Invasive exotic species and climate change

With climate change come changes in species distributions. Invasive exotic species in particular can have significant effects upon other species and the structure and function of entire ecosystems.

Background

An exotic species is a creature found in an area to which it is not native. Species that succeed after arriving in new areas, whose population growth is not limited by natural controls, and that negatively affect other species in their new ecosystems are considered invasive exotics. Such species often evince preadaptations for surviving differences in climate, so increases the threat they pose of rapidly invading new ecosystems.

Many exotic plants can only exist in new areas with special care and conditions, such as soil fortified with nutrients, a special watering regime, artificial lighting, or protection from cold. Many landscape plants, agricultural plants, domesticated livestock, and pets are exotic plants or animals that benefit humans when brought to new areas. Invasive exotic species spread uncontrollably and become problems for native species and humans. Often, their invasive potential is not apparent until long after they have become established in a new niche.

Exotics and Global Warming

Global warming is one aspect of the more complex phenomenon of global climate change, and the bigger picture of climate change must be kept in mind relative to invasive exotics. Among other attributes, global climate change can include changes in temperature ranges; timing and amount of precipitation; wind patterns; frequency and intensity of storms; and frequency, intensity, and timing of lightning-started fires. Such changes can dramatically influence living creatures and favor invasive exotics.

Invasive exotic species are often adapted to be effective travelers and colonizers. Many plants can travel on animals, using hooked spines or sticky hairs that allow them or their seeds to adhere to clothes or fur. Lizards and insects may readily enter small openings in packing crates or suitcases and are inadvertently taken to new places. Other plants and animals can be dispersed over great distances by wind. Seeds often survive in the digestive tracts of animals that consume their fruit and are thus dispersed to distant locales. Wood pallets and goods, necklaces made with exotic seeds, and handicrafts made from palm leaves can contain insects and other plant pests or diseases that emerge after arrival at a new place.

Most creatures on the move do not survive the trip. Where they land is unpredictable, and most die, unable to cope with their new environment. They may be unable to reproduce for lack of a mate or appropriate breeding conditions. Those that survive are often adaptable and reproduce rapidly.

Biodiversity and Interspecies Relationships

Biodiversity is a result of adaptations to local conditions that hone the survival potential of each species. An ecosystem includes a community of living organisms interacting with their physical environment. The species fill unique niches, together fitting into the ecosystem like a hand fits into a glove. Each finger represents a species, and each has a defined space and role within the ecosystem. In a stable ecosystem, species work together smoothly. When a new species is introduced, it is like trying to fit a sixth finger into a five-fingered glove. The exotic species may displace a native species and take its place within the glove, or it may constrict the population of native species so that it carves out a new space within the glove. It may alter the glove in such a way as to form a suitable place in which to exist. These habitat alterations may affect the survival of native species and the ability of the ecosystem to function appropriately. Adaptation to specific conditions is beneficial only so long as those conditions prevail. Changes in the physical environment or in the species composition of an ecosystem can cause minor to major disruptions.

Global climate change reshuffles the deck of biodiversity, and new winners and losers are likely to emerge. Some species hold better cards than others: They are preadapted to specific changes in their ecosystems. Exotic species are often among those; they have already overcome numerous obstacles to establish themselves in their new habitat. Native species, especially specialists with specific adaptations to an existing environment, are often unable to adapt to changed conditions.

Why Exotics Become Invasive

When exotic plants and animals move or are moved from their native habitat to a new area, they often leave competitors, predators, and diseases behind, allowing their populations to grow unimpeded. If a species produces many offspring and has an easy means of dispersing, its population can grow rapidly, displacing, disrupting, or eliminating other species. In such circumstances, it has become invasive. Native species can become invasive also, but only if changing conditions or human impacts eliminate their natural controls. Invasive exotic species are found everywhere in the world.

