Extreme environments, particularly hot deserts and tropical rainforests, pose distinct challenges to the organisms inhabiting them. The flora and fauna in these ecosystems have undergone evolutionary adaptations to ensure not just survival but thriving success.
Hot Deserts
Hot deserts are typified by searing temperatures during the day, cooler nights, sporadic rainfall, and intense ultraviolet radiation. Organisms here are up against challenges such as dehydration, extreme temperature fluctuations, and a general scarcity of resources.
Plant Adaptations in Deserts
- Deep and Wide Root Systems: Plants like the Saguaro cactus feature expansive root systems that spread out wide or grow deep into the ground to absorb maximum water during the infrequent rain.
- Succulent Leaves and Stems: Storing water is crucial. Plants such as the Aloe vera store water in their fleshy leaves and stems, allowing them to endure prolonged periods without rainfall.
- Waxy Cuticles: This adaptation gives many desert plants, such as the Prickly Pear cactus, a shiny exterior. It's not just for aesthetics; this waxy surface reduces transpiration, conserving water.
- Reduced Leaf Surface Area: By having smaller leaves or spines, desert plants like the Joshua tree minimise the surface area exposed to the sun, thereby decreasing water loss through transpiration.
- Photosynthesis Modifications: Some desert plants, like the Agave, undergo CAM (Crassulacean Acid Metabolism) photosynthesis, where they open their stomata at night to reduce water loss.
Desert agave (Agave deserti)
Image courtesy of Randal
Animal Adaptations in Deserts
- Nocturnal Behaviour: To circumvent the daytime heat, many desert animals, including the Desert Hedgehog, are primarily active during the cooler nights.
- Efficient Water Usage: The desert jerboa, for instance, excretes highly concentrated urine and dry faeces to retain as much water as possible.
- Burrowing: Many desert animals, like the spadefoot toad, burrow into the ground to escape the high daytime temperatures and emerge at night to feed.
- Heat Tolerance: The desert ant can survive temperatures that would be lethal to many other organisms, thanks to specialised proteins that protect its cells.
Egyptian jerboa (Jaculus orientalis)
Image courtesy of Николай Усик
Tropical Rainforests
The lush tropical rainforests, although replete with rainfall and consistent high temperatures, present their own set of challenges: thick canopies creating dim understoreys, fierce competition for resources, high humidity, and a multitude of predators.
Plant Adaptations in Rainforests
- Large Broad Leaves with Drip Tips: The larger surface area, as seen in plants like the rubber tree, helps capture more sunlight in the dim understorey. Drip tips aid in quickly shedding water, preventing rot.
- Buttress Roots: Emergent trees like the kapok tree develop flared roots. These provide both stability in the shallow, nutrient-poor soil and an increased area to absorb nutrients.
- Epiphytic Growth: Epiphytes like orchids grow on larger trees, using them as a platform to reach sunlight without being parasitic.
- Fast Growth: With so much competition for sunlight, many rainforest plants grow rapidly. The bamboo plant, for instance, can grow up to 91 cm in a single day under optimal conditions.
Plants of rainforest
Image courtesy of Hubertl
Animal Adaptations in Rainforests
- Arboreal Adaptations: Tree-dwelling or arboreal animals like the orangutan have developed strong limbs, prehensile tails, or specialised hands and feet for grasping branches.
- Camouflage and Mimicry: Predation is a significant threat. Animals like the leaf-tailed gecko and the owl butterfly have evolved to resemble their surroundings or other larger, more dangerous animals.
- Poison Production: Creatures like the poison dart frog produce potent toxins as a defence against predators. Their vivid colours act as a warning sign.
- Echolocation: In the dense forest where vision can be limited, animals like fruit bats use echolocation to navigate and locate food.
Detailed Examples of Named Species and their Adaptations
- Camel (Camelus dromedarius):
- Hump: Contrary to popular belief, camels' humps store fat, which can be metabolised to produce both water and energy.
- Nasal Adaptations: Camels can close their nostrils during sandstorms. Their nasal passages are also equipped to trap moisture from their breath.
Camel (Camelus dromedarius)
Image courtesy of Jjron
- Toucan (Ramphastos toco):
- Large Beak: While it aids in feeding, the beak is also a heat dissipation tool, helping the toucan regulate its body temperature.
