Invasive Species

General Facts


Cats--feral cats feed mostly on black rats, but native birds, iguanas, tortoises, insects, crabs, and lizards are also a part of their diet (Perry 1984). They are also a definite and primary host of toxoplasmosis, a disease caused by the parasitic protozoan Toxoplasma gondii (Cox 2004).
    The parasite reproduces within the intestinal tracts of cats and is found in cat feces. The parasite can remain active in soil for up to ten years.  Humans become infected by eating raw or badly cooked meat. The protozoan invades the central nervous system, skeletal muscles, lymphatic tissue, the eyes, and other organs. From there, it undergoes asexual replication, causing cell death and inflammation to the host (Kasper 2000). It causes flu-like symptoms, but in extreme cases permanent eye or brain damage results. Infected fetuses can be born retarded (Phillips et al. 2003). About 33% of all pregnant women infected will pass the disease onto the fetus. The best way of preventing toxoplasmosis is to wash all foods before eating, avoid uncooked meat, and to wash your hands after cleaning a litter box or working with soil (Kasper 2000).

Dogs--feral dogs are a major problem on the islands. They will eat both tortoise eggs and young tortoises. Other parts of their diet consist of penguins, marine iguanas, lizards, and birds, including the dark-rumped petrel and possibly the endangered Galapagos hawk (Thornton 1971). In the 1970's, a group of wild dogs killed over 500 land iguanas in an attack, and left the bodies to rot (Perry 1984). The domestic dogs who live on the islands will sometimes play with the marine iguanas for fun, and end up injuring or killing them. Through intensive poisoning and shooting programs, feral dogs are no longer present on Floreana.
Solutions.
   
Pigs--pigs will eat ground nestling birds, insect larvae, and the eggs of lizards, snakes, turtles, and tortoises. They destroy tortoise nests and eat the hatchlings (Thornton 1971). Sometimes, a pig will snatch an egg from a tortoise or turtle as it is being laid. On some beaches, the pigs will dig up every single egg. This can be seen every year on the beaches of Santiago, southern Isabela and Santa Cruz, where green turtles (Chelonia mydas) lay their eggs (Perry 1984). As a result, sea turtle hatching rates have gone from 80% to 3%. It is possible for just 2 pigs to destroy 23 tortoise nests within a month. Feral pigs uproot plants and can carry infectious diseases. On Santiago island, the pigs are covered in jigger fleas (Tunca penetrans), which infect humans as well (Perry 1984). Pigs not only destroy the burrows of dark-rumped petrels; they eat both hatchlings and adults. In some instances, pig fat was so contaminated with the smell and taste of the bird that the meat was inedible (Harris 1970).
Solutions.

Goats--viewed by many as the single most damaging invasive species, goats will eat every leaf off the plant they consume. Goats are polygamous, so goat populations increase very quickly.  Goats wipe out the native vegetation, increase soil erosion, and compete with tortoises, land iguanas, and native birds for food (Thornton 1971). Due to the presence of goats, the Galapagos tomato plant, and the wild cotton, are both extinct.They are now gone from Floreana, due to hunting and poisoning programs.
Solutions.

Horses--horses compete with adult tortoises for fresh water resources and pasture space. They also trample the nests and burrows of native species (Perry 1984).

Donkeys--they trample tortoise shells, step on tortoise nests, and increase soil erosion through eating and trampling the local vegetation (Perry 1984).

Cattle--they trample native vegetation and destroy tortoise nests and iguana burrows by stepping on or rolling over them (Thornton 1971).

Frogs (Scinax quinquefasciata)--there are now a few frogs living in saline coastal lagoons (Charles Darwin Foundation Annual Report 2003). They are a very recent invasive species, arriving by cargo boat in Puerto Villamil (Isabela Island) in 1998. Their populations have increased since March 6, 2002, after 3 days of rain that left 341 ml of water on the island. After that, frog sightings were reported in the streets of Puerto Villamil, meaning their range has expanded into urban zones. In addition, kikuyo (Pennisetum clandestinum), an introduced plant, provides a good habitat for frog eggs and tadpoles (Update from CDF News Room 2002).
Solutions.

