1. Adaptations to Arid Habitats

2. What is an arid habitat? Arid habitats: are extremely dry
receive little or no rainfall
usually have high temperatures
may suffer periodic droughts
Ask the class if they can explain what an arid habitat is.
Arid habitats:
are extremely dry – there is little water available to drink, very few plants are able to grow
receive little or no rainfall
have high temperatures – Although temperatures are generally high, they may also fluctuate a lot, being hot during the day and cold at night
may suffer periodic droughts

3. Where are arid habitats found?
Estimates suggest that arid and semi arid habitats account for more than one third of the earth’s land surface
Ask the class if they know where arid habitats might be found.
Arid habitats are actually found all over the world, and estimates suggest that arid and semi arid habitats account for more than one third of the earth’s land surface.
Map from:
Credit: U. S. Geological Survey

4. What are the challenges of living in an arid habitat?
Lack of plants
Lack of water
Lack of food
Challenges?
Temperature
Movement
Ask the class what challenges they think that species living in an arid habitat might face.
Temperatures are generally high so species need to be adapted to cope with the heat. However, temperatures can drop significantly at night, meaning species in arid habitats may also have to cope with very cold temperatures.
All animals and plants need a certain amount of water to survive, for drinking, for growth and in some cases even for reproduction. For example, most amphibians must lay their eggs in water.
Few plants are able to cope with the harsh, dry conditions in arid habitats. This can be a problem for species which rely on plants to provide them with a home, cover from predators, shade, or food. This brings us nicely on to our next point:
Lack of food. The lack of plants in arid habitats means that herbivorous (plant eating) species have less to eat. This means that arid habitats are unable to support large numbers of these species, so in turn there are also fewer prey animals for the carnivorous (meat eating) species to feed on. Finding food in an arid habitat can be a real challenge.
Movement can be difficult in an arid habitats. The landscape is often sandy or rocky, so some species have adaptations to allow them to move quickly and efficiently.
Hot
Cold

5. What is adaptation?
“the process whereby a species evolves characteristics that enable it to survive in a particular habitat”
Adaptations allow species to live successfully in their habitat
Species living in different habitats need different adaptations
Adaptations can be behavioural or physical
We have mentioned adaptation a few times now. Ask the class if anyone can explain what we mean by adaptation.
Adaptation is “the process whereby a species evolves characteristics that enable it to survive in a particular habitat”.
Adaptations allow species to live successfully in their habitat, and species living in different habitats need different adaptations.
Adaptations can be behavioural, for example something an animal does, or physical, such as a particular feature of the body that helps the species to survive.
Today we are going to consider how species in arid habitats have adapted to their environments.

6. Barrow Island: Case Study
- Approximately 70 km off the coast of Western Australia - Receives an average of 320 mm rainfall per year - Most of the island is covered by spinifex grassland - Nearly 2,600 different species have been recorded here
To investigate how different species have adapted to cope with living in an arid habitat we are going to focus on Barrow Island as a case study.
Barrow Island is located approximately 70 kilometres off the north-west coast of Western Australia, and like the mainland it has a hot, dry climate and an arid landscape.
The rainfall here is variable, but averages around 320 millimetres per year, most of which falls during the cyclone season between November and April. Much of the island is covered by spinifex grasslands and rocky outcrops.
Despite its aridity, nearly 2,600 species have been recorded on Barrow. But how are these species adapted to this harsh environment?
DESCRIPTION OF SPINIFEX GRASSLAND
Triodia is a large genus of hummock-forming grass endemic to Australia, commonly known as spinifex. It grows in arid regions. Spinifex has traditionally had many uses for Australian Aborigines, for example the seeds were collected and ground to make seedcakes, while the resin from the grasses were used as an adhesive in spear-making. Smoke signals were made to communicate with families and groups a long distance away, as burning spinifex produces a strong black smoke.

