How to Save Frogs from Extinction
The International Union for the Conservation of Nature (IUCN) Red List is a comprehensive list of animals and plants threatened globally. According to the IUCN Red List, 31% of surveyed reptile species are threatened or extinct and 32% or surveyed amphibians are either threatened or extinct with 42% in decline. It is important to note that these figures are for species that have been surveyed. There are many more species (especially amphibian) that have not been surveyed and sould therefore be going extinct without our knowledge.
There are many factors that can contribute to the decline in reptile and amphibian species worldwide. These include:
- Habitat change
- Pollution – especially water pollution
- Spread of disease
- Competing land uses
- Illegal and legal trade in species
The major factor impacting all reptile and amphibian species across the world is habitat change. This can take three forms, it can be the
- loss of habitat,
- habitat fragmentation and
- habitat degradation
Habitat loss and degradation have affected nearly 4000 species of amphibian worldwide. This is more than four times greater than the effect of pollution on species.
Habitat loss is the total removal of habitat due to land clearing generally for urbanisation or agriculture. It is most obvious and devastating form of habitat change that affects reptiles and amphibians. These animals have evolved specialised adaptations to exist in specific habitat types. Once a habitat is removed, the animals will no longer occur in an area. However, the effect of habitat loss is not restricted to the area that has been removed. Research in the US found that habitat loss due to urbanisation has contributed to the decline of the Red-Legged Frog (Rana draytonii) of California.
Habitat degradation is the reduced quality of land due to human impacts, such as selective clearing, pollution and neighbouring agricultural activities. Habitat connectivity is extremely important for the long-term survival of many species.
"Edge effect" is a term used to describe what occurs with regard to vegetation and wildlife when one type of vegetation shares a border with another. They may occur naturally (eg. forest grading into woodland, or stream side vegetation to drier nearby slopes, and burnt and un-burnt areas); or they can be man made, such as pasture abutting forest, or roads through forest. Some edge effects can be positive in terms of native flora and fauna, but most tend to have negative effects. Edge effects are most likely to have an influence on narrow strips or small remnant areas. In terms of corridor plantings, the wider the corridor the less impact of "edge effects".
Edges of habitats are susceptible to:
- Micro climate changes - solar radiation, air and soil temperature, wind speed, humidity levels can all be altered leading to stresses on existing vegetation, and change in types of plant seeds germinating.
- Change in wildlife species - as vegetation patterns change near edges, so usually do the types of wildlife that inhabit those areas. Edges can be important for some species, providing shelter, nest sites, perching and observation points (eg. parrots feeding on grass and grain seed, eagles on rabbits, grazing animals on grasses). Species with wider tolerances take over near edges and less tolerant species only survive in "core" areas away from edges. In narrow corridors or small remnant patches these 'core' species are generally absent. Aggressive edge dwelling species may invade and displace former inhabitants.
- An increase in pest animals - foxes, cats and dogs tend to move along and hide out near roads, tracks and cleared areas.
- Weed invasion - invasive plants can readily move into remnant vegetation and corridor plantings from adjacent agricultural, industrial or residential areas.
- Impacts from adjacent land use such as: chemical and fertiliser drift; erosion; trampling and grazing by stock; littering (eg. roadsides); altering water runoff characteristics (eg. drains).
- Noise and movement - many animals require quiet to breed and feed.
Generally, the longer the edge, the larger area is disturbed. Angular edges create greater edge effects, with sharp corners increasing disturbance. Smaller areas are at greater risk of impacts.
However, for some species, edges can create an ecotone which has its own micro climate that suits their needs at particular times of the year. For example, in Costa Rica researchers have been studying two species of Anoline Lizard along the edges and within the interior of a forest fragment surrounded by farmland. Interestingly, the lizards tended to use the edges during the drier months but moved into the interior of the remnant during the wet season.
There are various forms of pollution that can negatively impact reptiles and amphibians. The two main types are:
- Chemical Pollution – these can include acid rain, pesticides and endocrine disrupting chemicals (EDC)
- Nutrient Loading – excess nutrients can be extremely harmful to amphibians. The increase in algal blooms caused by nutrient loading reduces the amount of available oxygen for tadpoles and alters the invertebrate populations in these waterways.
Frogs and salamanders are sensitive to water pollution and this is believed to be the main reason for the dramatic reduction in frog population numbers worldwide. As frog eggs are not protected by a shell and tadpoles live in the water they are directly exposed to aquatic pollutants. These pollutants can affect development, causing abnormalities and at toxic levels can lead to death.
Environmental Acidification (Acid Rain)
The incidence of acid rain has decreased with the introduction of clean air legislation in many European countries and the United States. However, it is still a milder problem in these countries and a major problem in countries such as China and India. Acid rain is caused by the combustion of fossil fuels. It is the release of sulphur and nitrogen oxides into the air. These then react with the moisture in the air to create acid rain.
Acid rain causes the greatest problem for reptiles and amphibians where it falls on hard rock and soils that are low in minerals as these can not neutralize the acids. Aquatic amphibians are highly susceptible to the toxic effects of acid rain. Most amphibian species require low acidity water. Eggs also have a higher mortality rate of greater than 50% in acidic water.
Pesticides transported through the air, soil and waterways can have devastating effects on reptile and amphibian populations. Pesticides can cause physiological and biochemical changes in freshwater organisms by influencing enzyme activities. In the United States geological surveys showed that some pesticides carried across large areas on prevailing summer winds affected populations of amphibians breeding in mountain ponds and streams. Pesticides used to control rabbit populations in New Zealand are thought to have contributed to the decline in Giant Skink populations, either through primary or secondary (eating infected insects) poisoning.
Endocrine Disrupting Chemicals
EDC’s are substances that alter the hormonal and homeostatic systems that enable animals to interact with their environment. EDC’s can build up in turtle eggs, reducing shell thickness and therefore leading to reproductive failure.
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