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Amphibians Feed On Arthropods Biology Essay

In nature everything works according to the life cycle which has been stabilized through the centuries. Every single unit of the ecosystem is crucial to maintain life in the planet as it is a piece of the food chain and precious gear to the mechanism for the equilibrium of a healthy environment. In today’s world, human does not realize that is a special element of the ecosystem interacting with it and influencing it. Much of the fauna and important cog in the mechanism mentioned is the herpetofauna, in other words, reptiles and amphibians. Apart from their role and usefulness in their natural environment, animals of the herpetofauna play an important role in human life by protecting crops and exempt from their enemies by controlling the populations of rodents and insects. The vast majority of amphibians feed on arthropods such as insects reducing the populations of arthropods affecting fields such as Crickets, grasshoppers, etc.

Amphibians are primitive vertebrates and belong to the class Amphibia. Originally they are born and grow in the water, where they breathe through gills. The majority of amphibians lay eggs in a gelatinous sheath. These are commonly applied to the water, where they develop in animals that differ too much from their parents. These aquatic larvae (tadpoles) spend a long time feeding and then the young undergo metamorphosis from larval form with gills to an adult air-breathing form with lungs. Moreover, amphibians are poikilotherms and either live close to the temperature of the surrounding air or water or employ heat by laying on surfaces heated by the sun. In very cold conditions or when the sun is hidden, their activity may be minimized, however this disadvantage is offset by the fact that a very little or no internal heat needs to be produced , so amphibians can make it consuming a very little amount of food. As a function of the external heat for the activity, this animal group cannot remain active when the temperature is very low and in very cold areas should fall into hibernation. The time remaining inactive vary depending on local conditions; in the north can reach up to two thirds of the year, while in southern countries some items may not fall at all in hibernation. Most amphibians are active during the day and others are active only during the afternoon and others are nocturnal.

Amphibians are known for about 400 million years. There are currently 6,981 species of amphibian which are devided into 3 major orders; Anura (frogs and toads), Caudata (salamanders and newts) and Gymnophionia (caellians). Therefore, there are seven amphibian species that inhabit the British Isles including the common frog (Rana temporaria), the common toad (Bufo bufo), the natterjack toad (Bufo calamita), the pool frog (Pelophylax lessonae), the smooth newt (Lissotriton vulgaris), the palmate newt (Lissotriton heleticus) and the great crested newt (Lissotrition cristatus). Moreover, amphibians in Britain that their populations may be in danger are legally protected. According to British legislation natterjack toad (Bufo calamita) and great crested newt (Lissotrition cristatus) protected amphibian species by the Countryside Act 1981, the National Biodiversity Action Plan and the European Conservation Regulation 1994.

Nevertheless, many amphibian species are thought to be threatened with extinction and others face severe population declines. There is a number of amphibian diseases cause mortality and incapacity in amphibians including chytridiomycosis which appears to be the major factor in dramatic amphibian declines in many parts of the world. Chytridiomycosis is an infectious disease caused by a fungus called Batrachochytrium dendrobatidis. The disease is caused by a fungus - and is often referred to as chytrid or the chytrid fungus - which can potentially kill all of the individuals in a population. Research in chytridiomycosis is still in its infancy. Whilst some aspects are now well understood, significant knowledge gaps remain. For example there are some species which are surprisingly unaffected, the actual mechanism of mortality and what factors are required to trigger mass mortality.

In order to be able to measure and control the changes in the populations and conservation status, amphibians are becoming subject to co-ordinated monitoring and surveying programmes.

Common frog (Rana temporaria)

Adult common frogs can reach a body length of 6 to 11 centimeters and are able to jump up to 1.5 meter. Their average weight is 13g and their backs and flanks have a variation in colour, with yellow-green, grey-brown, brown and grey. As large frogs their body is less slender than other species of brown frogs and their snout is rounded short and blunt. However, common frogs are known to be able to lighten and darken their skin in order to match their surroundings. Common frogs' flanks, limbs and backs are covered with irregular dark blotches and they usually got two large spots temporary on both sides of the head, very dark and mask mode; that go from the NaReS up the armpits a cross the eye and the ear drum. The tympanum is large and clear, separate of the eye with a diameter corresponding to two thirds of this. Vomerian teeth present. Moreover, males differ from females as they possess two internal vocal sacs and during mating season their throats usually turn white. Also their fist finger is longer than the second. Common frogs have relatively short legs and possess webbed feet. The belly and bottom of the legs are pale, yellowish or whitish. When the rear leg is stretched over the body, the tibio-tarsal articulation usually reaches the eye, but does not reach the tip of the snout. Interdigital membranes are small, usually covering half the length of the fingers.