Prognosis

The melting pots of Florida, California, and Hawaii are experiencing severe problems from exotic invasives. They have subtropical climates that favor introduction of exotic plants and animals. Although often for local use, many such plants are also farmed for markets in more northern areas, where they might only survive indoors as pets, houseplants, or outdoor perennial plants. Through the pet trade, many species of tropical fish, lizards, and parrots are breeding in Florida.

Interactions among exotics often exacerbate their effects upon an ecosystem, as introduced plants provide important food sources for introduced animals. In Florida, consumption of ornamental plants by exotic green iguanas (Iguana iguana), of plants and small animals by black spiny-tailed iguanas (Ctenosaura similis), and of animals as large as small dogs and cats by two-meter-long Nile monitors (Varanus niloticus) are regional problems that could spread northward with global warming. So, too, could the Burmese python (Python molurus bivittatus)—at up to six meters long and weighing ninety kilograms, one of the largest snakes in the world. It has been estimated that this snake could survive in the wild as far north as Washington, DC. It presently breeds in the Everglades ecosystem, where more than two hundred have been captured. Sources for this population include pets lost or released by owners, and some whose escapes were facilitated by hurricane-related damage.

Exotic plants once treasured for their blossoms or other attributes have invaded areas throughout North America and have the potential to spread farther north as the climate warms. Purple loosestrife (Lythrum salicaria), a native of Eurasia and widespread as an ornamental, replaces native plants and reduces habitat quality for wildlife as it forms dense stands in wetlands across North America. The Australian paperbark tree (Melaleuca quinquefolia) and Brazilian pepper (Schinus terebinthefolius), originally introduced as ornamentals, have formed dense monocultures in what had been habitats to a diversity of native plants and animals in south Florida. They are poised to spread northward as the climate warms. Kudzu (Pueraria lobata) vines, introduced from Asia to Gulf coast states in the 1800s to control erosion, often blanket ground, shrubs, and trees and are already expanding northward, following mild winters.

Major invasions of marine environments are also occurring around the world, as marine life is transported in the ballast water of ships. These invasions will alter natural ecosystems even further, as global climate change alters the temperature and of the oceans, creating new opportunities for invaders.

Context

As ecosystems are altered as a result of global climate change and enhanced invasions of exotic plants and animals, dramatic shifts in the populations of native species will result, causing the extinction of many species that are unable to compete favorably with their new neighbors. Shifts in ranges will vary from species to species, depending on their dispersal abilities, breeding success, and a diversity of habitat needs. A warmer climate might favor extinction of cold-adapted species and northward shifts for southern species, but if favored food plants do not shift at the same time or if a new range includes a predator or disease not previously encountered, the move could mean extinction.

Key Concepts

• exotic species: a species found in an area where it is not native
• habitat: an area normally inhabited by a particular species
• invasive species: a species whose population grows out of control and negatively affects other species
• niche: the role of a species within its ecosystem
• preadaptation: the ability of a species to move into a new ecosystem or to assume a new niche as a result of adaptations it already possesses

Bibliography

British Ecological Society. "How Climate Change and Invasive Species Threaten Tree Frogs." Science X, 16 Mar. 2023, phys.org/news/2023-03-climate-invasive-species-threaten-tree.html/. Accessed 15 Dec. 2024.

Cox, George W. Alien Species and Evolution: The Evolutionary Ecology of Exotic Plants, Animals, Microbes, and Interacting Native Species. Washington, D.C.: Island Press, 2004.

"Invasive Species Threaten the Success of Climate Adaptation Efforts." Invasive Species Advisory Committee (ISAC), US Dept. of the Interior, 14 Nov. 2023, www.doi.gov/sites/default/files/documents/2024-02/isac-climate-change-white-paper-november-2023.pdf. Accessed 15 Dec. 2024.

Occhipinti-Ambrogi, A. “Global Change and Marine Communities: Alien Species and Climate Change.” Marine Pollution Bulletin 55 (2007): 342-352.

Willis, K. J., and H. J. B. Birks. “What Is Natural? The Need for a Long-Term Perspective in Biodiversity Conservation.” Science 314 (November 24, 2006): 1261-1265.