Rock doves--they used to live on four of the five inhabited islands (Santa Cruz, Isabela, San Cristobal, and Floreana, but not Baltra). The owner of the Floreana flock abandoned the birds in the 1980's, and as a result the birds died or moved onto other islands (Phillips et al. 2003).

Black rat (Rattus rattus)--black rats are so competitive that no native rodents survive on the Galapagos Islands  where they are present, except for Santiago (Still et al. 2000). Research shows that the endemic rice rats on Santiago (Nesoryzomys swarthi) eat cactus plants and fruits, while black rats do not. This would explain how they have survived competition with black rats. However, this is something to consider when trying to reintroduce rice rats onto islands where there are no cactus plants (Charles Darwin Foundation Annual Report 2003). Omnivorous and agile, black rats often climb trees in search of food. Parts of their diet include tortoise hatchlings and eggs, and dark-rumped petrels (Thornton 1971). According to Harris (1970), upon visiting the nests of dark-rumped petrels, he noticed rat droppings "in every hole and cranny."
    They are also capable of rapid evolutionary adjustments--this is most noticeable on isolated oceanic islands. For example, the rats tend to be smaller on islands where the house mouse and the kiore are also present. Thus, black rats are bigger when not surrounded by similar species that they must compete with. A larger body size gives them a further advantage over their prey (Cox 2004). On average, 83% of their diet comes from plants, but younger rats eat about 30% animal  material, while mature rats each less than 20% animal matter. The giant tortoises of Isla Pinzon (to the northwest of Santiago Island) have been greatly affected by black rats. In a period of 10 years (in the 1960's and 70's), 7,000 to 19,000 hatchlings were born, but only a single one-year old tortoise was found on the entire island (Perry 1984).
 Solutions.

House mouse (Mus musculus)--it has a global range more extensive than any mammal except for humans. They destroy crops and breed very quickly, sometimes reaching plague-like populations. Females can breed at just 5 weeks, and with the right conditions, the population density can reach 200,000 mice per ha. They will eat roots, leaves, insects, and human foods. Their phenotypic plasticity and the speed of population growth allows them to adapt easily to new environments. In addition, they are host to diseases such as the bubonic plague (Yersinia pestis) and salmonella, even though they rarely transmit such diseases to humans.
Solutions.

Little fire ants (Wasmannia auropunctata)--introduced around 1910 or 1920, they kill other arthropods, snails, and beetles. They will feed on turtle hatchlings and blind adult turtles. In addition, their powerful sting irritates humans. This species does not depend on a single queen to establish a new colony. Instead, fire ants live in a series of underground colonies (located below leaf litter, rocks, and soil) connected by complex tunnels. Every colony has several queens, workers, and young ants in various stages of development. The population will radiate outward from the point of origin. One study on Marchena showed them spreading from 2 ha to 18 ha between 1996 and 1998. A possible explanation for the rapid rate of spreading is El Nino, which brings higher precipitation rates (Roque-Albelo et al. 1999). Solutions.

Tropical fire ants (Solenopsis geminata)--introduced around the same time as the little fire ant, the tropical fire ant lives on the soil surface. They eat invertebrates and possibly disrupt tortoise, penguin, and land iguana nesting habits. Winged females can fly over large distances to start a new colony (this is called colony budding). The formation of far-scattered colonies makes the fire ant difficult to control. When members of the Charles Darwin Foundation visited the Marielas islets (to the West of Isabella island), the fire ant population was so high that some activities on the islets had to be cancelled. Black rats caught in traps have been found dead and surrounded by fire ants, which was the possible cause of death (Roque-Albelo et al. 1999). Polygyny (more than one reproductive queen per colony) gives these ants a high population growth rate (Tsutsui 2003).

