The question of whether rabbits are invasive does not have a simple yes or no answer, as it depends entirely on the species and the geographical location. While many native rabbit species, such as the North American cottontail, are a natural part of their ecosystems, one species in particular has achieved global notoriety as one of the world’s most destructive introduced mammals. The European rabbit, through a combination of biological traits and human introduction, has caused environmental and economic disruption across multiple continents. To understand the rabbit’s global impact, it is necessary to examine the precise definition of an invasive species and the history of its rapid colonization.
Understanding the Invasive Species Designation
To be designated as an invasive species, an organism must satisfy two distinct criteria: it must be non-native to the ecosystem under consideration, and its introduction must cause or be likely to cause economic or environmental harm. A species that is simply “non-native” or “exotic” may have a neutral or even beneficial effect and is not considered invasive. The European rabbit (Oryctolagus cuniculus) is primarily responsible for the global invasive pest designation, originating solely in the Iberian Peninsula and parts of North Africa.
This distinction is important because native species, such as North American cottontails or the snowshoe hare, are adapted to local predators and climate, and their populations are naturally regulated. While feral domestic rabbits (also Oryctolagus cuniculus) contribute to the problem, the massive damage is driven by established wild populations of the European rabbit when introduced outside its natural range.
The European Rabbit: A Global Case Study
The European rabbit’s success as a global invader is a textbook example of biological catastrophe. Although rabbits were introduced to Australia numerous times since 1788, these early releases were mostly domestic stock that failed to thrive. The true invasion began in 1859 when English settler Thomas Austin released approximately two dozen wild-type rabbits on his property in Victoria for hunting purposes. Genetic analysis traced the ancestry of the current massive population back to this single release, suggesting the wild ancestry carried a genetic advantage for survival.
This small group led to an explosion in population, spreading across the continent at a rate of up to 100 kilometers per year and colonizing most of the southern half of Australia within 50 years. This rapid colonization was facilitated by their high reproductive capacity, with a single female capable of producing 18 to 30 young per year. Extensive underground warrens provided protection from predators and the harsh climate, allowing them to rapidly establish themselves in diverse habitats. This pattern of introduction and ecological success was replicated in New Zealand, where the rabbit also became a serious pest.
Ecological and Agricultural Impacts
The sheer numbers and aggressive grazing habits of invasive rabbit populations lead to severe ecological and economic damage. Ecologically, rabbits are responsible for the decline of over 300 threatened Australian plant and animal species through competition and land degradation. Their intense grazing destroys native seedlings and grasses, preventing the regeneration of native flora and fundamentally altering entire landscapes.
The constant grazing and burrowing destabilize topsoil, leading to significant wind and water erosion, especially during drought periods. This soil loss degrades habitats and reduces water quality. Economically, the impact on agriculture is substantial, costing Australian agriculture more than $200 million in lost production annually. Rabbits compete directly with domestic livestock for pasture, with seven rabbits consuming the same amount of feed as one dry sheep. They also damage grain crops and intensive horticultural operations by feeding on newly planted vegetation, reducing yields.
Methods for Population Control
Mitigating the damage caused by invasive rabbits requires a sustained and integrated approach, utilizing a combination of biological and conventional control methods. Biological control, which uses viruses to reduce rabbit numbers at a landscape scale, has historically been the most cost-effective method. The Myxoma virus, introduced in Australia in 1950, initially caused mortality rates near 99.8%, though effectiveness declined as the rabbit population evolved genetic resistance.
The introduction of Rabbit Hemorrhagic Disease Virus (RHDV), a calicivirus, in 1996 and its subsequent variants, like RHDV2, provided a second wave of population suppression. RHDV has been highly effective in arid zones, although a benign endemic calicivirus sometimes confers partial immunity to lethal strains, necessitating ongoing research. Because biological agents are not a complete solution, they must be supplemented with conventional controls at the local level, including:
- Warren ripping (destroying the burrow systems)
- Fumigation
- Poison baiting
- Targeted shooting