5.1 Text - Growth Curves

Main Ideas:

The textbook pages that should have been read over the weekend were sections 5.1 and 5.2. In section 5.1, the book described how to read a “J-Curve” graph. It shows the point where the growth is of the highest rate, and it shows how the higher the population, the faster it will grow. The J-Curve shows how a population increases in a certain habitat, and gives you an idea of how the species survives in the habitat. Another name for the J-Curve is called Exponential Growth.

Key Point: under ideal conditions with unlimited resources, a population will grow exponentially.

Another important graph that was reviewed was the “S-Graph”, also known as the Logistic Growth. This graph shows phases 1, 2, and 3 of the growth of a population. The first phase shows the population growing rapidly, the second shows the slowing curve of the population growth, and the third phase shows the complete halt of population growth. The third phase shows the carrying capacity. The carrying capacity is the maximum number of individuals of a particular species that a particular environment can support.

Key Point: logistic growth occurs when a population’s growth slows and then stops, following a period of exponential growth.

Things of importance:

A population’s allocation in a specific environment can vary, too. Some environments will have sparsely populated inhabitants, while others will be closed concentrations of species, dotted along the specific environment. Some species are allocated in their environment randomly, so they can be all over the place. Another type of allocation of a species is uniform, where the species will be populated accordingly, and neatly, so there is no overcrowding. Most commonly, a species will be clumped together for purposes including safety, shelter, and resources.

The area inhabited by a population is called its geographic range. These areas are entirely controlled by that species, and its range extends until the area that is not inhabited by that species is found. For example, a bacterial population in a rotting pumpkin may have a range smaller than a cubic meter.

The growth rate of a population determines whether the population increases, decreases, or stays the same. Species that are in their original or natural habitats often have the same population over time. These populations have a growth rate close to zero. Populations can also decrease in size, depending on the habitat that they are in. That specific population would have a negative growth rate.

Limiting factors can also be introduced into an environment that ultimately limits the population of a certain species. A limiting factor could be things like predation, parasitism, and disease. These limiting factors do depend on the population density though. If there is a shortage of prey for predators, the predators will starve, and most likely die of starvation. If it was the opposite, and there was more prey than there are predators, than the predator’s population will most likely grow, making an onward cycle. These limiting factors are very important to control a fast growing population. These limiting factors are density-dependent.

Density-independent limiting factors affect all populations in similar ways, regardless of population size and density. Things like monsoons, hurricanes, tornadoes, or earthquakes will happen no matter what, and do not depend on the size of a population in that specific environment. In such events, populations will “crash”, and the population will fall rapidly. After the crash, a population will grow rapidly because there is an abundance of food and shelter, considering there is less of a population of that species than there was before.

All of this information can be found on pages 130-140 in the textbook. Do it if you haven’t done it, or else.