Severe mammal declines coincide with proliferation of invasive Burmese pythons in Everglades National Park

Abstract

Invasive species represent a significant threat to global biodiversity and a substantial economic burden. Burmese pythons, giant constricting snakes native to Asia, now are found throughout much of southern Florida, including all of Everglades National Park (ENP). Pythons have increased dramatically in both abundance and geographic range since 2000 and consume a wide variety of mammals and birds. Here we report severe apparent declines in mammal populations that coincide temporally and spatially with the proliferation of pythons in ENP. Before 2000, mammals were encountered frequently during nocturnal road surveys within ENP. In contrast, road surveys totaling 56,971 km from 2003-2011 documented a 99.3% decrease in the frequency of raccoon observations, decreases of 98.9% and 87.5% for opossum and bobcat observations, respectively, and failed to detect rabbits. Road surveys also revealed that these species are more common in areas where pythons have been discovered only recently and are most abundant outside the python's current introduced range. These findings suggest that predation by pythons has resulted in dramatic declines in mammals within ENP and that introduced apex predators, such as giant constrictors, can exert significant top-down pressure on prey populations. Severe declines in easily observed and/or common mammals, such as raccoons and bobcats, bode poorly for species of conservation concern, which often are more difficult to sample and occur at lower densities.invasion biology | population declines | top-down regulation | reptiles

Parasite spillover: indirect effects of invasive Burmese pythons

“…Direct effects of biological invasions are well documented (e.g., biodiversity loss, predation, and competition; Dorcas et al., 2012; Human & Gordon, 1996; Mooney & Cleland, 2001; Simberloff et al., 2013; Wilcove Rothstein, Dubow, Phillips, & Losos, 1998), but indirect effects, including alteration of host–parasite dynamics, may also profoundly affect an invaded ecosystem (Hoyer et al 2017; Willson 2017; Dunn et al., 2012 Rogers et al., 2017; Tompkins & Poulin, 2006). Nonindigenous species (NIS) often contain half the parasite species richness of conspecifics in their native range (MacLeod, Paterson, Tompkins, & Duncan, 2010; Torchin, Lafferty, Dobson, McKenzie, & Kurtis, 2003), but still, native hosts are at risk of infection by these non‐native parasites (i.e., spillover; Daszak, Cunningham, & Hyatt, 2000; Tompkins & Poulin, 2006).…”

Marsh rabbit mortalities tie pythons to the precipitous decline of mammals in the Everglades

“…The ecological processes, functionality and restoration efforts within this distinct ecosystem are probably being substantially impaired by the disappearance of once common mammalian predators and herbivores [4][5][6]. Declines in mammal populations in ENP appear to coincide temporally and spatially with the arrival and spread of invasive Burmese pythons [2], a large-bodied snake native to southeast Asia that preys on vertebrates. Pythons were probably introduced into ENP several decades ago via releases or escapes from private ownership [7].…”

“…One particularly contentious debate is over the role of the invasive Burmese python (Python molurus bivittatus or Python bivittatus) in the drastic declines of mammal populations in Everglades National Park (ENP) over the last several decades [2]. ENP, globally recognized for its unique biotic communities, sits at the southern end of the Greater Everglades Ecosystem (GEE), a vast freshwater wetland (%10 000 km 2 ) encompassing most of the southern Florida peninsula [3].…”

“…Pythons were probably introduced into ENP several decades ago via releases or escapes from private ownership [7]. Sightings and removals of pythons in ENP were sporadic in the 1980s and 1990s, increasing sharply in the early 2000s [2]. During this time, gut content analysis of invasive pythons in ENP indicated that mammals accounted for about 75% of their diet [8].…”

Weighing empirical and hypothetical evidence for assessing potential invasive species range limits: a review of the case of Burmese pythons in the USA

“…The Burmese python (Python molurus bivittatus), a well-established exotic species in the Everglades region of extreme southern Florida, is considered a major invasive species threat due to its large adult size (potentially >5 m) and the wide ranges in size and diversity of species as potential prey. These top-order carnivores are suspected of having serious impacts to native fauna, including endangered species, in the Everglades region (Dorcas et al 2012;Dove et al 2011;Greene et al 2007;Snow et al 2007a). Predicting the range expansion potential of the Burmese python can illuminate the potential breadth and magnitude of its impacts beyond South Florida.…”