AMPHIBIANS (Frogs and toads) Explained: In-depth Guide
Objectives
Amphibians (Toads and Frogs)
Phylum: Chordata
Sub-phylum: Vertebrata
Class: Amphibia
Main Habitats of Frogs and Toads
Frogs and toads, belonging to the class Amphibia, are found in a variety of habitats worldwide. Their ability to live both in water and on land (dual life) makes them adaptable to diverse environments. Here are the main habitats where frogs and toads are typically found: They are poikilothermic (cold-blooded) vertebrates, meaning; their body temperature depends on the temperature of their environment.
1. Freshwater Habitats
- Ponds, Lakes, and Streams: Many frogs and toads begin their life cycle in aquatic environments, laying their eggs in water. These bodies of water provide a safe environment for the eggs and developing larvae (tadpoles).
- Wetlands and Marshes: These areas, with their abundant vegetation and water, offer ideal breeding and feeding grounds for frogs and toads. The moist environment is crucial for their skin, which needs to stay moist for respiration.
- Rivers and Creeks: Frogs and toads may also be found along riverbanks and creeks, where they can access both aquatic and terrestrial resources.
2. Forests
- Rainforests: Tropical rainforests are home to a wide variety of frog species, many of which are adapted to the moist, humid environment. These forests provide ample food, shelter, and breeding sites.
- Temperate Forests: In cooler climates, temperate forests provide habitats for species that can survive seasonal changes, including hibernation during colder months.
- Deciduous and Coniferous Forests: Frogs and toads can be found in both deciduous and coniferous forests, where they take advantage of the leaf litter, underbrush, and forest floor for shelter and hunting.
3. Grasslands and Savannas
- Prairies and Meadows: Some species of frogs and toads are adapted to living in grasslands, where they may find temporary ponds and streams during rainy seasons for breeding.
- Savannas: In these open areas, frogs and toads can often be found in seasonal water bodies and rely on burrows or other forms of shelter to protect themselves from predators and harsh weather conditions.
4. Deserts and Arid Regions
- Oases and Temporary Pools: In arid environments, frogs and toads may be found near oases or in ephemeral water bodies that form after rains. They have adapted to survive in these harsh conditions, often entering a state of dormancy (aestivation) during dry periods.
- Adaptations for Dry Conditions: Species in these areas often have special adaptations, such as the ability to retain water or burrow underground to escape extreme temperatures.
5. Urban and Suburban Areas
- Gardens and Parks: Frogs and toads can also be found in urban and suburban areas, particularly in gardens, parks, and around artificial ponds and water features.
- Drainage Systems and Sewers: Some species have adapted to urban environments, using drainage systems and sewers as habitats.
6. Coastal and Marine Areas
- Mangroves and Coastal Wetlands: Certain species are adapted to brackish water environments, such as mangroves and coastal wetlands.
- Saltwater Adaptations: Although rare, some species have adaptations that allow them to live in or near saltwater environments.
Structure of a Toad
The body of toad consists of only head and trunk. It has short, round neckless body with dry skin and no tails.
It has large flat head with wide mouth and sticky tongue, prominent bulging eyes and a pair of nostrils above the mouth.
Each eye has movable lower eyelid. The lower lid has a transparent fold of skin called nictitating membrane. This moves over the eye to clean, moisten and protect it.
Behind the eyes are circular ear drums or tympanum. The eardrums pick up sound vibrations in air and in water, which enable the toad to hear.
Two pairs of limbs arise from the trunk. The forelimbs are shot and stout with four digits which are not webbed. The forelimbs absorbs the shocks of landing after hopping. The hind limbs are longer and more muscular with five webbed digits. They push and lift the toad off the ground when hopping. The webbing offers a large surface area to push against water when swimming.
At the posterior end of the body is the cloaca, for discharging feces, sperms or eggs.
