Question

What is a mass extinction? Why do we think we are experiencing one now, and what are the factors causing this? The population density of one species can affect another. Understand why, and know examples. Understand the "birth-death" model of population change. In population growth, what is r?

Answer 1

1. What is a mass extinction?

Mass extinction is considered the disappearance of living beings from around the planet in a given time. This period can range from one year to several million years. It is believed that the earth has had five mass extinctions and that we are currently experiencing one.

2. Why do we think we are experiencing one now, and what are the factors causing this?

Several studies have indicated that we are currently going through the 6th mass extension caused exclusively by humans. To reach this conclusion has been investigated the number of living beings - plants and animals- which have been extinguished since the era of industrialization. For example, 322 vertebrate species have become extinct in the last five decades.

It is considered that what causes this mass extinction is the process of industrialization of the human being who has not been friendly to the environment for hundreds of years. For example, the use of fossil fuels has warmed the atmosphere preventing many animals from surviving the global temperature rise. Also, the human being has hunting until the extinction of diverse animals either for purposes of predation and even recreational purposes.

3. The population density of one species can affect another. Understand why, and know examples.

Ecosystems have a very delicate population balance where each species - Animal or plant - depends and interacts with each other. The population density of the species can negatively or positively affect the others. If the density affects negatively, it can break the balance of the ecosystem.

An example of negative population density could be the following;  

In an ecosystem where the population of toads is very dense and do not have predators (for example, there are no snakes that eat toads). Toads reproduce without control and decrease the number of insects (food of toads), and this will affect other animals that also feed on insects, such as birds.

4. Understand the "birth-death" model of population change.

The "birth-death" model of population change (named in honor of the mathematician Andrey Markov) describes how populations change over time. In biology, it is used to describe how species (considered populations) change over time through the evolutionary process. It is considered that when a species "dies," the evolutionary process results in the "birth" of two new species, unlike the extinction process where the species does not produce evolutionary descendants.

5. In population growth, what is r?

In the exponential growth formula of a population, r is considered to be the maximum growth rate of a population per individual, adding births and subtracting deaths in the population, based on the total population size.

This is the exponential growth formula of a population:

$\frac{dN}{dt} \frac{1}{N} = r$

I hope this information can help you. Have a nice day.