Black fly--probably introduced through a shipment of bananas from Ecuador. They transmit river blindness, as well as Leucocytozoon, a parasite of white blood cells that attacks birds. They feed on vertebrae blood, and will bite humans, leaving large, painful welts and an intense itch. Some farmers on San Cristobal have abandoned their homes due to the black fly. The larvae live in freshwater streams, and over time may displace the native invertebrates (Roque-Albelo et al. 1999). Solutions.

Wasps (Polistes versicolor)--probably introduced through a shipment of bananas. They spread over large areas by flying, or are taken around the islands by cargo and tourist ships. They are more commonly found during the dry season, around coastal areas, and that is also when they are more aggressive. Nests form from a single gravid female (a female carrying eggs or young) (Roque-Albelo et al. 1999). In a study done by Grant et al. (1997), dozens of these wasps were observed flying around mangrove flowers and dead wood. If they eat beetle or bee larvae, a main food source for the endangered mangrove finch, they will decrease the finch population.

    Of the introduced plants, 75% were first brought for cultivation. 42% of those now thrive in the wild without human aid. Since the 1980's, both human and invasive species populations have grown exponentially. Even more damaging are the fungi and soil invertebrates present in the seeds and in the invasive plants themselves. However, there is a lack of synthesized data on these species (Mauchamp 1997).

Psidium guajava (guava plant)--first introduced in 1870, they look like shrubs or small wide-spreading trees. This plant has taken over much of the terrain, forming extensive forests, and edging out the native evergreen forests, composed of many endemic flora. The introduced cattle on the islands create open spaces for further germination by grazing. When cows eat the fruit, they excrete the seeds, which grow better in cow dung. The seeds also stick to the hooves of pigs and cattle; in moving around the islands, they help to disperse the seeds over a larger area (Thornton 1971). Increased fire frequency actually helps the guava to grow, since they regenerate quickly compared to endemic plants.
Solutions. 

Guava plant picture

Scott Henderson @ USDA-NRCS PLANTS Database


Lantana camara (a shrub)--they take root in places where dark-rumped petrels like to make their nests. This shrub also impedes birds' routes in and out of their burrows. They regenerate easily; when one stalk is cut away, three or four may grow in its place (Perry 1984).  Dry soil and cold temperatures impede their growth (Hannan et al. 1998). Birds disperse it because of its small black fruits, and gardeners increase their spread by planting them for their attractive flowers. Research done by the CDF shows Puccinea lantanae (a fungus) to be a possible future biological control of the shrub. This fungus was isolated from Lantana camara living in Peru. When tested, the fungi attacked the Lantana camara of the Galapagos, causing its shoots to die and its leaves to fall off. The fungus did not affect Lantana peduncularis, which is endemic to the Galapagos Islands. Before plans are discussed to release this fungus onto the islands, additional research will be required to see its effect on other endemic species. It is estimated that this will take about two years.
Solutions.

lantana camara
Photo by Agnes Rinehart, http://www.hear.org/pier/imagepages/singles/lacamp1.htm


Solutions: an Overview

    It is often impossible to completely eradicate a problem species, due to cost and undesirable damages. Instead, maintenance management is utilized, where the population is kept low enough so it can be tolerated in the environment. One example is the United States' attempt to eradicated the fire ant. Over $200 million was spent, and in the end many of the ants' natural predators were killed, therefore possibly increasing the fire ant population (Simberloff 2002).
    In the Galapagos, tourists' luggage are checked upon arrival, but it is usually done quickly, and not very effective in screening out invasives. Plant seeds can arrive attached to the wheels of planes or the bottoms of shoes. There have been suggestions that all ships should be fumigated to prevent the introduction of new insects (Jackson 1993).
    In 2000, the Galapagos inspection and quarantine system (SICGAL) was initiated. It is managed by the Ecuadorian Agricultural and Health Service (SESA), and aims to prevent further invasive species from entering the islands. CDF-trained inspectors work on the four inhabited islands (Floreana, Santa Cruz, San Cristobal, and Isabela), checking bags and performing long-time surveillance. So far, they have

