Invasive and Non-Native Species

Many ecologists have acknowledged the problems caused by invasion of non-native species into communities or ecosystems and the associated negative effects on global patterns of biodiversity (Stohlgren et al. 1999). Once established, invasive species have the ability to displace native plant and animal species (including threatened and endangered species), disrupt nutrient and fire cycles, and alter the character of the community by enhancing additional invasions (Cox 1999, DeLoach et al. 2000, Zavaleta et al. 2001, Osborn et al. 2002).

Noxious weed infestation is now the second leading cause of native species being listed as threatened or endangered nationally. As of 1998, non-native species have been implicated in the decline of 42% of species federally listed under the Endangered Species Act (Center for Wildlife Law 1999). In addition to environmental problems, invasive plants also pose a serious economic problem. Rangelands infested with Russian knapweed, a serious problem in New Mexico, typically suffer reductions in livestock carrying capacity of 50% or more. The State Forest and Watershed Health Plan devotes significant planning to the management of non-native invasive phreatophytes (New Mexico Energy, Minerals, and Natural Resources Department 2004).

Non-native aquatic species have considerable affects on native fish, molluscs, and crustaceans in New Mexico's aquatic habitats. The integrity of native fauna populations is negatively affected by non-native species through resource competition, predation, hybridization, habitat alteration, and through the introduction of diseases and toxins.

Diseases, Parasites, and Pathogens
Many of the avian and mammalian SGCN are affected by diseases such as West Nile virus, rabies, hantavirus, pasturella pneumonia, and bubonic plague (Table 4-4). The growing wildland urban interface exposes wildlife to potentially infected domestic and feral pets and may contribute to the spread of these diseases. Increased exposure to refuse, pesticides or other toxins, and parasites may also affect wildlife at this interface.

The presence of whirling disease in rainbow trout (Oncorhynchus mykiss) was confirmed in New Mexico the spring of 1999. Since this confirmation, four of the six New Mexico state hatcheries, several private ponds and salmonid populations in the San Juan, Rio Grande, Canadian, and Pecos drainages in New Mexico have tested positive for the disease. As a result, routine testing and remediation procedures have begun in New Mexico's hatcheries and a testing program has been initiated for 173 coldwater streams and reservoirs. These waters may have been contaminated through inadvertent stocking of infected rainbow trout or by natural or anthropogenic vectors. Although New Mexico has adopted a "no tolerance" policy that bans the stocking or importation of fish infected with whirling disease, the potential for accidental introduction still exists. The most devastating potential of the disease lies in the threat it poses to native salmonid populations that rely on natural reproduction.

Rio Grande cutthroat trout (Oncorhynchus clarki virginalis) presently occupies a fraction of its presumed historic range throughout the Rio Grande watershed (Stumpff and Cooper 1996, Calamusso and Rinne 1999) and is considered at risk by the NMDGF (Paroz et al. 2002). Recent surveys indicate populations of Rio Grande cutthroat trout are reproducing in the Jemez and Pecos drainages (DuBey and Caldwell 2003). Portions of the Pecos drainage have tested positive for Myxobolus cerebralis (whirling disease causal agent) (Hansen 2002). Very little is known regarding whether the disease exists in cutthroat trout populations. However, the species produces young fish from March through June when temperatures are conducive for optimum triactinomyxon production. Thus, it is likely that if M. cerebralis were to spread to Core Conservation Areas for Rio Grande cutthroat trout, the species would be at risk of infection. Core Conservation Areas contain isolated populations of Rio Grande cutthroat trout and are specifically managed for their genetic purity and potential use in restoration of the species.

Chronic wasting disease is also a concern in New Mexico. A total of 12 cases of chronic wasting disease have been confirmed in New Mexico as of September 2005. All were mule deer (Odocoileus hemionus) located in the Organ Mountains east of Las Cruces. Two mule deer subjected to tonsillar biopsies and released in December of 2004 in southern New Mexico as part of a research project were later found to be positive for chronic wasting disease. In 2001, a New Mexico game park imported 21 elk from a southern Colorado game ranch at which animals tested positive for chronic wasting disease. Investigation revealed that, subsequent to the initial importation, the New Mexico facility transferred animals to four other game parks in New Mexico. All five New Mexico game parks are precluded from transferring ungulates until the imported animals are shown to be disease free for not less than 60 months. No New Mexico game parks have as yet tested positive for chronic wasting disease.