- Feet Adaptations: Their zygodactyl feet (two toes facing forward and two facing backward) provide a firm grip on branches.
Toco toucan (Ramphastos toco)
Image courtesy of AntanO
FAQ
High humidity can be challenging for animals as it affects body temperature regulation and could potentially lead to overheating. Rainforest animals have evolved various strategies to deal with this. Many animals are arboreal, living in the canopy where there's more airflow and slightly less humidity. Some, like tree frogs, have developed special skin adaptations to regulate water intake and prevent dehydration. Others, such as the jaguar, remain inactive during the hottest parts of the day, conserving energy and reducing metabolic heat production. Certain species also utilise water sources like streams or puddles for cooling down and maintaining body temperature.
Buttress roots are large, wide roots on all sides of a shallowly rooted tree. Typically found in tropical rainforests, these roots offer two main advantages. Firstly, they provide stability to trees that grow very tall in search of sunlight. Rainforest soils tend to be thin and nutrient-poor due to constant rain leaching away the nutrients. As a result, trees cannot anchor deep roots for support and instead spread them out. These extended roots act as 'props' to hold the tree upright. Secondly, the increased surface area of these roots enables the tree to absorb more nutrients from the thin topsoil layer, providing the necessary nutrients for growth.
While both hot and cold regions can be classified as deserts based on precipitation levels, their temperature profiles are vastly different. Typical cacti, like the Saguaro, are adapted to withstand intense heat and prolonged periods of dryness but are not equipped to handle the freezing temperatures of cold deserts. Cold desert plants, such as certain succulents and grasses, have evolved different sets of adaptations. These adaptations might include deeper root systems to tap into underground water sources or the ability to go dormant during the coldest periods. Each desert type presents its own set of challenges, and its flora reflects those specific needs.
Desert animals have evolved various strategies to find food in their resource-limited environments. Many are omnivores, broadening their dietary options. Some, like the desert tortoise, can go for long periods without food, storing energy in fat reserves. Many desert animals are also nocturnal, hunting or foraging during the cooler nights when their prey or plant foods might be more active or accessible. Some animals, such as the Fennec fox, have heightened senses, allowing them to detect prey from great distances. Moreover, certain desert animals can metabolise fats in ways that produce water as a by-product, slightly reducing their need for external water sources.
Desert plants have evolved a unique method of photosynthesis called Crassulacean Acid Metabolism (CAM) photosynthesis. Unlike most plants which open their stomata during the day to take in carbon dioxide, CAM plants open their stomata primarily at night. This nocturnal opening of stomata helps the plant to reduce water loss due to lower night-time temperatures and humidity. The carbon dioxide taken in at night is stored as an acid and then used during the day to complete the photosynthesis process. This adaptation allows them to optimise water conservation while still getting the carbon dioxide they need for photosynthesis.
Practice Questions
Plants in hot deserts have evolved numerous strategies to cope with water scarcity. One prominent adaptation is the development of succulent leaves and stems, as seen in plants like the Aloe vera. These structures store water, allowing the plant to endure prolonged drought periods. Another adaptation is the presence of waxy cuticles on their surfaces. This waxy layer acts as a barrier, minimising water loss from transpiration and reflecting excessive sunlight to prevent overheating. In tropical rainforests, animals like the three-toed sloth have evolved to be arboreal, possessing long claws that allow them to easily grasp and move along tree branches. Their slow movement conserves energy in an environment where nutrients can be scarce. Additionally, animals such as the poison dart frog showcase bright, vivid colours, serving as a warning to potential predators of their toxicity. These colours signal danger, ensuring that the frog is left undisturbed by potential threats.
Camouflage is an essential survival strategy employed by organisms to blend into their surroundings, thus evading predators. In hot desert environments, the desert locust uses its sand-coloured exoskeleton to seamlessly blend into the desert landscape. This colouration makes it harder for predators to spot the locust, especially during the daytime when they are most active. In tropical rainforests, where the environment is lush and densely vegetated, the leaf-tailed gecko is a prime example of camouflage in action. Its body closely resembles the appearance of a dead leaf, complete with patterns mimicking leaf veins. When stationary, this gecko becomes virtually indistinguishable from the forest floor, safeguarding it from potential predators that might prey on it.
