Recording one
Governments private groups and individuals spend billions of dollars a year trying to root out non-native organisms that are considered dangerous to ecosystems and to prevent the introduction of new intruders.
But a number of scientists questioned the assumption that the presence of alien species can never be acceptable in a natural ecosystem.
They say that portraying introduced species as inherently bad is an unscientific approach.
Distinctions between exotic and native species are artificial said Dr Michael Rosen xv eek a professor of evolutionary biology at the university of Arizona.
Because they depend on picking a date and calling the plants and animals that show up after that date exotic.
Ecosystems free of species defined as exotic are by default considered the most natural.
You can't roll back the clock and remove all exotics or fix habitats, dr. Rosen speak said both native and exotic species can become invasive and so they all have to be monitored and controlled when they begin to get out of hand.
At its core the debate is about how to manage the world's remaining natural ecosystems and about how and how much to restore other habitats.
Species that invade a territory can harm ecosystems agriculture and human health, they can threaten some native species or even destroy and replace others next to habitat loss, these invasive species represent the greatest threat to biodiversity worldwide, many ecologists say.
Ecologists generally define an alien species as one that people accidentally or deliberately carried to its new location.
Across the American continents exotic species are those introduced after the first European contact.
That date rounded off to fifteen hundred ad represents what ecologists consider to have been a major shift in the spread of species including crops and livestock as they began to migrate with humans from continent to continent.
Only a small percentage of alien species cause problems in their new habitats said Don Smith professor of ecology and evolutionary biology at the university of Tennessee.
Of the 7000 alien species in the United States out of a total of 150,000 species, only about 10% are invasive, he pointed out.
The other 90% have fit into their environments and are considered naturalized.
Yet appearances can deceive ecologists, caution and many of these exotics may be considered acceptable only because no one has documented their harmful effects, what is more non-native species can appear harmless for decades, then turn invasive.
Questions sixteen to eighteen are based on the recording, you have just heard
- Questions sixteen
what assumption about introduced species is challenged by a number of scientists. - Question seventeen
what does dr. Michael Rosen's wiig, think of exotic and native species. - Question eighteen
What does professor Don Smith say about alien species.
Listen to part of a lecture in a psychology class.
We've said that the term cognition refers to mental states like knowing and believing and to mental processes that we use to arrive at those states, so for example reasoning is a cognitive process so as perception, we use information that we perceive through our senses to help us make decisions to arrive at beliefs and so on, and then there are memory and imagination, which relate to the knowledge of things that happened in the past or may happen in the future, so perceiving remembering imagining are all internal mental processes that lead to knowing or believing yet each of these processes has limitations and can lead us to hold mistaken beliefs or make false predictions take memory for example, maybe you've heard of studies in which people here a list of related words, let's say a list of different kinds of fruit after hearing this list.
They're presented with several additional words in this case, we'll say the additional words were blanket and neither of these words was on the original list, and while people will claim correctly that blanket was not on the original list, they'll also claim incorrectly that the word was on the list, most people are convinced they heard the word on the original list and why do they make such a simple mistake, well we think because the words on the list were so closely related the brain stored only the gist of what it heard, for example that all the items on the list were types of fruit when we tap our memory our brains often fill in details and quite often these details are actually false.
We also see this fill-in phenomenon with perception.
Perception is the faculty that allows us to process information in the present, as we take it in VIA our senses again, studies have shown that people will fill in information that they thought they perceived even when they didn't, for example experiments have been done where a person hears a sentence but it's missing the word that logically completes it they'll claim to hear that word even though it was never said so if I were to say, um, the sun rises in the and then fail to complete the sentence, people will often claim to have heard the word east.
In cognitive psychology, we have a phrase for this kind of inaccurate filling in of details, it's called a blind spot, the term originally referred to the place in our eyes where the optic nerve connects the back of the eye to the brain, there are no photo receptors in the area where the nerve connects to the eye so that particular area of the eye is incapable of detecting images, it produces a blind spot in our field of vision, we are aware of it because the brain fills in what it thinks belongs in the image, so the picture always appears complete to us, but the term blind spot has also taken on a more general meaning, it refers to people being unaware of a bias that may affect their judgment about a subject and the same blind spot phenomenon that affects memory and perception also affects imagination, imagination is a faculty that some people use to anticipate future events in their lives, but the ease.
Which we imagine details can lead to unrealistic expectations and can bias our decisions, so um, Peter suppose I ask you to imagine a lunch salad, no problem right, but I bet you imagine specific ingredients did yours have tomatoes onion lettuce.
Minded our brains fill in all sorts of details that might not be part of other people's image of a salad which could lead to disappointment for us, if the next time we order a salad in a restaurant, we have our imagined salad in mind, that's not necessarily what will get on our plate, the problem's not that we imagined things but that we assume what we've imagined is accurate, we should be aware that our imagination has this built-in feature, the blind spot, which makes our predictions fall short of reality.