Common frog is widespread throughout much of Europe and it is catholic in its range of breeding sites. It is most often found in garden ponds and unshaded ponds with or without fish. In Britain they are very common and have been introduced to Ireland, where their distribution is patchy.

Furthermore, common frogs breed in shallow, still, fresh water such as ponds, with breeding commencing in March. Males arrive at breeding site first and start calling to attract females. During the mating season males form amplexus with females, a form of pseudocopulation in which a male amphibian grasps a female with his front legs as part of the mating process. Common frogs breed with external fertilization and their clumps consist between of 1,000 to 2,000 eggs and need 2-3 weeks to hatch. When eggs hatch tadpoles feed on algae, detritus and later on carrion. Tadpoles metamorphose after 2-3 months to adult frogs.

Common toad bufo bufo

Common toad is a nocturnal amphibian and spends its day hide under shade. They are active during the night time and they mainly feed on small arthropods. Common toad can reach about 18cm in length. The head is broad with a wide mouth below the terminal snout. There are no teeth and the bulbous eyes have yellow coloured irises. Behind the eyes are two bulging regions , the paratoid glands which contain a noxious substance, bufotoxin which is used to avoid most predators since it has a very strong taste and smell, but not strong enough to keep away other predators such as snakes.

Common toad is widespread throughout Europe, Asia and North America. Lives in a big variety of habitats such as woodlands, meadows and garden ponds. Also it is a widespread amphibian found throughout Britain in farm ponds, reservoirs, fish ponds or village duck ponds. Sadly these types of freshwater body are threatened in many parts of the UK.

During the breeding season they are found in lakes, where the male climbs on the back of the female embracing it and therefore fertilizing the eggs. Females are larger than males and can lay 2 string of eggs at the same time which can be 5 meters in length. The larger females can be shoveled up to 7,000 eggs. This species is least of concern.

Natterjack toad (Epidalea calamita)

Natterjack toad is a rare amphibian species in the UK. They can reach about 70cm in length and are distinguished by common toads by their smaller size and a yellow line down the middle of their back. They have a green-beige dorsal colour and dorso-laterla folds are abscent. They run rather than crawl and males have a high pitched call.

Populations of the toad extend through seventeen European countries. In mainland Europe, Natterjack lives inland in a variety of habitats. However, Natterjacks are rare in Britain. They can be found in southwest Ireland, pockets of Norfolk and Lincolnshire, along the coast between Lancashire and Dumfries and areas of Hampshire and Surrey. In Britain the Natterjack lives exclusively in sandy places, such as coastal dunes and lowland heaths. In Cumbria and Scotland populations are also thriving on upper saltmarshes and upland moor.

Natterjack toad breeds from March to May. Males always arrive at breeding site first and start calling to attract females. Females lay a string of eggs similar to the Common Toads, but distinguishable as the string contains a single row of eggs unlike the double row typical of Bufo bufo. They usually take advantage of small pools and lay their eggs, where there is less risk of predators. After 2-3 weeks the eggs hatch and the young tadpoles start feeding in the pool until they reach metamorphosis when they change appearance and become adult natterjack toads.

Smooth newt (Lissotriton vulgaris)

Smooth newts’ habitat is ponds in dunes and heathlands. They can tolerate fish but prefer ponds with desiccate occasionally. Both sexes are of similar size up to 10 cm in length and have brown spotted throats and ventral surface yellow/orange with distinct spots. However, males posses a swollen cloaca, and develop wavy crest which is continuous with tale in the breeding season. Females dorsal varies brown/black (similar to the palmate newt).

Moreover, smooth newts are very common and widespread. They are found throughout Europe except the far north, areas of Southern France. Also they are the most common of the newts within Britain, occupying a range of habitats from Scotland down to the southern countries. Smooth newts exhibit a protracted breeding strategy with both sexes remaining in breeding ponds for many months. This species will tolerate many pond types from garden ponds and woodland to water-bodies in grassland habitats. During breeding season (February - June) smooth newts become more strikingly and colorfully marks with vivid spots and orange bellies. Males perform sexual display, waft tail and pheromones, to attract females. Then they deposit spermatophore on substrate and females collect it for internal fertilization. Females lay 200-300 eggs, individually wrapping each within a leaf. After 2-3 weeks eggs hatch to a tadpole. Then tadpoles survive by eating the food reserves contained within their yolk sacs. After they begin eating plankton and later insect larvae and mollusks.

Palmate newt (Lissotrition helveticus)

The Palmate newt is a relatively small species, males reaching only about 8 cm and females 9 cm. Both sexes have pale, pink throats. Males posses a swollen cloaca and develop a filament to the tail, webbed back feet and ridge along back in breeding season. In addition they have a tail filament, which reduces water turbulence and heavily palmate hind toes. This gives the male an increased swimming speed with which to chase after females. On the other hand, females are similar to females of smooth newt but face has more distinct black stripes. Although, palmate newts are more selective in breeding sites than smooth newts favoring instead more acidic woodland and upland water-bodies. Also they prefer ponds which do not desiccate frequently. During the breeding season (April-May) they are usually active day and night.

