Homogenisation of carnivorous mammal ensembles caused by global range reductions of large-bodied hypercarnivores during the late Quaternary

Carnivorous mammals play crucial roles in ecosystems by
influencing prey densities and behaviour, and recycling carrion. Yet,
the influence of carnivores on global ecosystems has been affected by
extinctions and range contractions throughout the Late Pleistocene and
Holocene (~130 000 years ago to the current). Large-bodied mammals
were particularly affected, but how dietary strategies influenced
species’ susceptibility to geographic range reductions remains
unknown. We investigated 1) the importance of dietary strategies in
explaining range reductions of carnivorous mammals (≥5% vertebrate
meat consumption), and 2) differences in functional diversity of
continental carnivore ensembles by comparing current, known ranges to
current, expected ranges under a present-natural counterfactual
scenario. The present-natural counterfactual estimates current mammal
ranges had modern humans not expanded out of Africa during the Late
Pleistocene and were not a main driver of extinctions and range
contractions, alongside changing climates. Ranges of large-bodied
hypercarnivorous mammals are currently smaller than expected, compared
to smaller-bodied carnivorous mammals that consume less vertebrate
meat. This resulted in consistent differences in continental
functional diversity, whereby current ensembles of carnivorous mammals
have undergone homogenisation through structural shifts towards
smaller-bodied insectivorous and herbivorous species. The magnitude of
ensemble structural shift varied among continents, with Australia
experiencing the greatest difference. Weighting functional diversity
by species’ geographic range sizes caused a three-fold greater shift
in ensemble centroids than when using presence-absence alone.
Conservation efforts should acknowledge current reductions in the
potential geographic ranges of large-bodied hypercarnivores and aim to
restore functional roles in carnivore ensembles, where possible,
across continents.
Methods
(1) Range data/species-site matrix:

Data was initially accessed from the Phylogenetic Atlas of Mammals (Phylacine; Version 1.2) database: https://github.com/MegaPast2Future/PHYLACINE_1.2

Geographic range data, as rasters, were downloaded from Phylacine for the Current and Present-natural scenarios. All mammals had the values extracted from the raster layers and stored in columns to create a species-site matrix for all cells across the world. 

Each cell was identified as (1) belonging to a specific continent, and (2) whether it was attached to the mainland during the last glacial maximum (to identify islands to include).

(2) BBPMM model predictions on raw data

 Predictions from a Binomial Bayesian Phylogenetic Mixed Model (BBPMM) on species-range losses. 

Further methods in paper.

(3) Species' geographic range rasters

Methods in paper.