Phytophagous (plant-eating) insect outbreaks cause tree mortality and reduced growth in New Mexico's forests and woodlands (Haack and Byler 1993). Bark beetles and inner bark borers are primary tree killers (Haack and Byler 1993). Phytophagous insects have traditionally been considered detrimental to forest health and commercial timber harvest (Schowalter 1994). However, most phytophagous insects that affect forest trees in New Mexico are native organisms (Wilson and Tkacz 1994) and, from an ecosystem perspective, perform functions that are instrumental in sustaining forest health and function through succession, decomposition, nutrient cycling and soil fertility (Haack and Byler 1993).

Altered forest conditions have likely increased the frequency, intensity, and extent of insect outbreaks and diseases (Haack and Byler 1993, Wilson and Tkacz 1994, New Mexico Energy, Minerals, and Natural Resources Department 2004). Changes in forest tree age, size, density, species composition, and vertical stratification across temporal and spatial scales influence patterns of forest insect herbivory at the ecosystem and landscape levels (Schowalter et al. 1986, New Mexico Energy, Minerals, and Natural Resources Department 2004). Environmental stresses such as drought, late spring frosts, wind throw, and air pollution can encourage insect outbreaks (Haack and Byler 1993). Although insect outbreaks in forest ecosystems occur naturally, they can cause shifts in vegetative species composition and structure (Haack and Byler 1993). Further, certain phytophagous insects are attracted to fire-damaged or fire-killed trees and their build-up in weakened host trees can threaten adjacent, unburned stands (US Forest Service 1999).

The magnitude of disturbance from an outbreak depends upon the particular insect or pathogen, and on the condition of the forest ecosystem affected (Wilson and Tkacz 1994). Closely spaced host trees are likely to trigger outbreaks of phytophagous insects and pathogens. In compositionally and structurally diverse forests, however, potential host trees can be harder for insects to locate among non-host trees, and vulnerable host trees may be relatively resistant to small numbers of insects that find their way through the surrounding non-host vegetation (Hunter and Aarssen 1988, Waring and Pitman 1983). Outbreaks are typically worse in single-species, monocultural tree stands especially during vulnerable periods such as drought (Mattson and Haack 1987, Schowalter and Turchin 1993, Waring and Pitman 1983). Populations of most foliar and sap-feeding insects peak during particular stages of host-tree development (Schowalter et al. 1986), which make monoculture stands of single-aged trees more susceptible to outbreaks.

Drought provides a more favorable environment for phytophagous insect growth, survival, and reproduction, and may reduce the effectiveness of the biochemical defense system that some plant species have evolved (Mattson and Haack 1987).

Table 4-4

Table 4-4. Potential diseases, hazards, toxins, and parasites contacted by wildlife at the wildland-urban interfaces.

Potential Diseases, Hazards, Toxins, and Parasites Avifauna Mammals
Rabies X
Bubonic plague X
Canine distemper X
Electrocution X X
Tuberculosis X
Foot and mouth disease X
Contagious ecthyma X
Pesticide poisoning X X
Lead poisoning X X
Gastroenteritis (clostridials) X
Bovine diarrheal virus X
Lungworm and pneumonia complex X
Tapeworm larvae/hydatid cysts X
Ear mites X
Brucellosis (currently in Wyoming and Montana) X
Vesicular stomatitis X
Canine heartworm X
Parvovirus X
Tularemia X
Feline panleukopenia (feline leukemia) X
Salmonella X X
Giardia X
Chronic wasting disease X
Johne’s disease X
Bluetongue and hemorrhagic disease X
Mycoplasma diseases (sinusitis) X
Pasturella (avian cholera) X
West Nile disease X
Blackhead disease X
Avian pox X
Trichomoniasis X
Avian influenza X