7. These images show what some of the typical habitat looks like on Barrow Island.

8. This image shows a flooded channel on the west coast of the island, a rare and important source of freshwater on Barrow.
A flooded channel on the west coast of the island, a rare and important source of freshwater on Barrow

9. Mammals on Barrow Island
Common wallaroo (Macropus robustus) Found across most of Australia, with one subspecies on Barrow Island Seeks shelter in caves and rocky outcrops Can go for a few months without drinking Licks saliva onto forearms to help it lose heat through evaporation Stops breeding during prolonged droughts, but breeds quickly in good conditions
Mammals have relatively high water requirements, as they lose water in urine and faeces and also use it to cool the body through evaporation by sweating or panting. Female mammals also need water to produce milk. In addition, mammals are warm blooded, meaning they regulate their own body temperature through metabolic processes. This requires energy, so mammals have higher food requirements than cold blooded animals such as reptiles.
The common wallaroo is a stocky kangaroo found across most of Australia. One particular subspecies, known as the ‘Barrow Island euro’, is found only on Barrow Island.
The common wallaroo shows a number of adaptations to the arid conditions on Barrow Island and across much of the mainland. For example, it uses caves and rocky outcrops to shelter from the heat of the sun. The common wallaroo can also go for as much as 2 to 3 months without drinking, surviving only on the water in the plants it eats.
The skin on the common wallaroo’s forearms is quite thin and has a rich blood supply. By licking saliva onto these areas, the wallaroo can lose heat more easily through evaporation. This species pants when hot, allowing water to evaporate from its nose and open mouth, and only sweats during exercise, stopping as soon as its rests to allow it to conserve water.
During prolonged droughts, the common wallaroo may stop breeding. The embryos of this species can also remain dormant, only developing further when conditions are favourable. In good conditions, the common wallaroo can breed quickly and soon replace any young lost to drought or predators; at any one time, the female common wallaroo can have one dormant embryo in her womb, one young in her pouch, and another, older young outside the pouch.

10. Other mammal examples
Wild Bactrian camel Many adaptations to conserve water, cope in intense heat and survive sandstorms!
Many other mammals also show a range of adaptations to arid habitats.
Camels such as the wild Bactrian camel are superbly adapted to living in deserts. They can go a week or more without water, and several months without food, and when they do find water they can drink large amounts in one go. Camels store fat in their humps, providing a source of energy while reducing the insulating effect the fat would have if distributed around the whole body. Unlike that of most mammals, the body temperature of the camel fluctuates throughout the day, allowing it to conserve water by not sweating as temperatures rise, and it can tolerate body temperatures up to 42 degrees Celsius.
Camels are also well adapted to living in sandy environments. Long eyelashes, hair inside the ears and the ability to close the nostrils helps keep sand out of the eyes, ears and nose, while wide feet allow the camel to walk on sand without sinking in. In addition, thick lips enable camels to eat prickly desert plants.
Other adaptations shown by mammals include large ears, such as those of the bat-eared fox. These provide a large surface area that helps the fox to lose excess heat.
Bat-eared fox Large ears to help dissipate heat

11. Fawn hopping mouse Can obtain water from seeds Produces concentrated urine + dry faeces Shelters in a burrow during day
Some mammals show physiological adaptations that help them to conserve water. For example, the fawn hopping mouse can turn carbohydrates from the seeds it eats into water, meaning it does not need to drink. It also produces concentrated urine and dry faeces to minimise water loss. Like many desert species, the fawn hopping mouse shelters in a burrow during the heat of the day, where conditions are cooler and more humid.
Species such as the desert kangaroo rat use a ‘nasal counterflow system’ to reduce the water lost when the animal breathes out. When hot, dry, inhaled air passes over moist surfaces inside the nasal passages, water evaporates from the surfaces and cools them. When warm, moist air from the lungs passes back over the cooler surfaces on the way out, it is cooled slightly and water condenses back onto the membrane instead of being breathed out. This process is common to many mammals, but is particularly useful for those adapted to arid conditions.
Kangaroo rats ‘Nasal counterflow system’ reduces water lost through breathing

12. Amphibians on Barrow Island
Main’s frog (Litoria maini) Only amphibian species found on Barrow Island Spends the dry season underground in a state of torpor Produces a membrane over the skin to prevent drying out Only emerges after rainfall Eggs laid in temporary pools, tadpoles develop quickly
Amphibians are usually found in damp, humid habitats as they have permeable skin, meaning that they are very susceptible to water loss and desiccation (drying out). In addition to this, most species of amphibian must return to water to breed. Eggs are almost always laid in water where the larvae then develop before metamorphosing into juveniles which are able to leave the water to spend time on land.
There is only one species of frog found on Barrow Island, Main’s frog, a species also found in some of the harshest arid habitats on mainland Australia.
Main’s frog has adapted to cope with the conditions on Barrow Island by spending the dry season burrowed underground in a state of torpor, a sleep-like state in which the body processes slow to a fraction of their normal rate.
While underground they also produce a membrane over the skin which helps them to retain moisture.
Main’s frog only emerges after the rainfall, and quickly begins to breed, laying eggs in the pools of temporary water. The tadpoles develop quickly before the pools dry out completely.

