Combating Invasives to Give Native Species Back Their Competitive Edge

When you visit a new country, chances are you don’t want to eat at the same burger chain you have near your house, buy your souvenirs at a big box store from the US, and go to an American movie. You want to experience the cuisine, hear the language, and see the art that that particular country offers because those things reveal the fabric of a place’s history and culture. 

We can use this concept to understand native ecosystems and invasive species. Just like you can find American burger chains around the world, there aren’t many ecosystems left that haven’t been impacted by invasive species. As humans have spread across the globe, we’ve taken all sorts of species with us—from house cats to flowers to reptiles—and put them where they didn’t historically occur. That has caused problems for our native species (the locals, if you will), and we are at risk of homogenizing our ecosystems and losing the icons of our natural diversity.

Areas, like the Everglades, that were once overflowing with a rich variety of plants and wildlife have been taken over by species that escaped or were intentionally moved there. In many cases, the native species are still present but in drastically reduced numbers, and that loss means that these places have far less of the creatures and plants that made them unique and beautiful. Plus, we can lose the function of an ecosystem, and a place can face new threats that weren’t an issue before. 

Invasive species include any kind of living thing that has been introduced and disrupts native species. Usually, they are habitat generalists that are adaptable and can reproduce quickly. Some of the better-known invasive species, like the Burmese python in Florida, impact ecosystems by outcompeting the native species and disrupting the food chain. Others have more subtle but equally cascading effects. The bottom line is that invasive species fundamentally alter ecosystems, causing issues for native species. 

At ARC, we combat invasives across the US in PARCAs, or Priority Amphibian and Reptile Conservation Areas, and thanks to an America the Beautiful Challenge grant from the National Fish and Wildlife Foundation, we are expanding that work across the country. If we can give native species their competitive edge back, they can thrive once again. 

Southwestern & Western PARCAs

Historically, the deserts of Arizona, Nevada, and southern California rarely if ever burned. There wasn’t enough vegetation for a fire to spread, and so the species of this landscape, including tortoises and Saguaro cacti, evolved without fire. Now, invasive grasses like buffelgrass have arrived from Africa, the Middle East, and Asia, and they are hardy enough to grow across the desert, providing fuel for when a fire starts. That means that plants and animals of the desert are suddenly facing an ecosystem with fire that, if it doesn’t kill them outright, alters the face of their home and the function of their ecosystem. In these areas, we are removing invasive grasses to try to stop fire across the landscape. 

We are also working to combat invasive species in freshwater ecosystems throughout the region, where three animals in particular—bullfrogs, sport fish like bass, and crayfish—have wreaked havoc. Invasive bullfrogs, introduced from the eastern US, are efficient top predators that eat everything in a wetland. Nonnative game fish eat smaller native fish that federally-listed threatened Mexican and narrow-headed garter snakes rely on. Invasive crayfish consume everything they can, even mowing down the vegetation, which causes run-off and erosion. 

To combat these species, we take relatively simple actions. For bullfrogs, we locate and remove egg masses and prevent their reproduction. For crayfish, we catch as many as we can and remove the gonads of the males—it sounds strange, but it’s the same solution as neutering stray cats. Then, we release the male crayfish back into the wetlands, and they mate with the females but can’t produce offspring. 

Southeastern PARCAs 

In the southeastern United States, invasive species cause different problems. In longleaf pine ecosystems, which house threatened and endangered amphibians and reptiles like the frosted flatwoods salamander and the gopher frog, invasive plants like autumn olive and privet grow in the wetlands where these species reproduce. They form such a thick, dense shrub ring that native plants can’t grow, including the grass species that the amphibians need to lay their eggs. Plus, the invasive plants are so thick that they absorb a great deal of water from the wetlands, even drying them up. 

Where possible, we remove these shrubs and help native plants reestablish a foothold. Prolific native grasses are also important for gopher tortoises; invasive grasses like cogongrass and Chinese silvergrass can outcompete native species, which serve as the tortoises’ food source, leaving them with limited resources. 

Invasive species aren’t a problem simply because they don’t belong somewhere—they are dangerous because they completely change the game for native species. And when there is a species, like the frosted flatwoods salamander or the Chiricahua leopard frog, that has adapted over millions of years specifically for a certain habitat, introducing a new player that evolved under completely different circumstances throws the whole ecosystem out of balance. At ARC, with your help, we want to restore that balance, and maintain our landscapes as the stunning networks that they are, with native species as their stars.