Amphibians are unique creatures that rely on water for their survival. If you’re wondering why frogs, salamanders, and other amphibians need to live near ponds, lakes, or other water sources, read on to uncover the details.
If you’re short on time, here’s the quick answer: Amphibians have moist, permeable skin that they need to keep wet in order to breathe and prevent dehydration. They also lay their eggs in water.
The Crucial Role of an Amphibian’s Skin
Permeable Skin Absorbs Water and Oxygen
Amphibians have very permeable skin that allows them to absorb moisture and oxygen from their environment. Their skin contains many blood vessels close to the surface, allowing for the easy passage of water, electrolytes, and gases.
This is essential for amphibians as they do not drink water through their mouths like mammals – they absorb it directly through their skin.
Amphibians also breathe partially through their skin, which needs to be kept moist in order for respiration to occur properly. Their skin acts as an auxiliary breathing organ to supplement their primitive lungs.
If their skin dries out, gas exchange cannot happen efficiently and the amphibian will suffocate.
Susceptibility to Dehydration
Because amphibians have such permeable skin, they are very prone to dehydration if they spend too much time out of water. Within only a few hours, most amphibians will become lethargic, stressed, and eventually die without access to an aqueous environment that keeps their skin moist.
Terrestrial and arboreal amphibians have adapted to minimize water loss through their skin with features like hardened skin on their bellies or feet. However, even these species need constant access to moisture like damp hideaways, dew, rain, or small streams in order to survive.
Ample Moisture Enables Gas Exchange
For efficient respiration to occur through an amphibian’s skin, there needs to be ample moisture present. A slimy mucous keeps their skin perpetually wet, ensuring oxygen from the external environment diffuses in while carbon dioxide diffuses out.
According to studies, depriving amphibians of moisture severely impairs their ability to exchange gases, sometimes slowing respiration by 50% or more depending on the species. Access to water sources keeps mucous production active and improves cutaneous respiration.
Additionally, some fully aquatic amphibians like mudpuppies actually have gills present at some stage of their lifecycle. For these species, access to water is plainly critical for gaseous exchange via gills in the same way that fish require water to respire.
Aquatic Eggs and Larvae
Most Amphibians Reproduce in Water
The vast majority of amphibians return to bodies of water like ponds, lakes, and streams to breed and lay their eggs. Over 90% of amphibian species reproduce through an aquatic process where females lay gelatinous egg masses in the water, which are then fertilized externally by the male (Roughgarden, 2022).
This reproductive dependence on water is due to the fact that amphibian eggs lack waterproof outer membranes and would desiccate if laid on land. Aquatic habitats keep the eggs moistened and able to develop (Townsend & Stewart, 2022).
After hatching, young amphibians exist as larvae or “tadpoles” which must also live underwater, breathing through gills and propelling themselves with tails. Tadpoles eat algae and plants until their lungs develop and they morph into juvenile, air-breathing, four-legged amphibians, a process called metamorphosis.
This transformation prepares them for adulthood on land. Still, proximity to water remains crucial to keep their skin moist (AZ Animals, 2023).
Vulnerable Eggs and Larvae
Amphibian eggs and tadpoles face threats from predators like insects, fish, birds, and other amphibians who take advantage of the defenselessness of these early life stages. Tadpoles also risk desiccation if water levels drop too low from drought or drainage.
These vulnerabilities make choosing the right aquatic site for breeding essential (AmphibiaWeb, 2023).
Human activities often degrade and pollute wetland habitats critical for amphibian reproduction. Runoff contaminated with chemicals, sediment, or nutrients can all negatively impact egg and larval development.
Protecting and restoring breeding ponds and wetlands is thus vital for preserving amphibian populations (Lannoo, 2005).
Few Exceptions Among Amphibians
There are a handful of exceptions among amphibians that bypass laying eggs in water. Some tropical frog species in the family Hemisotidae give birth to live young that develop as embryos inside the mother’s body after internal fertilization.
But even these frogs require moisture to keep their skin hydrated (Encyclopedia Britannica, 2023).
Parental care of terrestrial eggs is also seen in some amphibian species like Australia’s gastric-brooding frogs and South America’s Darwin’s frogs, where fathers watch over eggs until they hatch. Nonetheless, the larvae still need water after emerging and are transported safely there by a parent!
So most amphibians remain dependent on aquatic habitats during reproduction despite evolutionary adaptations by a few unique groups (Beebee & Griffiths, 2005).
The Diversity of Amphibian Habitats
Ponds, Lakes, Streams and Wetlands
The majority of amphibians live in or around freshwater habitats like ponds, lakes, streams, and wetlands. These aquatic environments provide a place for amphibians to lay their eggs and for their offspring to develop as larvae or tadpoles.
For example, most frogs lay gelatinous egg masses in still or slow-moving water sources. Their tadpoles then swim and feed in these waters until undergoing metamorphosis into adults.
Some critical statistics on amphibians in aquatic habitats:
- Over 80% of amphibian species have an aquatic larval stage
- 70% of amphibians live in rainforests near streams and ponds
- Wetlands support a greater diversity of amphibians than any other ecosystem in North America
Having access to aquatic breeding areas and resources is essential to the survival and proliferation of most amphibian species. Even terrestrial dwelling adults will migrate to mate and lay eggs in ponds or wetlands.
Adaptations for Drier Environments
While humidity and access to water sources are critical for their survival, some ingenious amphibians have adapted to thrive in drier areas. Desert rainfall frogs in Australia, for example, can wait years confined underground until sensing rain vibrations above, emerging only to frantically breed and lay eggs in ephemeral rain pools.
Other desert amphibians like spadefoot toads have accelerated life cycles, able to metamorphose from eggs to adulthood within weeks to take advantage of short-lived desert rain pools. Pretty nifty adaptive strategies!
The Need for Multiple Habitats
Most amphibians require suitable habitats for each stage of their lifecycle: aquatic breeding pools, terrestrial refuges, and humid foraging grounds. Habitat loss and degradation to any critical area can devastate local populations.
Maintenance of habitat connectivity facilitates migration and long-term survival.
To learn more on the importance of habitat diversity for amphibians, check out these great resources from U.S. Fish & Wildlife and National Wildlife Federation.
Conclusion
In summary, amphibians evolved with permeable skins that make them reliant on staying wet and lay vulnerable eggs that develop in water. While some species can travel further from water sources and tolerate drier conditions at times, all amphibians need access to aquatic habitats in order to survive.
