Dinâmica de populações

#Biology #Ecology #PopulationDynamics Class aimed at high school and ENEM students on population dynamics. Video Script: First, let's define a population, which is a set of species that inhabit the same environment at the same time. So, to begin working with population dynamics, we must first understand that there is a population density, that is, the number of individuals of a given species relative to the size of the area it occupies. For example, the population density in the Amazon is 2.66 inhabitants/km2, while in São Paulo it is 184.99 inhabitants/km2. In other words, we have many more people per meter in São Paulo than in the Amazon. Once we have defined density, we can now study how this density will vary over time, but to do so, we must consider some concepts. Birth rate - Number of births in a given unit of time. Mortality rate - Number of deaths in a given unit of time. Immigration rate - Number of individuals entering the population per unit of time. Emigration rate - Number of individuals leaving the population per unit of time. Another very important concept is biotic potential, which is the capacity of a natural population to grow in favorable environments, that is, without the addition of any planned impacts. Environmental resistance is the opposition to biotic potential. Resistance will prevent the biotic potential from developing a very large population. The greater the potential, the greater the resistance. This resistance is characterized by food, climate, space, competition with other organisms, predation, etc. So, we can say that in a normal population, we have a normal growth curve over time. That is, once the population is introduced into the environment, it will go through a phase of slow growth, which is the time during which the organisms will adapt to the new environment. Once adapted, they will begin to reproduce, then we have the phase of rapid growth, where the birth rate and emigration become very high. Then, due to environmental resistance, we have the phase of stunted growth. After this, if everything proceeds naturally, the population reaches a dynamic equilibrium, where there is a small variation in numbers, but it always remains around an average number of individuals. These fluctuations are a consequence of interactions with other organisms and the environment. Within these influences, we have some main ones, such as intraspecific competition (with individuals of the same species) or interspecific competition (with other species), which will cause changes in both populations. We also have predation. Normally, if the prey population increases, the hunters feed more and increase their population. With more predators eating, the prey population begins to decline. At this point, the hunters run out of food, and their population subsequently declines. With the decline in predator numbers, the prey numbers increase again, and then the predators increase due to this increase, and the cycle continues. Diseases can also have some impact, such as pandemics and epidemics of some parasitic agent. In this case, I suggest watching the lesson here on the channel on the subject. We also have climatic factors, such as light, temperature, humidity, etc. These can cause some kind of change depending on how the organism is adapted to different environments. You've probably heard that global warming has caused many animal deaths, just by increasing the temperature by 2 degrees. And the last thing that can influence it is diet, which, after all, basically serves as predation. The greater the food supply, the larger the population size. When food begins to be eaten too much and becomes scarce, the population declines, and so on. Another interesting point is who regulates population growth: diet or predation? If this population is controlled by the predator, that is, the larger the population, the more predators there will be and this will cause pressure for the population to decrease, in the so-called Top-Down effect, now if the control is done by food, since the larger the population, the greater the amount of food consumed, and when this food becomes scarce it will cause the population to decrease, we call this effect Bottom-Up.