Biology

Population size is affected by all of these factors and more. Birth rate, death rate, immigration, emigration, disease, competition and predation, human activity, natural disasters and occurrences. All of these are going to affect population size, but not all are involved in creating growth models. Next, we're going to look at population growth and the growth models that scientists use Remember, population size is the number of individuals in a group. This is different from population growth. We're going to talk about population. Growth Population growth is the change in the size of the group of organisms of the same species over time. This is determined by the birth rate, that is how many individuals are born into the group in one year? The death rate, how many individuals with that group have died that year? Immigration, how many new individuals entered the group from other groups? And emigration, how many individuals of that group left? This is described by the math formula that you're going to see on the slide. Birth rate plus immigration minus death rate plus emigration equal population growth. Remember if this number is positive, the population is growing. If this number is negative, the population is declining. So let's go through an example with these meerkats. Birth rate, right here, would refer to new babies that are born into the group. Let's call this guy and this guy a baby. So we have two babies. Immigration refers to new individuals who joined the group. We'll say that this guy is a newcomer into our meerkat group, so we have 1. Death rate refers to individuals in the group who've died. Let's say we had a serious predation issue in this group and we've lost 3. Minus 3 individuals obviously not pictured. Plus emigration, those would everybody who left the group for some new environment. We'll say 1 left in search of a mate. Now we're going to do our math and determine what our population growth for this set of meerkats is. 2 plus 1 is 3, minus 3 plus...