13. Other amphibian examples
Spotted marsh frog Shelters under logs and stones in the heat of the day
Water holding frog Can reabsorb water stored in its bladder or pockets under the skin
Mainland Australia is home to 208 frog species, many of which inhabit arid regions. Like Main’s frog, these species have a number of different adaptations to help them cope the limited availability of water.
Some species have adapted their behaviour, for example the spotted marsh frog shelters under logs and stones during the day to avoid the heat.
Like Main’s frog, the water holding frog also burrows underground, and stores water in its bladder or in pockets under its skin. This species was used by Aboriginals as a source of drinking water, as gently squeezing the frog in your hand encourages it to release its water, and the frog can be released unharmed.
The green tree frog is another Australian species which survives in its arid habitat by seeking refuge in any available damp space, including man-made sources of water such as pipes and toilet bowls!
Green tree frog Takes refuge in any available water sources, including pipes, water tanks and toilet bowls!

14. Reptiles on Barrow Island
Perentie (Varanus giganteus) General adaptations common to reptiles Shelters underground or in rock shelters; basks in sun in early morning and late afternoon On very hot days, may shelter in shade or climb termite mounds or shrubs to get off hot ground
Reptiles are well adapted to living in hot, dry conditions. They are cold blooded, or ‘ectothermic’, using the external environment to regulate their temperature. For example, they may bask in the sun to warm up or move into shade to cool down. This means they need less food than a warm blooded animal such as a mammal, and this helps them survive in arid environments where food is scarce.
Reptiles also have dry, scaly, relatively impermeable skin, which helps to reduce water loss. Reptile eggs have a hard or leathery shell and so don’t dry out like those of amphibians. Reptiles also reduce the water lost through excretion by excreting uric acid in a solid white pellet, rather than diluting it with water as mammals do.
The perentie is Australia’s largest lizard. It is a common species on Barrow Island, where it is one of the top predators.
The perentie shares the adaptations found in all reptiles, such as dry, relatively impermeable skin. It regulates its temperature by sheltering in underground burrows or in rock shelters, and basks in the sun to warm up in the early morning and late afternoon.
On very hot days, the perentie may seek shelter in the shade of vegetation or may climb a termite mound or shrub to get off the hot ground.

15. Other reptile examples
Thorny devil Tiny grooves over body direct moisture to the mouth Can change colour depending on temperature
Although reptiles are better adapted than many other species to hot, dry habitats, many reptiles show some unusual adaptations to living in these environments.
The thorny devil is an unusual-looking spiny lizard from Australia. It has tiny grooves all over its body that direct moisture to its mouth through capillary action. This allows it to collect water from morning dew or damp sand. The thorny devil can also change the colour of its skin, turning darker in cold weather to absorb heat better, and paler when warm.
The desert tortoise avoids hot summer conditions by becoming dormant, a process known as aestivation. This species lives in burrows and can survive for some time without drinking, obtaining most of the water it needs from its food. It can also store water in its large urinary bladder.
Desert tortoise Dormant during hottest part of summer (aestivation) Lives in burrows

16. Eastern sandfish Streamlined body allows it to ‘swim’ through sand
Saudi fringe-fingered lizard Fringes of elongated scales on the toes help in moving across sand
Many reptiles also show adaptations to moving across sand.
For example. the eastern sandfish has a streamlined body, very smooth scales and s chisel-shaped snout, giving it the ability to ‘swim’ through sand.
The Saudi fringe-fingered lizard has fringes of elongated scales on its toes which help it to move more easily across loose, shifting sand.
The sidewinder uses a unique ‘sidewinding’ motion across sand, with only two points on its body contacting the surface at any one time. This gives it more traction on loose sand and reduces contact between its body and the hot ground.
Sidewinder ‘Sidewinding’ movement across loose sand

