Functional traits-not nativeness-shape the effects of large mammalian herbivores on plant communities.

Large mammalian herbivores (megafauna) have experienced extinctions and declines since prehistory. Introduced megafauna have partly counteracted these losses yet are thought to have unusually negative effects on plants compared with native megafauna. Using a meta-analysis of 3995 plot-scale plant abundance and diversity responses from 221 studies, we found no evidence that megafauna impacts were shaped by nativeness, "invasiveness," "feralness," coevolutionary history, or functional and phylogenetic novelty. Nor was there evidence that introduced megafauna facilitate introduced plants more than native megafauna. Instead, we found strong evidence that functional traits shaped megafauna impacts, with larger-bodied and bulk-feeding megafauna promoting plant diversity. Our work suggests that trait-based ecology provides better insight into interactions between megafauna and plants than do concepts of nativeness.

Shallow size-density relations within mammal clades suggest greater intra-guild ecological impact of large-bodied species.

Population densities of species have a predictable relationship with their body mass on a global scale. This relationship is known as the size-density relationship (SDR). The relationship was originally found to be directly opposite of metabolic rate scaling, which led to the hypothesis of energetic equivalence. However, recent studies have suggested that the SDR varies between clades. Specifically, the SDR for certain mammal clades has been found to be less negative than the relationship across all mammals. The aim of the present study is to estimate phylogenetic variation in the scaling relationship, using a data-driven identification of natural phylogenetic substructure in the body size-density relation, and discuss its potential drivers. The classic model is often used to estimate natural population densities, and a further, practical aim is to improve it by incorporating variability among phylogenetic groups. We expand the model for the SDR relation of mammals to include clade-specific variation. We used a dataset with population and body mass estimates of 924 terrestrial mammal species, covering 97 families, and applied an algorithm identifying group-specific changes in the relationship across a family-level phylogeny. We show increased performance in species density estimation is achieved by incorporating clade-specific changes in the relationship compared to the classic model (increasing r2 from .56 to .74 and ΔAICc  = 466). While the global SDR across clades was confirmed to be similar to previous findings (r = -.74), the relationship within all sub-clades was less negative than the overall trend. Our results show that data-driven identification of phylogenetic substructure in the size-density relation substantially improves predictive accuracy of the model. The less negative relationship within clades compared to the overall trend and compared to within clade metabolic scaling suggest that the energetic equivalence rule does not hold. This relationship shows that large species within clades use proportionally more energy than smaller species. Therefore, our results are consistent with a greater intra-guild ecological impact of large-bodied species via partial monopolisation of resources by the largest species of a given guild, and hence size-asymmetric intra-guild competition.

Macroecological evidence for competitive regional-scale interactions between the two major clades of mammal carnivores (Feliformia and Caniformia).

Geographical gradients in species diversity are often explained by environmental factors such as climate and productivity. Biotic interactions play a key role in evolutionary diversification and may therefore also affect diversity patterns, but this has rarely been assessed. Here, we investigate whether negative competitive interactions shape the diversity patterns of the two major mammalian clades of carnivores, the suborders Caniformia (dogs and allies) and Feliformia (cats and allies) within the order Carnivora. We specifically test for a negative effect of feliform species richness on caniform species richness by a natural experiment, The Great American Interchange, which due to biogeographic lineage history and climate patterns caused tropical South America to be colonized by most caniform families, but only one feliform family. To this end we used regression modelling to investigate feliform and caniform richness patterns and their determinants with emphasis on contrasting the Old and New World tropics. We find that feliform richness is elevated in the Old World Tropics, while caniform richness is elevated in the New World Tropics. Models based on environmental variables alone underpredict caniform richness and overpredict feliform richness in the New World and vice versa in the Old World. We further show that models including feliform richness as a predictor for caniform species richness significantly improve predictions at the continental scale, albeit not at finer scales. Our results are consistent with a negative effect of feliforms on regional-scale caniform diversification within the tropics, probably indicating that niche space occupancy by the one clade constrains diversification in the other in the build-up of regional faunas, while negative interactions at smaller scales may be unimportant due to niche differentiation within the regional faunas.