Introduced herbivores restore Late Pleistocene ecological functions

Abstract

Large-bodied mammalian herbivores dominated Earth’s terrestrial ecosystems for several million years before undergoing substantial extinctions and declines during the Late Pleistocene (LP) due to prehistoric human impacts. The decline of large herbivores led to widespread ecological changes due to the loss of their ecological functions, as driven by their unique combinations of traits. However, recently, humans have significantly increased herbivore species richness through introductions in many parts of the world, potentially counteracting LP losses. Here, we assessed the extent to which introduced herbivore species restore lost—or contribute novel—functions relative to preextinction LP assemblages. We constructed multidimensional trait spaces using a trait database for all extant and extinct mammalian herbivores ≥10 kg known from the earliest LP (∼130,000 ybp) to the present day. Extinction-driven contractions of LP trait space have been offset through introductions by ∼39% globally. Analysis of trait space overlap reveals that assemblages with introduced species are overall more similar to those of the LP than native-only assemblages. This is because 64% of introduced species are more similar to extinct rather than extant species within their respective continents. Many introduced herbivores restore trait combinations that have the capacity to influence ecosystem processes, such as wildfire and shrub expansion in drylands. Although introduced species have long been a source of contention, our findings indicate that they may, in part, restore ecological functions reflective of the past several million years before widespread human-driven extinctions.

Mammalian herbivory shapes intraspecific trait responses to warmer climate and nutrient enrichment

“…Furthermore, herbivory also affected how intraspecific trait plasticity translates to changes in relative abundance in a community. These results suggest that decisions on management and regulation of grazer and predator populations play critical roles in altering trait change in tundra and its consequences on ecosystem functioning in the Anthropocene (Bakker & Svenning, 2018; Estes et al., 2011; Lundgren et al., 2020).…”

Trophic rewilding presents regionally specific opportunities for mitigating climate change

“…In total, 506 large-bodied (greater than or equal to 10 kg) and predominantly herbivorous (greater than or equal to 50% plant diet) species were identified and included in the study. Functional trait data on herbivore digestive physiology and diet were derived from a comprehensive new database compiled by the authors [30] (see electronic supplementary material, appendix A for data on species included in this study). Species range maps were used to create three mammal distribution scenarios: (i) Present-Natural, which included all extant and extinct wild species over their presentnatural range, i.e.…”

Megafauna extinctions have reduced biotic connectivity worldwide

“…Moreover, average movement capacity will decrease further in South America if possible future extinctions are not averted, because four threatened megafauna species ( Hippocamelus antisensis , Hippocamelus bisulcus , Priodontes maximus and Tremarctos ornatus ) are responsible for promoting a relatively large proportion of the mobility of current assemblages (considering only the native species, cf. Lundgren et al, 2020). In Europe, megafauna extinctions have not been so severe compared with the Americas, and many megafauna species have survived in parts of their former ranges.…”

“…This result is probably biased by inaccuracies in the distribution maps of Australian mammals in the PHYLACINE database caused by sampling artefacts, probably underestimating the geographical ranges of species (Faurby & Svenning, 2015). As a result of adverse environmental factors, estimates of megafauna present‐natural ranges are restricted to the relatively small, humid parts of Australia, an overly conservative estimation of their ranges, because large mammals today live in more arid Australian regions (Lundgren et al, 2020). Hence, in our model the almost complete eradication of megafauna in Australia has not resulted in an equally severe decrease in the movement capacity of mammal assemblages on the continent.…”

“…Like Europe and the Americas, the introduction of suitable non‐native species as ecological replacements for extinct megafauna will be the only available option for full restoration of the movement capacity of terrestrial mammal assemblages (Jarvie & Svenning, 2018; Svenning et al, 2016). Notably, introduced feral species, which are not included in the PHYLACINE ranges, such as the dromedary ( Camelus dromedarius ), might already act as ecological replacements for the extinct native megafauna (Lundgren et al, 2020), increasing the movement capacity of assemblages and promoting connectivity among ecosystems (Muñoz‐Gallego, Traveset, & Fedriani, 2019).…”