17. Plants on Barrow Island
Spinifex grass (Triodia species) Extensive root system to collect water both from the surface and underground. Roots can be up to 3 metres long. Leaves have a waxy, impermeable surface (cuticle) to reduce water loss. Leaves curl inwards into long pointed tubes to slow the rate of transpiration.
Most of the landscape on Barrow Island is dominated by spinifex grasslands. Spinifex grasses have a number of adaptations to help them survive in a habitat with little water.
Spinifex grasses have an extensive root system to allow the plants to collect water both from the surface and deeper underground. These roots can be up to 3 metres long.
The leaves have a waxy cuticle on the surface through which water cannot pass, helping to reduce water loss.
The leaves of young spinifex plants are flat. However, during their first dry season the leaves curl or roll inwards, creating long pointed tubes. This reduces water loss as the stomata (pores) on the leaf surface through which water is lost are contained inside the tube, slowing the rate of transpiration (the process of water evaporating and diffusing out of the leaf).

18. Other plant examples
Grandidier’s baobab Stores water in trunk which can expand after rainfall
Lava cactus Stores water in thick stems, leaves reduced to spines to reduce transpiration
Bristlecone pine Parts of the living tissue die back during drought. Can still produce cones and seeds when conditions improve
Of course, different types of plants with different adaptations are found in arid habitats around the world. Here are some examples of the different ways plants cope in areas with little water.
Cacti like this lava cactus from the Galápagos can store water in their stems, and like spinifex grasses they also have a waxy cuticle. The leaves of cacti are reduced to spines, not only as to prevent them from being eaten, but also to give the minimum possible surface area for transpiration.
Trees such as Grandidier’s baobab from Madagascar are also able to store water in the fibrous wood of their trunks, and the diameter of the trunk contracts and expands with rainfall.
Bristlecone pines in the United States are among the oldest organisms on the planet; the oldest known tree was recorded at 4,789 years of age. These trees grow very slowly, and parts of the living tissue die back in times of drought, with only a small, sustainable part of the tree remaining alive. Although it may appear mostly dead, it can still produce cones and seeds when conditions improve.

19. Activity 1 You will be given a worksheet with a list of adaptations
species use to survive in arid habitats.
Your task is to decide whether each adaptation is a
behavioural or a physical adaptation.

20. Activity 1 - Answers Adaptation Behavioural? Physical? Being nocturnal
Impermeable skin
Producing concentrated urine
Aestivation
Panting
Ability to withstand high body temperatures
Seeking shade
Ability to store water inside the body
Light colouration
Living in a burrow
Large surface area
Leaves reduced to spine
Breed only after rainfall
Nasal counterflow
Go through the answers for the worksheet with the class.

21. Summary
Arid habitats are dry areas with little rainfall and are usually hot, although they can be cold at night.
Arid habitats cover over a third of the Earth’s land surface.
Animals and plants have evolved a range of adaptations to help them survive in arid habitats.
These adaptations can be behavioural, such as sheltering in a burrow during the heat of the day, or physical, such as having a large surface area to lose heat more quickly.
Run through a summary of what has been covered in the presentation, and they key points that have been learnt:
Arid habitats are dry areas with little rainfall and are usually hot, although they can be cold at night.
Arid habitats cover over a third of the Earth’s land surface.
Animals and plants have evolved a range of adaptations to help them survive in arid habitats.
These adaptations can be behavioural, such as sheltering in a burrow during the heat of the day, or physical, such as having a large surface area to lose heat more quickly.

22. Activity 2
The aim of this activity is to compare how effective different
adaptations are at helping a species to conserve water.
You will be given sponges soaked in water to
represent your arid “animals”.
You need to design an experiment to measure how much
water your sponges lose under various conditions set up to
represent different adaptations.
You need to weigh the sponges before and after the
experiment so that you can record how much weight
(water) each has lost.
Introduce the students to the second activity. Explain to them that their task is to design an experiment using sponges soaked in water to represent arid “animals”. These sponges are to be left in various conditions overnight, each of which represent a different adaptation. The sponges will be weighed at the start and at the end of the experiment in order to measure how much water each has lost, and therefore determine which of the “adaptations” was most effective. Further instructions are included on the activity handout.