Ecological function maintained despite mesomammal declines

Abstract

Mid-sized mammals (i.e., mesomammals) fulfill important ecological roles, serving as essential scavengers, predators, pollinators, and seed dispersers in the ecosystems they inhabit. Consequently, declines in mesomammal populations have the potential to alter ecological processes and fundamentally change ecosystems. However, ecosystems characterized by high functional redundancy, where multiple species can fulfil similar ecological roles, may be less impacted by the loss of mesomammals and other vertebrates. The Greater Everglades Ecosystem in southern Florida is a historically biodiverse region that has recently been impacted by multiple anthropogenic threats, most notably the introduction of the Burmese python (Python molurus bivittatus). Since pythons became established, mesomammal populations have become greatly reduced. To assess whether these declines in mesomammals have affected two critical ecosystem functions-scavenging and frugivory-we conducted experiments in areas where mesomammals were present and absent. We did not observe significant differences in scavenging or frugivory efficiency in areas with and without mesomammals, but we did observe significant differences in the communities responsible for scavenging and frugivory. Despite the observed evidence of redundancy, the changes in community composition could potentially lead to indirect consequences on processes like seed dispersal and disease dynamics within this ecosystem, emphasizing the need for further study.

Figure 1

Map of python removals that occurred between 1979 and 2019 across Florida with study region in Greater Everglades Ecosystem outlined in turquoise. Inset: Map of 15 sampling sites on public lands within the GEE study region. Mesomammals were detected at all 15 sites in 2014 surveys but were detected at only 9 of 15 locations in the sampling conducted in 2019. This figure was created using ArcGIS Pro 3.1.0 (https://www.esri.com/en-us/arcgis/products/arcgis-pro/overview).

Figure 2

(a) Scavenging and (b) frugivory station stations deployed at 15 sites in the Greater Everglades Ecosystem (Florida, USA). Scavenging stations were baited with two rat carcasses. Frugivory stations included the fruit of three native species, American beautyberry, cocoplum, and pond apple.

Figure 3

Cox proportional hazards survival curves with 95% confidence intervals representing the probability that (a) the carcass remained unvisited; (b) the carcass was not completely consumed; and (c) that fruit remained unvisited as a function of hours since station placement. Line color reflects whether mesomammals were detected or not detected at the site in passive sampling.

Figure 4

Number of (a) scavenging and (b) frugivory bouts by group in sites where mesomammals were detected versus not detected in passive surveys conducted at 15 sites in the Everglades (Florida, USA). A single scavenging bout by a bear was also recorded at a site where mesomammals were not detected but is not represented in the figure.

Figure 5

Proportion of each fruit type, beautyberry (BB), cocoplum (CP), and pond apple (PA) consumed during frugivory experiments. Error bars indicate standard deviation.