    Current solutions
        Cats and dogs--a new organization, called Animal Balance, has started using injections to sterilize the local cats and dogs. During last April and May, the veterinarians and volunteers who work for the program sterilized (using a combination of surgery and Neutersol® injections) about 80 cats and 240 dogs (many of which were domestic, due to the difficulty in trapping the feral animals) on Isabela Island. The injection allows male dogs to keep their testosterone levels at 50%. This way, the dogs can still hunt or guard, which is what domestic dogs on the islands are usually used for. Animal Balance hopes to expand the program to other islands in the Galapagos, and plans to return there in December 2004.
            Here are the pros of Neutersol®, from http://www.animalbalance.org and http://www.neutersol.com/About%20Neutersol.htm
                --FDA approved
                --over 99% effective
                --permanently sterilizes dogs without surgery
                --no general anesthesia needed
                --the injection takes less time than surgery
            Here are the cons of Neutersol®, from http://www.friendsofanimals.org/04win/neutersol.html and http://www.neutersol.com/About%20Neutersol.htm
                --the drug was over 20 years in the making, and was tested on hundreds of dogs before becoming FDA approved
                --there is evidence that the lab animals used were killed a year after they first received the injection. Side effects tested for include vomiting, continuous                          barking, hyperactivity, and tail-biting
                --the injection only works on male puppies between 3 and 10 months old
                --possible side effects include pain and testicular swelling, vomiting, loss of appetite, and lethargy
                --the drug is not 100% effective immediately, and newly injected dogs should be kept away from female dogs in heat for at least 60 days

        Pigs--usually, poison is used, along with hunting by dogs, but pigs are surprisingly intelligent. In addition, pigs reproduce quickly, and are crepuscular or nocturnal, making it even harder for humans to deal with them (Perry 1984). In Hawaii, snaring has been used in fenced areas. However, many cultures value pigs as a food source, and the reasons for eradication must be made clear before a plan is put into action.

    Goats--large-scale solutions were carried out by people shooting at goats from helicopters. On Barrington, natives opposed the eradication plans because they wanted to keep the goats as a source of continuous fresh meat, even though goat hunting occurred only rarely. A compromise was finally reached where the natives were encouraged to shoot the females, which would help reduce goat populations. Shooting at males is useless, since goats are polygamous.

        Frogs--the Charles Darwin Foundation (Annual Report 2003) tested for the salinity tolerance of frogs, and found that they could not survive in water with more than 14% salt content. This raises the possibility of pumping seawater into lagoons to raise the salinity, therefore killing the frogs.

        Black rats (Rattus rattus)--they can be eradicated from small areas by using rat poison. The type of poison generally used is called "second-generation" anticoagulant poisons. However, this kind of poison also harms non-target species and causes secondary poisoning of cats that eat the rats. It's also possible that the rats will develop a resistance to the poison. The only case in the Galapagos where black rats were successfully eradicated occured in Bartolome, a small island off the coast of Santiago. This was done through intensive trapping and poisoning programs (Perry 1984).

        House mouse (Mus musculus)--in general, the population can reduced by using traps, poisons, cats, pesticides, and by fumigation.

        Little fire ant (Wasmannia auropunctata)--the little fire ant has been eradicated from Santa Fe island, due to clearing of vegetation, fires, and non-selective ant poison. It is believed that eradication is more feasible on smaller islands or more isolated places where the population is spread over no larger than a few dozen hectares. The Charles Darwin Foundation is trying to secure funds to eradicate the fire ant from Marchena, another small island.

