Good examples include the eucalypts, banksias, and heath plants endemic to Australia. One such set of adaptations is referred to as scleromorphy characterised by hard and relatively small, thick leaves. Only sufficiently specialized plants can survive in such nutrient deficient soils. According to the Australian Academy of Science, “this weathering has dissolved vast quantities of nutrients, and washed them away into the groundwater and/or rivers, leaving the soils depleted in nutrients such as phosphorous, calcium and potassium.” Ice sheets never advanced over the continent, so the soils are very old, having undergone weathering and erosion over many thousands of years. In Australia, most of the land mass was never glaciated. This helps explain the rich soils of the North American plains, for example. As the newly exposed rocks weathered, nutrient rich soils were deposited on top of the bedrock. In much of the world, the continents were covered in ice sheets during the last ice age, which scraped away the soil as they moved over the continents. But there’s much more – let’s talk ice (or lack of ice!) These trends offer a partial explanation for the low levels of nutrients present in Australian soils. Over the past 50,000 years Australia has steadily become drier due to natural climate change and human modification of the environment through burning and hunting. How Did the Koala Evolve To Have a Shrunken Brain? What does a shrunken brain have to do with poor soil? Australia’s poor soils are where t he story of the Koala’s reduced brainpower begins. Thankfully, they can learn to take advantage of underpasses designed to facilitate wildlife travel (see details at the end of this article).Īnother major threat to koalas is the escalation in bush fires throughout Australia because of human-caused global warming. Mortality rates are high close to populated areas. Sadly, they don’t seem able to adapt very well to moving cars or the dangers of crossing highways. They move slowly and deliberately from sleeping spot to food source and back again. They expend as little energy as possible, spending roughly 18-20 hours per day sleeping. Let’s be honest koalas are not too bright. Looks like this koala fell asleep in the middle of doing something important! Tim Flannery, one of Australia’s leading scientists, is not too flattering about a koala’s brain! He writes, “Its hemispheres sit like a pair of shriveled walnut halves on top of the brain stem, in contact neither with each other nor the bones of the skull.” Koalas might be cute, but what’s inside the skull doesn’t sound very impressive. Many researchers believe that the ancestors of the modern-day koala once had a full-sized brain that filled the cranium. Nevertheless, there is no doubt that marsupials show low encephalization in comparison with eutherians (Martin 1990 De Miguel and Henneberg 1998).” Taylor et al. Data presented here fit better into known encephalization data for other marsupials and eutherians (Tobias 1971 Martin 1990). It may be a result of studying a live animal and a fresh dead one, rather than chemically preserved brains. “The ratio of total brain volume – including olfactory bulb – to the endocranial volume is remarkably larger than previously reported (Haight and Nelson 1987) and closer though still larger than what De Miguel and Henneberg (1998) found. (Eutherians refers to all the mammals that have a placenta that is, all mammals except monotremes and marsupials.) More recent studies show that the Koala’s brain probably fills about 70-75% of the brain cavity. It was thought that the koala’s brain only filled 60% of the brain cavity. “Given the inconsistency of encephalization indices and animal lifestyles and behaviour, one can wonder what we can learn from encephalization quotients.” (de Miguel and Henneberg, 1998) Scientists often use the ratio of brain volume to body mass or total brain volume to endocranial volume when they present encephalization data. Research on the Koala’s brain is ongoing. Using the least amount of energy possible appears to be a key adaptation to surviving on a nutritionally poor, low energy diet of toxic eucalyptus leaves. Even though koalas are dumb, they have survived because their brains use minimal energy. The koala has one of the lowest ratios of brain to body mass of any mammal. Even though it is becoming more and more difficult to see wild koalas in their native habitat, we have managed to track them down by following the amazing roars of the male. Whenever we travel to Australia, we love to observe that iconic marsupial, the koala (Phascolarctos cinereus).
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |