Science snippets: The Impact of Habitat Loss on Mammal Populations
By: Erin Adams and dr Lizanne Roxburgh
Habitat loss and degradation are among the leading causes of population decline for species worldwide. The main issue is the conversion of natural ecosystems to croplands, rangelands, forests and infrastructure. However, it has been difficult, up to now, to accurately assess on a large-scale what role habitat loss has played in the recent range declines of animal populations. In a recent publication, co-authored by EWT scientists*, they compared current and past (from the 1970s and 1980s) distribution ranges of mammals to understand the reasons as to why those ranges might be smaller today, and specifically whether their ranges are smaller due to habitat loss and degradation.
The scientists produced distribution maps for 475 land-dwelling mammals from 50 years ago – the “past range” – and for today – the “retained range”. By subtracting the two, they calculated what they called the “lost range”. They then compared the proportions of habitat available for the species in the lost range compared with the retained range. Habitat refers to areas suitable for the species to live in.
The scientists found that for 59% of species, their lost ranges have less habitat available to them compared to their retained ranges. This suggests that the ranges for these spaces have shrunk due to habitat loss.
The scientists also ran analyses in order to determine which factors influence the amount of habitat available. The most important factors that negatively affected habitat availability were conversion of land to rangeland and high density of livestock. Intensive livestock grazing reduces the amount of food available for herbivores and granivores, leads to changes in vegetation structure, which affects small mammals, and reduces the prey available for carnivores. This study shows the importance of protecting habitats from human activities in order to conserve remaining habitat. For those species where lost ranges have a similar amount of habitat left compared to retained ranges, this gives hope for species recovery if other threats, such as hunting and persecution, can be reduced.
*Pacifici, M., Cristiano, A., Lumbierres, M., Lucherini, M., Mallon, D., Meijaard, E., Solari, S., Tognelli, M. F., Belant, J. L., Butynski, T. M., Cronin, D., d’Huart, J.-P., Da Re, D., de Jong, Y. A., Dheer, A., Fei, Li, Gallina, S., Goodrich, J. M., Harihar, A. … Wiesel, I. (2023). Drivers of habitat availability for terrestrial mammals: Unravelling the role of livestock, land conversion and intrinsic traits in the past 50 years. Global Change Biology, 29, 6900–6911. https://doi.org/10.1111/gcb.16964