Back To CourseNational Board Certification Exam - Science/Adolescence & Young Adulthood: Practice & Study Guide
43 chapters | 405 lessons
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Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.
Let's learn a little bit about a bird called the dodo, which despite its unfortunate name wasn't actually stupid or goofy; it was just unlucky. Dodos lived on the island of Mauritius, which is east of Madagascar. Dodos were living quite happily on this island until humans arrived, and with them, animals like dogs and pigs. The poor dodo, being friendly and unassuming, was quickly hunted to extinction by these new predators (humans included), never to be seen again. The dodo was entirely eliminated, gone forever. What a shame!
Many animals go extinct because of human intervention like this, but extinction also occurs naturally. A species will go extinct when it can't adapt to the changing environment around it. That environment might include never-before-seen predators, changes in climate, availability of food resources, disease, or anything else that interferes with how that species normally interacted with its surroundings. Extinction may be the result of one factor changing, but because environments are dynamic, it's likely that a multitude of factors play into the loss of a species. Anything that prevents a species from producing more new individuals through reproduction than are lost through death will eventually result in the total loss of that species.
What's amazing is that almost all of the species that ever lived on Earth are now extinct -- 99.9% of them, in fact! Only a few have lived through either slowly occurring events or one of the five mass extinctions that each time wiped out more than 50% of the species that were on Earth at that time. So what's the big deal?
Well, first you'll notice that there have only been five mass extinctions during Earth's more than 4 billion years of existence. That means they don't happen very often and are very special events. The real trouble, though, is that everything in nature is connected to everything else, so if one species goes extinct, it has lasting effects on many other species. For example, you might not think that the disappearance of one species of bee is anything significant, but you can be sure that the plants pollinated by those bees and the animals that eat those bees as food would have something to say about it!
In other words, the extinction of just one species has a ripple effect, much like when you drop a stone into a pond. The stone may be quite small and you might not think it has much of an effect, but if you watch those ripples move outward, they eventually touch everything in that pond in some way. When we lose even one species the effect is the same within that ecosystem, and sometimes beyond it as well.
Unfortunately, extinctions caused by human intervention are more frequent than extinctions that would occur naturally. We're losing species at an alarming rate on Earth due to things like our mass destruction of forests, urbanization of wild landscapes, fragmentation of habitats, damming of rivers, introduction of foreign species, illegal poaching, overfishing, and more.
Humans are really good at interfering with nature for what we think is the greater good, but we often forget that nature has a pretty good system of checks and balances already in place. Take wolves, for example. Wolves are top predators that feed on things like deer and moose, but also smaller animals, like your friendly backyard raccoon. At one point wolves were hunted nearly to extinction in the U.S., which left very few predators to keep the prey populations in check.
Deer and elk populations especially grew out of control, and since there were more of them, that meant more plants were being eaten by them. The plants they were eating happened to be habitat and food sources for songbirds, which then suffered the consequences. And with fewer songbirds, fewer insects (like mosquitos!) were being eaten, and this led to an explosion in their populations. So from human intervention of just one species, all different kinds of plants and animals were affected, and ultimately so were we!
This is a lesson that should be taken to heart. We may not think that the species we are affecting affect us, but as you just saw and hopefully understand at this point, everything in nature is tied to everything else - even us.
Even with its unfortunate name, you might say that the real tragedy for the dodo was its untimely removal from Earth. As is more often the case than not these days, human intervention was the cause of this species' extinction, or entire elimination. Though we are highly influential in many extinctions these days, extinctions occur naturally from all sorts of environmental changes. Changes in habitat, climate, food and other resources, disease, new predators, or even new competition for the same resources: All of these are factors that may lead to individuals in a species dying faster than they can be replaced through reproduction.
Sometimes, though rarely, mass extinctions occur that remove over half of the species present on Earth at that time. There have only been five of these so far in Earth's history, and through these and smaller extinction events, a whopping 99.9% of all species that ever lived on Earth are long gone.
Humans are, unfortunately, fueling the extinction fire these days, far exceeding what would occur naturally without our help. Deforestation, habitat destruction and fragmentation, damming of rivers, urbanization, and even our purposeful interventions such as illegal poaching and hunting of top predators all have a ripple effect. All species on Earth are somehow connected to each other, so even the loss of one small species can eventually have large effects on others, including us.
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