Population Growth and Limiting Factors

What factors increase population size? Two factors can increase the size of a population, birth and immigration. Two factors can decrease the size of a population, death and emigration. What does line K mean? This is the number of individuals a given area can support This is the number of individuals born every year This is the number of individuals that leave an area every year Which line shows logistic growth? A B K For the growth curve to continue increasing, which of these must occur? The organisms must adapt to a new habitat The organisms must migrate to a new environment The resources in the environment must be unlimited The environment must must have a limited amount of food Exponential Growth Has a "J" shaped curve can only occur when there are unlimited resources availalbe Logistic Growth Has a period of rapid growth followed by the population leveling off Population runs out of resources and hits its carrying capacity Caused by limiting fators Has an "S" shaped curve Type of Limiting FactorsRead the information below to help you with the questions (from KhanAcademy) Density-dependent limiting factorsLet's start off with an example. Imagine a population of organisms—let's say, deer—with access to a fixed, constant amount of food. When the population is small, the limited amount of food will be plenty for everyone. But, when the population gets large enough, the limited amount of food may no longer be sufficient, leading to competition among the deer. Because of the competition, some deer may die of starvation or fail to have offspring, decreasing the —growth rate and causing population size to plateau or shrink.In this scenario, competition for food is a density-dependent limiting factor. In general, we define density-dependent limiting factors as factors that affect the growth rate of a population differently depending on how dense the population already is. Most density-dependent factors make the growth rate go down as the population increases. This is an example of negative feedback that limits population growth.Density-dependent limiting factors can lead to alogistic patternof growth, in which a population's size levels off at an environmentally determined maximum called thecarrying capacity. Sometimes this is a smooth process; in other cases, though, the population may overshoot carrying capacity and be brought back down by density-dependent factors.Density-dependent limiting factors tend to bebiotic—living organism-related—as opposed to physical features of the environment. Some common examples of density-dependent limiting factors include:-Competition within the population. When a population reaches a high density, there are more individuals trying to use the same quantity of resources. This can lead to competition for food, water, shelter, mates, light, and other resources needed for survival and reproduction.-Predation. Higher-density populations may attract predators who wouldn’t bother with a sparser population. When these predators eat individuals from the population, they decrease its numbers but may increase their own. This can produce interesting, cyclical patterns, as we'll see below.-Disease and parasites. Disease is more likely to break out and result in deaths when more individuals are living together in the same place. Parasites are also more likely to spread under these conditions.-Waste accumulation. High population densities can lead to the accumulation of harmful waste products that kill individuals or impair reproduction, reducing the population’s growth.Density-independent limiting factorsThe second group of limiting factors consists of density-independent limiting factors that affect growth rate independentof how dense the population is.Image of a forest fire with elk standing in a river for safety.Image credit:Elk bathby John McColgan, USDA, public domainAs an example, let's consider a wildfire that breaks out in a forest where deer live. The fire will kill any unlucky deer that are present, regardless of population size. An individual deer's chance of dying doesn't depend at all on how many other deer are around. Density-independent limiting factors often take the form of natural disasters, severe weather, and pollution.Unlike density-dependent limiting factors, density-independent limiting factors alone can’t keep a population at constant levels. That’s because their strength doesn’t depend on the size of the population, so they don’t make a "correction" when the population size gets too large. Instead, they may lead to erratic, abrupt shifts in population size. Small populations may be at risk of getting wiped out by sporadic, density-independent events. Types of Growth and Limiting Factors Density Dependent Limiting Factor Type of limiting factor that has a greater effect the larger a population gets Density Independent Limiting Factor Type of limiting factor that has the same effect regardless of population size Separate the limiting factors into density dependent and density independent limiting factors: Density Dependent Limiting Factors Predation Disease Food supply Shelter Density Independent Limiting Factors Human activities such as deforestation Unusual weather patterns Natural Disasters