Amphibians: Nature’s Dual-Life Wonders
What are the defining characteristics of amphibians?
Amphibians are cold-blooded vertebrates that typically start their lives in water and transition to living on land. Key characteristics include undergoing metamorphosis from an aquatic larval stage (like tadpoles) to a terrestrial or semi-aquatic adult form, possessing moist, permeable skin crucial for respiration and absorbing water and oxygen, and being ectothermic (cold-blooded), relying on external sources to regulate their body temperature.
The amphibian class is divided into three primary groups: Frogs and Toads (Anura), which are the largest and most recognisable group, characterised by powerful jumping legs and a tailless adult form; Salamanders and Newts (Caudata/Urodela), which are elongated and resemble lizards but lack scales and possess tails in adulthood; and Caecilians (Gymnophiona), the least known group, which are legless and worm-like, primarily found in tropical regions.
Amphibians play significant roles in their ecosystems and are often seen as bioindicators due to their sensitivity to environmental changes. They contribute to pest control by eating insects, serve as a food source for various animals, contribute to nutrient cycling, and their skin and regenerative abilities are studied for potential medical applications.
In Britain, the main native amphibian groups are frogs/toads and newts. Specific native species found in the Sidmouth area include the common frog and the common toad. The palmate newt is also mentioned as thriving and breeding well in the Lower Knapp Pond Reserve in Sidmouth, and is noted as favouring heathland habitats. The smooth newt is also likely to be found in garden ponds and locations like the Knapp nature pond. The great crested newt is a scarce native species under conservation efforts.
Amphibians are among the most threatened animal groups globally, facing significant challenges. Primary threats include habitat destruction and fragmentation due to deforestation and urbanisation, pollution from pesticides and chemical runoff, climate change which disrupts breeding cycles and habitats, invasive species leading to competition and disease spread, and diseases such as the highly virulent chytrid fungus (Batrachochytrium dendrobatidis), which has caused widespread declines and extinctions.
Various initiatives are underway to address amphibian decline. These include habitat restoration and protection to ensure suitable environments, captive breeding programs to safeguard endangered species, public education campaigns to raise awareness, and scientific research focused on understanding and mitigating threats like the chytrid fungus, including the development of treatment strategies.
Female frogs begin producing eggs in the autumn and throughout the winter. If a predator like a grass snake or heron eats a frog full of eggs, the eggs can swell in the predator's stomach juices. This swelling can cause the predator to regurgitate the egg mass. These regurgitated masses, when deposited in a wet location, swell into clear, jelly-like lumps known as 'star jelly', which are essentially masses of frog spawn without fertilised ovules.
Climate change significantly affects amphibians by disrupting their breeding cycles and migration patterns through altered temperatures and precipitation. Rising temperatures can desynchronise their breeding times, while changes in rainfall can cause ponds to dry up or lead to increased flooding. More frequent and intense extreme weather events further destabilise their already fragile habitats.