Nutrition in Toads
Locomotion in Toads
The feet have adaptations for movement both on land and in water.
a. On land, Toads move by hopping or leaping and crawling. The long, muscular folded hind limbs are straightened to push and lift the toad off the ground when hopping. The forelimbs absorb the shocks of landing after hopping. The toads usually move by crawling with the limbs moving diagonally.
b. In water, toads swim by using the powerful hind limbs. The webbed feet increase the surface area that pushes against the water. The forelimbs are used in steering.
Excretion in Toads
Respiration in Toads
Reproduction in Toads
Egg: During the breeding season, the male croak loudly to attract a female. The male mounts on the back of a female, gripping her under the arms with his forelimbs. In this way, he is carried around in the water by the female, sometimes for many days. The female lays eggs, the male releases sperms to fertilize them. Fertilization is external. The eggs are surrounded by a transparent gelatinous layer or a string of jelly. The eggs are hatch into free-living larvae called tadpole
Functions of the jelly
Tadpole
It has oval body, cartilaginous skeleton, gills and large flattened tails with fins for swimming. Tadpole develops gill pouches that cover the gills. It has a relatively long, spiral shaped intestine. Tadpole undergoes some changes during development into adult by a process called metamorphosis. At metamorphosis, the spiral‐shaped mouth with horny tooth ridges is reabsorbed together with the spiral gut. It develops a large jaw, and its gills and gill sac disappear. Eyes and legs grow quickly, and a tongue is formed. The tail is reabsorbed by apoptosis.
Differences Between Toads and Frogs
While toads and frogs both belong to the order Anura, they have distinct differences in their physical characteristics, habitats, behavior, and physiology. These differences can often help in distinguishing between the two, although it's important to note that the distinctions are not always absolute and there are exceptions.
1. Skin Texture
Frogs: Frogs typically have smooth, moist, and often shiny skin. The moisture is essential for their respiration and is maintained by living in or near water sources. Learn more about the importance of frog skin from FrogLog.
Toads: Toads generally have dry, rough, and warty skin. This texture helps reduce water loss, allowing them to live in drier environments. The "warts" are actually glands that can secrete toxins as a defense mechanism.
2. Body Shape and Size
Frogs: Frogs usually have a more streamlined, slender body shape. They tend to have longer legs, which are adapted for jumping and swimming.
Toads: Toads typically have a stockier, more robust body. Their legs are shorter compared to frogs, which makes them more suited for walking or hopping rather than long jumps. For detailed comparisons, refer to Frog vs. Toad by Britannica.
3. Habitat Preferences
Frogs: Frogs are generally found in moist environments, such as ponds, lakes, streams, and wetlands. They require a nearby water source for reproduction and to keep their skin moist. Smithsonian's National Zoo offers more insights into frog habitats.
Toads: Toads are more terrestrial and can be found in a wider range of habitats, including forests, grasslands, and even deserts. They are less dependent on water than frogs and can often be found far from water sources. Learn more from AmphibiaWeb.
4. Eggs and Reproduction
Frogs: Frogs lay their eggs in clusters or masses, often in the form of a jelly-like substance that floats on water surfaces. The eggs are typically round and transparent.
Toads: Toads lay their eggs in long chains, which can often be seen wrapped around vegetation or lying on the bottom of water bodies. The eggs are usually encased in a string-like gelatinous material.
5. Behavior and Movement
Frogs: Frogs are usually more agile and capable of making long jumps due to their long hind legs. They are also excellent swimmers and often make use of their webbed feet in the water.
Toads: Toads tend to move by short hops or walking rather than jumping. Their shorter legs are not as suited for swimming or long leaps. For more on amphibian locomotion, see Frogland.
6. Toxin Production
Frogs: While some frogs can produce toxins, they are generally less poisonous than toads. Poison dart frogs are a notable exception, producing potent toxins.
Toads: Many toads have parotoid glands behind their eyes that secrete a milky toxin as a defense mechanism. This toxin can be irritating or harmful to predators and, in some cases, humans. To learn more about amphibian toxins, visit The Reptile Database.
7. Lifespan and Longevity
Frogs: The lifespan of frogs can vary widely depending on the species, but many live between 5 and 10 years in the wild. Some species can live longer in captivity.
