Invasive versus exotic species: Know the difference?
These days, the terms invasive species, exotic species and invasive exotic species are used commonly when referring to flora and fauna invading natural and disturbed habitats.
Many people think that the words “invasive” and “exotic” are synonymous when in fact they are very different. Exotic simply means non-indigenous to an area, which is the opposite of native which means indigenous to an area. Invasive means tending to spread prolifically and undesirably/harmfully.
“A common misconception is that only exotic species can be invasive. Native species can also be invasive in natural habitats if environmental factors are changed,” Sanibel-Captiva Conservation Foundation Wildlife & Habitat Management Director Chris Lechowicz said.
For example, the addition of excess nitrogen and phosphorus into a wetland from nearby herbicide/pesticide use or runoff from cattle farms results in cattails dominating the habitat. On Sanibel, cabbage palms, a native species, are considered invasive in several habitats due their tendency to form monocultures if the natural fire regimes are not followed.
“There are many areas where cabbage palms are so dense, it is difficult to walk through the infestation. This is both unnatural and a substantial wildfire risk as fire could easily and quickly travel through the canopy of overlapping fronds where it would be difficult to stop, if needed,” Lechowicz said.
Historically, palms trees and many other plant species were kept in check by periodic fires. The land management team at the SCCF strives to preserve various habitat types for the wildlife that needs those habitats to survive. That involves various methods to mimic the natural cycle such as burning, mowing, thinning, and chemical treatments of both native and non-native plants.
“Both native and exotic invasive plant infestations take up the bulk of our time,” he added.
The most obvious invasive exotic plants on Sanibel are the Brazilian pepper, Australian pine and air potato. These are both non-indigenous to our area and highly aggressive at infiltrating landscapes. Intensive efforts are taken to keep densities of these plants low. Annual treatments of the same areas are required to rid the area of new sprouts from seeds in the ground.
Highly invasive and exotic animals such as the Cuban treefrog and the Cuban brown anole are very common on the island and appear like they have always been a part of the native ecosystems.
“Both species arrived here decades ago on vessels, cargo and plants that were brought to the island,” Lechowicz said. “With a low diversity of native species on the island and ample habitats and space, these animals flourished and spread throughout the island becoming some of the most abundant species.”
The larger size, more aggressive nature, or the absence of a similar native species in the habitat resulted in these invasive exotic species to become the dominant species in many areas. Some such as the greenhouse frog and tropical house gecko have minimal, if any, impact on native species.