The Palmate Newt is a species of newt found in most of Western Europe. In Britain they are more often found in north and west of the country.

Great crested newt (Triturus cristatus)

The largest of the newts, the great crested newt reaches up to 15cm in length. It has a grey-brown back and it is covered with darker coloured spots sp that they appear almost black in colour. Males can be distinguished from females during the breeding season by the presence of a distinct jagged crest, which dips between the body and the beginning of the tale. Females lack a crest but are slightly larger than males and have a yellow/orange stripe along the lower edge of their tail.

The range of the distribution of Great crested newt extents from Britain and Brittany, west of Europe, north of the Alps and the Black sea. This species has a widespread, but patchy distribution across Britain and has population declines in recent years due to habitat destruction and fragmentation. Great crested newts are more exacting in their habitat requirements than other newt species, preferring deeper, larger ponds with open water in which to perform their courtship display.

Breeding is similar to that of other newts. On arrival to ponds males deposit a spermatophore from his cloaca and then the female picks up the spermatophore by her cloaca so mating is done without direct contact. Research has shown that that females exhibit mate choice, prefering to take spermatophores from males with larger crests.

Survey techniques

Amphibian surveying techniques have been designed to reveal the ecology and habitat requirements of amphibian species while they may be either nocturnal or secretive or diurnal or arboreal and even switch between habitats at different stages of their life.

There is no one standard method for sampling amphibians in the field. Every single technique comes with its own set of assumptions, advantages and disadvantages, and it is not uncommon for a research program to make use of multiple methods. Instead, amphibian researchers develop tools for gathering baseline data as they gain insight into the behaviour and life history of their study species. Basic survey methods that have been used include visual search during daytime, netting, refugia search, egg search, torching bottle trapping and drift fencing and pitfall trapping .

Visual is a method by which the researcher is looking for presence of species at pond by daylight. This technique has the advantage that there is no need for a license if animals are not disturbed, no equipment is required and it can be applied in daylight. However, sometimes animals may not be seen even if they are present, the identification of newt species may be difficult and this technique gives no idea of population size.

Netting is the capturing of amphibians by daylight with a dip net. This technique can be applied in daylight and certain species are easy to catch. Also it allows accurate identification. However, some species such as the great crested newts are difficult to catch and need a licence as well. This method gives no idea of population size and it can cause disturbance to the pond.

Refugia search is the technique of searching for amphibians to their refuge by turning over surrounding stones. It can be done in daylight and it gives accurate identification without the need of any equipment. Although, refugia search gives no idea of population size and licence is required for great crested newts.

Egg search is the method of visually searching for eggs. It can be applied in daytime without any equipment. It is a very quick method to confirm the presence or absence of the most of species without disturbing the pond. Though, eggs may not be present if the visit is done at a wrong time of the year. Another disadvantage of this method is that palmate newt eggs are impossible to be distinguished from smooth newt eggs and it gives no idea of population size.

Torching is a method of visually searching for amphibians by nighttime. There is no need for a license while this method needs minimal equipment and it is very fast without disturbing the pond. On the other hand torching is not the best technique for the identification of females of palmate and smooth newts. Also it must be done at night and sometimes in windy and wet conditions.

Bottle trapping is the set of bottle traps overnight and their collection next morning. It allows accurate identification and it can be carried out in weedy or turbid conditions. It makes a minimal disturbance to the pond and it gives estimates of relative abundance and actual population size. However, asphyxiation for animals is possible and male bias in hypothalamus. This technique is only possible for surveying newts.

Drift fencing and pitfall trapping is a technique by which the researcher encircles the pond in order to catch all immigrating/emigrating individuals and it makes possible to study population sizes and dynamics. Nevertheless, this is a license required and time consuming method. In addition, pitfall traps need to be checked every day.

Moreover, surveying amphibians is a very accurate and précised process. Each amphibian has its own habitat and need a special treatment. So survey techniques may differ from one species to another.

For newts torching is the simplest method as newts are nocturnal and more active by night. Also bottle trapping is effective but several visits need to be carried out. Dip netting can be standardized but does not give indication of population size.

Surveying for toads and frogs need a visit by day early in season to carry out risk assessment, consider access and terrain and carry out a visual survey technique.

To conclude, Great crested newt is a keystone species according to Biodiversity Action Plan (BAP) and European Protected Species. It has a disproportionately large effect on its environment relative to its abundance. Great crested newts play a critical role in maintaining the structure of their ecological community, affecting many other organisms in an ecosystem and helping to determine the types and numbers of various other species in the community.


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