Toads: Toads generally have a longer lifespan than frogs, with some species living up to 15 years or more in the wild. In captivity, they can live even longer. For a deeper dive into amphibian lifespans, check Live Science.
8. Vocalization
Frogs: Frogs are often more vocal and produce a wide range of sounds, especially during mating seasons. These calls are usually loud and can be heard over long distances. National Geographic provides more information on frog calls.
Toads: Toads also vocalize, but their calls tend to be deeper and less varied than those of frogs. They are usually less vocal overall. Explore toad calls at AmphibiaWeb.
|
Toad |
Frog |
|
Slightly webbed hind limbs |
More webbed hind limbs |
|
Spawn forms strings |
Spawn forms clumps |
|
Spend more time on land |
Spend more time in water |
|
Warty skin |
Smooth skin |
|
Presence of poison gland |
Absence of poison gland |
|
Skin has less mucous glands; relatively
drier skin |
Skin has more mucous glands; slimy skin |
Differences between Tadpole and Tilapia
|
Tilapia |
Tadpole |
|
Possession of paired fin |
Possession of only caudal fins |
|
Tail relatively short |
Tail relatively long |
|
Fins have rays |
Fins have no rays |
|
Skin covered with scales |
Skin has no scales |
|
Lateral line present |
No lateral line |
|
Teeth are preset |
Teeth are absent |
Structural similarities between Tadpole and Tilapia
o Stream-line shape
o Presence of opercula
o Possession of mouth
o Possession of eye and nostril
o Possession of tail
Adaptations of Frogs and Toads for Survival in Different Environments
Frogs and toads have evolved a variety of adaptations that allow them to survive and thrive in diverse environments. These adaptations can be broadly categorized into physical, behavioral, and physiological adaptations, each helping them to meet the challenges of their habitats. Here are some key adaptations:
1. Physical Adaptations
Moist Skin: Frogs and toads have permeable skin that allows for cutaneous respiration (breathing through the skin). This is crucial for absorbing oxygen, especially in aquatic or humid environments. Their skin also needs to stay moist to facilitate this gas exchange, which is why they are often found near water sources.
Camouflage and Coloration: Many frogs and toads have skin colors and patterns that help them blend into their surroundings. This camouflage protects them from predators and allows them to ambush prey. Some species also have bright colors that serve as warning signals to potential predators, indicating that they are toxic or unpalatable.
Webbed Feet: Aquatic species, such as those living in ponds and streams, often have webbed feet that aid in swimming. The webbing increases surface area, making them efficient swimmers.
Powerful Legs: Frogs and toads generally have strong, muscular hind legs adapted for jumping and swimming. These legs allow them to escape predators quickly and efficiently.
Tympanic Membrane: Frogs and toads possess a tympanic membrane (eardrum) on each side of their head, which helps them hear and detect vibrations. This is important for communication and detecting the presence of predators or prey.
Specialized Tongues: Many frogs and toads have long, sticky tongues that they can rapidly extend to capture insects and other small prey. This adaptation allows them to feed efficiently.
2. Behavioral Adaptations
Nocturnal Activity: Many frogs and toads are nocturnal, meaning they are active at night. This behavior helps them avoid predators and extreme daytime temperatures, especially in hot or arid environments.
Hibernation and Aestivation: Frogs and toads can enter a state of dormancy to survive unfavorable conditions. In cold climates, they hibernate during winter, reducing their metabolic rate to conserve energy. In arid regions, they may aestivate during dry periods, burrowing into the ground to stay cool and moist.
Mimicry and Deception: Some species exhibit mimicry, where they resemble other more dangerous or toxic species to avoid predation. Others may use deceptive behaviors, such as playing dead when threatened.
Breeding Adaptations: Frogs and toads have diverse breeding strategies, including vocalizations to attract mates, and elaborate courtship displays. Some species engage in parental care, such as mouthbrooding or carrying eggs on their backs, to protect their offspring.
