Invasive Species

ARMI conducts research on the ecology of invasives, their impacts on native species, and how invasive species can be reduced or eradicated. Habitat used by amphibians has been exposed to many types of invasives through deliberate or accidental introductions. For example, sport fish deliberately introduced to ponds and streams in the western US that were formerly fishless, have been associated with the loss of amphibians in those water bodies. In another example, the American bullfrog of the Eastern US was introduced into the Western US through a combination of introductions into ponds for bait, and escapes from frog farms. The American bullfrog has been a relentless predator of several species already in conservation trouble in the Western US.

What types of problems do invasive species cause?
Some species harm native species directly by preying on them or competing with them for resources, and some modify or destroy the habitat used by native species.

Where do invasive species come from?
Some come from deliberate introductions such as biological control, stocking for hunting, fishing, or spreading bait species. Some are accidental escapes from pet stores, farming/aquaculture facilities, and ornamental gardens. Some animals are released by pet owners or teaching labs. Some species hitchhike with materials otherwise deliberately moved such as garden plants, ballast water, boats and nets.

Feral hogs.
Feral hogs trapped at St Marks NWR, FL. Photo by: W. Barichovich.

Terms Related to Invasive Species

Invasive species: Plant, animal or pathogen that is not native to an area, and "whose introduction does or is likely to cause economic or environmental harm or harm to human health." [US Executive Order 13112. 1999]

Injurious Wildlife (defined by Lacey Act) - Mammals, birds, amphibians, reptiles, fish, crustaceans, mollusks and their offspring or gametes that are injurious to the interests of human beings, agriculture, horticulture, forestry, wildlife or wildlife resources of the United States. Plants and organisms other than those listed above cannot be listed as injurious wildlife.

Nonindigenous species: Any species or other viable biological material that enters an ecosystem beyond its historic range, including any such organism transferred from one country into another. (Nonindigenous Aquatic Nuisance Prevention and Control Act of 1990)

Aquatic nuisance species: A nonindigenous species that threatens the diversity or abundance of native species or the ecological stability of infested waters, or commercial, agricultural, aquacultural or recreational activities dependent on such waters. (Nonindigenous Aquatic Nuisance Prevention and Control Act of 1990)


Invasive Species - ARMI Papers & Reports

Papers & Reports Resilience of native amphibian communities following catastrophic drought: evidence from a decade of regional-scale monitoring
Authors: W Moss; T McDevitt-Galles; Erin L Muths; Steven Bobzien; J Purificato; P TJ Johnson
1. The increasing frequency and severity of drought has the potential to exacerbate existing global amphibian declines. However, interactions between drought and coincident stressors, coupled with high interannual variability in amphibian abundances, can mask the extent and underlying mechanisms of drought-induced declines. The application of dynamic occupancy modeling to longitudinal monitoring data estimates the effect of specific variables on population change, providing key insights into potential management strategies for drought resilience.
2. We synthesized a decade (2009 – 2019) of amphibian survey data from multiple monitoring programs across the California Bay Area and used occupancy modeling to estimate the influence of drought, invasive species, and land use on species’ persistence and colonization probabilities. The geographic and temporal scale of our dataset, consisting of 2574 surveys of seven species in 473 ponds, allowed us to quantify regional trends for an entire community of pond-breeding amphibians.
3. An extreme drought from 2012 – 2015 resulted in losses of breeding sites, with 51% of ponds drying in 2014 compared to <10% in non-drought years. Pond drying reduced persistence rates, and nearly every species exhibited reduced occupancy during the drought, with some species (American bullfrogs and California newts) declining by > 25%. Drought reduced occupancy via additional mechanisms beyond habitat loss; for example, lower spring precipitation (an important cue for breeding) was associated with reduced colonization.
4. During drought, native species’ persistence was higher in permanent relative to temporary ponds, even though these sites were also more likely to contain invasive fish and bullfrogs, which generally reduced native amphibian occupancy. Many of these permanent ponds dried during the worst year of drought, leading to extirpations of invasive species that appeared long-lasting. In contrast, native species rebounded quickly with returning rains and showed evidence of full recovery.
5. Synthesis and applications: Despite experiencing one of most severe droughts in a millennium, native species displayed high resilience. Due to longer recovery times by non-native relative to native species, drought presents a valuable management opportunity to remove invaders from key refugia, and we highlight the value of maintaining hydroperiod diversity to promote the persistence of multiple species.
Papers & Reports Widespread Ranavirus and Perkinsea infections in Cuban Treefrogs (Osteopilus septentrionalis) invading New Orleans, USA
Authors: N Galt; Matthew S Atkinson; Brad M Glorioso; J Hardin Waddle; M Litton; Anna E Savage
Date: 2021-04-30 | Outlet: Herpetological Conservation and Biology
Papers & Reports When Introduced Prey Violates Trophic Hierarchy: Conservation of an Endangered Predator
Authors: Richard Kim; Brian J Halstead; E Routman; Julie Andersen
Date: 2021-03-03 | Outlet: Biological Conservation 256
Introduced species often disrupt established food webs, but some native predators can come to rely on introduced prey. Understanding the net effects of the non-natives on imperiled predators is crucial for planning conservation measures. The invasive American bullfrog (Lithobates catesbeianus) can be prey, predator, and competitor for the critically endangered San Francisco garter snake (Thamnophis sirtalis tetrataenia). We examined the seasonal prey use of a San Francisco garter snake population that co-occurs with American bullfrogs to examine intraguild predation between these species. Juvenile and adult snakes mainly consumed native anurans instead of American bullfrogs, and this diet pattern peaked in spring, a critical foraging period for the snakes. In spring, large adult American bullfrogs also foraged heavily on native anurans and displayed a high degree of diet overlap with San Francisco garter snakes. Invasive American bullfrogs are detrimental to San Francisco garter snakes mainly through seasonal competition rather than reciprocal predation. Removal of invasive species provided further evidence that eliminating American bullfrogs can benefit San Francisco garter snakes by reducing predation pressure on their shared amphibian prey. Better understanding the interactions of invasive species with native species of conservation concern informs management practices and improves conservation outcomes.
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