Biological Diversity Flashcards

Question

Account fir the changes in prickly pear distribution in Australia over time

Answer 1

Prickly pear can reproduce from seed or pads (small pieces of tissue that have broken off). The climate in parts of inland Queensland and northern NSW is similar to the prickly pear's place of origin. Birds can spread the seed after eating the prickly pear's fruit. These factors, combined with a lack of selection pressures found in the original ecosystem, meant that prickly pear initially had exponential growth and a sustained population explosion shortly after its introduction to Australia. The abundance of prickly pear caused great hardship for farmers in these areas until 1926 when a biological control was introduced. The cactus moth (Cactoblastis cactorum) was brought to Australia from South America. The moth lays eggs in the prickly pear tissue and the larvae that hatch feed on and often destroy the plant. Within six years, the moth had greatly reduced the prickly pear population. The prickly pear has persisted in the cooler regions of its previous range because the cactus moth does not thrive in a cooler climate.

Answer 2

The many Galápagos finch species are an example of divergent evolution. Populations of a once widespread finch species have adapted to different selection pressures on different islands. Over time, the finches on each island have become increasingly divergent (different), eventually becoming different species.

Answer 3

After his return to England, Darwin did further study of the finch specimens he had collected from the Galápagos Islands. It became clear to him that the finches were closely related but had evolved into different species. He was able to link the beak structure of each finch species to the type of food available on the island where it was collected. Using this evidence, he surmised that natural selection had been at work––those individuals that were best-suited to their environment survived and produced the most offspring, passing on their beneficial traits to the next generation. When the ancestral finch species arrived and settled on each different island any individuals that happened to have beaks more suitable to gather the food available on that island were the ones to survive. These successful individuals reproduced and passed their genetic variation for beak shape to their offspring. Over many generations, the well- adapted beak shape became more common in the population because these individuals were better adapted to survive and reproduce. Eventually the birds on different islands with different types of food (e.g. small tough seeds compared to large soft fruit) evolved into different species.

Answer 4

A transitional series of fossils provides a comprehensive record of microevolutionary changes as the organism accumulates differences over many generations. For example, the earliest ancestors of the modern horse were much smaller, browsed on soft leaves and fruit in rainforests and had five toes with soft pads on each foot. Teeth preserve well as fossils and tell the story of diet and age for an organism. The fossil record shows that horses evolved to become taller, stronger and have hard hooves and much tougher teeth for grinding coarse grass. The environment had changed over time from rainforest to open grassland and this selected for the horses that could graze on grass and run fast to escape predators in the open. Many fossils have been found that document these changes in small steps for horse species. Punctuated equilibrium is a later modification to Darwin’s original theory that described gradual evolution by natural selection. It explains periods of stability for well-adapted organisms with no or little evolutionary change unless their environment changes suddenly. A sudden change in natural selection pressures causes emigration, extinction or relatively rapid evolutionary change in the population of organisms. Their fossil record will show punctuations (sudden changes) in the equilibrium of stability. In the horse fossil record, the evolution of high-crowned teeth appeared quite suddenly and reflects a transition from browsing to grazing on grass as climate change favoured grassland rather than rainforest and woodland. At this time, several species of horse became extinct. Only one line survived and it later diverged into some taller, faster, grazing species. Of these, only the Equus genus survives today. Punctuated equilibrium differs from gradualism that refers to slow, steady evolutionary changes. With the advantage of a complete transitional series of fossils, the rate of change can be deduced.

Answer 5

Uranium–lead dating is used for very old samples of rock such as this one because uranium-238 has a half-life of 4500 million years. Carbon-14 has a much shorter half-life (5730 years), making it useful for dating organic specimens up to 50 000 years old. The rock sample is much older than the carbon dating range and is more likely to contain uranium-238 than carbon-14 atoms.

Answer 6

Fossil records provide ample evidence of extinctions having occurred throughout the long history of life on Earth. Dinosaur fossil remains are plentiful, there are many on public display and it is apparent from reliable dating that most dinosaurs did not survive the end of the Cretaceous (66 mya) when there was a mass extinction event. Pterosaurs also became extinct at this time. There are many earlier and later examples in fossil form such as the numerous trilobites, none of which survived later than 240 mya. Many recent extinctions can be attributed to human impact. Hunting and habitat destruction are two of the main causes.