        Black fly--it will be difficult to eradicate them, as the larval stages live in fresh water, and fresh water sources are hard to find on the islands. The Charles Darwin Foundation is collecting water samples from rivers in San Cristobal, to test for the presence of Bacillus thuringiensis israelensis, a bacteria that could be used as a biological control for the black flies.

        Psidium guajava--the key is to restrict cattle movement. Existing trees are being cut, and their stumps painted with herbicide.

        Lantana camara--a recent discovery, consisting of cutting and selective herbicide application, shows promise. The Charles Darwin Foundation is currently running a trial method for the control of this plant, called "basal bark." Oil-based herbicides (at concentrated levels) are sprayed onto the bottom (the lowest 12-18 inches) of the plant stem (Botany Department, CDF 2003). Burning is used in open pastures, and large-scale herbicide applications are not very feasible in the Galapagos where it will affect other organisms. The most effective herbicides are called "growth hormone" herbicides, and they impede cell growth. Examples include the benzoic acid group (dicamba) and the pyridine group herbicides. Herbicides aimed at preventing photosynthesis ( the triazine, uracil, and urea groups) were the least effective (Hannon et al. 1998).


General Facts and Characteristics of Invasive Species

The following information is taken from Cox (2004).

Invasives are almost invariably preadapted for dispersal into new areas. These adaptations include natural, evolved characteristics such as
·    spores, seeds, and larval stages that can easily be carried by wind or water. In these stages the organism can survive for long periods of time before reaching a new region where they can grow and reproduce. Plant pathogen spores such as rusts or other types of fungi can be carried across oceans
·    duckweeds, and floating plants in general, can break into multiple sections. These parts are carried by currents to new places, where they grow into the entire plant and multiply
·    plants and weeds with burrs, hooks, or awns get tangled up in animal fur, and are thus taken to wherever the animal goes
However, these techniques are most effective within an island or across continental areas. Dispersal across major oceans involves human aid.
·    seeds stick to, and are carried by, all types of vehicles including planes, trucks, and cargo ships. Ballast water has introduced about 35 species of fish to new regions in the world
·    crop seed contaminants are shipped all over the world 
·    insects will go wherever shipments of food are imported

Cropland weeds that have evolved to have seeds and growth patterns similar to those of crop plants are called agroecotypes. In some cases the weed seeds are harvested with the crop seeds, and subsequently planted and carried to new regions. One example of crop mimicry is vetch (Vicia sativa), with flat seeds that mimic lentil (Lens esculenta) seeds.

Humans have deliberately introduced new species into regions for the following reasons:
·    agricultural, ornamental,  medicinal, or herbal
·    trees are introduced for timber and fuel, or to serve as windbreaks
·    domestic animals are introduced as livestock
·    game fish
·    invertebrates are introduced for aquaculture or display aquariums

Upon reaching a new region, invasive species need to establish a stable population. These characteristics allow them to do that:
·    alien weeds can self-fertilize and are apomictic (meaning they can produce seeds without fertilization)
·    small seed size, which means smaller DNA content, smaller cell volume, and higher seed number. These seeds are lighter and better adapted for dispersal; they also have shorter generation time and higher germination rates
·    many of the most successful invasive animals eat a variety of foods, adapt easily to physical conditions, are r-selected species (small body size, short lives, large number of individuals born at a time), and exhibit type III survivorship curves

Oceanic islands, many of which lack large land herbivores or predators, are particularly susceptible to alien plants. Alien plants make up 20% to over 80% of the flora on many oceanic islands. The enemy release hypothesis states that by invading lands far away from their original habitat, plants leave behind the main herbivores that used to feed on them. It will take time before the herbivores of the new habitat will begin to feed on the alien plants, so in the meantime the invasive plants will multiply under minimal stress. A study showed that purple loosestrife, native to Europe, grew taller and had more biomass than those living in Europe. Phenolic compounds, which are used to repel herbivores, existed in lower concentrations in North American loosestrife.


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