3. Physiological Adaptations
Water Conservation: In arid environments, toads often have thicker, more waterproof skin than frogs, reducing water loss. Some species can absorb water through specialized areas of their skin, known as "seat patches," to rehydrate from moist surfaces.
Toxin Production: Many frogs and toads produce toxins in their skin as a defense mechanism against predators. These toxins can range from mildly irritating to highly lethal. The presence of these toxins often coincides with bright warning coloration.
Temperature Regulation: Frogs and toads are ectothermic (cold-blooded) and rely on external heat sources to regulate their body temperature. They may bask in the sun to warm up or seek shade to cool down. Some species can tolerate freezing temperatures by producing antifreeze-like substances in their tissues.
Lung and Buccopharyngeal Respiration: While most frogs and toads have lungs, they can also perform buccopharyngeal respiration, where oxygen is absorbed through the moist lining of the mouth and throat. This is especially useful when they are submerged in water or during periods of reduced lung use.
The Role of Frogs and Toads in the Ecosystem
Frogs and toads, as members of the order Anura, play crucial roles in various ecosystems around the world. Their presence and activities contribute significantly to ecological balance, serving as key players in nutrient cycling, food webs, and as bioindicators. Here are some of the essential roles they fulfill:
1. Predator and Prey Dynamics
As Predators: Frogs and toads are carnivorous and consume a wide variety of insects and other small invertebrates. This predatory behavior helps regulate insect populations, including those of mosquitoes, flies, and other pests. By controlling these populations, they help prevent the spread of diseases such as malaria and dengue fever, which are carried by insects. This natural pest control is beneficial for both natural ecosystems and human agricultural activities.
As Prey: Frogs and toads serve as an important food source for a wide range of predators, including birds, mammals, reptiles, and even other amphibians. Their eggs, tadpoles, and adult forms are all targeted by different predators, making them a vital link in the food chain. This role supports the survival and health of many other species within their ecosystems.
2. Nutrient Cycling and Soil Fertility
Frogs and toads contribute to nutrient cycling by breaking down organic matter and redistributing nutrients within the ecosystem. When they consume insects and other invertebrates, they help decompose organic material, which is then excreted as waste. This waste enriches the soil with nutrients, promoting plant growth and contributing to the overall health of the ecosystem. Additionally, the decaying bodies of frogs and toads provide nutrients to the soil, further supporting plant life and soil fertility.
3. Bioindicators of Environmental Health
Frogs and toads are highly sensitive to environmental changes due to their permeable skin, which absorbs water and chemicals directly from their surroundings. This sensitivity makes them excellent bioindicators of environmental health. Changes in frog and toad populations can indicate the presence of pollutants, habitat degradation, or changes in climate. For example, a decline in amphibian populations may signal issues such as water pollution, chemical contamination, or ecosystem imbalances. Monitoring these populations helps scientists and conservationists identify and address environmental problems early on.
4. Ecosystem Engineers
In some ecosystems, frogs and toads act as ecosystem engineers. Their activities, such as burrowing and creating small ponds during the breeding season, can alter the physical environment. These alterations can create habitats for other organisms, promoting biodiversity. For example, the burrowing of toads can aerate the soil, facilitating water infiltration and plant root growth. Additionally, temporary pools created by frogs for laying eggs can become breeding sites for other aquatic organisms, supporting diverse aquatic communities.
5. Pollination and Seed Dispersal
While not as significant as their role as predators and prey, some frogs and toads contribute to pollination and seed dispersal. Certain species feed on nectar and pollen, inadvertently transferring these from one plant to another, aiding in pollination. Others may consume fruit and disperse seeds through their droppings, assisting in the propagation of various plant species.
6. Cultural and Economic Importance
Beyond their ecological roles, frogs and toads hold cultural and economic significance in many societies. They are often featured in folklore, literature, and art, symbolizing various themes such as transformation and fertility. Additionally, frogs are used in scientific research, medicine, and education. Their unique biological traits make them valuable in studies related to genetics, physiology, and environmental sciences
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