smaller scales, yet understanding biogeographical delineations at more local scales requires determinants acting at multiple temporal and spatial scales; 3) the signal of Holocene anthropogenic impacts can be already detected in the configuration of realms, traditionally assumed to be the organisation of biodiversity from ecological, historical, and evolutionary processes over millions of years; 4) the amount of energy (in terms of biomass) left in the ecosystems after human harvesting is a better predictor of extinction risk than the direct human impact, which can be related to the energy that populations need to survive.
The Obj 1 has established a novel analytical protocol based on a clustering algorithm to generate a hierarchical system of biogeographical regions for mammals with four levels (1128, 141, 27 and 9 bioregions) showing that global biodiversity patterns can be cohesively shaped from local to regional and realm scales. These bioregions were used in the Obj 2 to identify the determinants that best predict taxonomic differences among bioregions within the framework of two hypothesised scenarios. Differentiation between large bioregions require longer evolutionary times, so both scenarios assume that historical determinants of speciation and extinction will be most important to explain taxonomic dissimilarities. As bioregions decrease in size processes related to tolerances to given habitats, past and present climates, and past and present human impact would gain importance. The scenarios differ in how this process may occur: linearly or nested. Models show the existence of a nested effect across time and space of the determinants tested. Events occurring millions of years ago, as tectonic movements or orographic barriers, remained apparent from the largest to the smallest bioregions, while recent past and current determinants acquired importance at smaller scales. For the smaller bioregions, a combination of multiple determinants, with a particular influence of Quaternary climate changes, was critical to predict biogeographical assemblages. Models also showed a prevalent footprint of past anthropogenic impacts, particularly human land use 2000 years ago, across the hierarchical bioregionalisation. Interestingly, this variable was the most important determinant behind the plate tectonics for the largest bioregions. On the contrary, current human land use was unimportant, consistent with the hypothesis that human impact has been extensive and started longer ago than is often recognised. So far, the Obj 3 has computed preliminary ecological models to assess the performance of the human appropriation of net primary productivity (HANPP) as a direct proxy of current human impacts predicting extinction risk. HANPP is an integrated socio-ecological indicator quantifying the effects of human-induced changes in productivity and harvest on ecological biomass flows. Models including HANPP were not good predicting extinction risk, but the alternatively use of the energy that remains in the system, in terms of biomass after the human harvest (NPP0) resulted successful to predict extinction risk. This unexpected result opens the door to new conservation-related questions to predict vulnerability to extinction risk. Actions carried out so far have allowed to increase the scientific impact of DRIVE by presenting the main results to some of the most relevant international meetings in biogeography and ecology (IBS meetings, MEDECOS). Data and results will be uploaded to the project website once accepted for publication.
Many analyses and writing are still on progress. Results so far have allowed to start new research lines beyond the state-of-the-art. So, the smaller bioregions (Obj 1) will be used as surrogates of ecological communities to assess global species interaction networks. Results from Obj.3 has resulted in a new line related to the characteristics of the areas protected within the species ranges. As the NPP0 of the system has resulted so important to predict the extinction risk, we wonder whether we are protecting areas with higher or lower NPP0. Also, as part of a PhD thesis NPP0 is being used to create a metric of biodiversity threat useful to assess total risk impact. As NPP0 can be obtained for the majority of species we can know the threat status of a large number of data deficient species that currently have not been assigned an IUCN category due to lack of information. The results obtained so far, together with those expected soon, make DRIVE maintains a high socio-economic impact and with wider societal implications. Basically, the society is becoming increasingly aware that global biodiversity loss is altering the functioning of Earth's ecosystems and their ability to provide the services needed to prosper. So, to understanding species extinction patterns is critical (Results from WP2), and for this it is essential first knowing how the world's biodiversity is organised, why large-scale patterns of taxonomic diversity change through natural geographic regions, and which are the determinants of the biodiversity organisation (Results from WP1). Only by knowing the present and past determinants of the organisation of species, can we predict shifts in the current distribution of species (and their risk of extinction) in the face of global change. Moreover, the potential results that are expected from WP2 will allow knowing in detail which populations are more in danger of becoming extinct in the European area. Altogether, results from this Action can help to solve problems that the European society demands.
Hypothesized scenarios and most important determinants of bioregions across the hierarchical scale
Hierarchical global bioregionalisation for terrestrial mammals