Famine and Fate

If a population of bacteria is grown in the laboratory under totally optimal conditions and with unlimited resources, it will grow at its maximum rate, which can be as much as one doubling of the population every half hour. This is called the biotic potential. If just one resource becomes limiting or the population runs into space problems (crowding), it may collapse either immediately or more slowly. However, in nature there are almost always one or several conditions that are not optimal - even not suboptimal. Therefore, it is not common for a population in nature to grow at its biotic potential. It may happen over short periods of time, if for example an invasive species enters a system where there is plenty of food and space because the invader is a better competitor than the native species. Another example would be the introduction of a predator into a system with a large prey population. However, neither of the above situations would last for long, since the intruder populations will limit themselves (shading, overcrowding, parasitism, etc.) or because the indigenous population dynamics may change in a direction which is not beneficial for the intruder (Figure 1).

Months

Figure 1 Seasonal variation in population biomasses of major plankton populations in a nutrient-rich temperate lake. Phytoplankton growth is stimulated by increasing light attenuation in the early spring while exhausting of nutrients and grazing by zooplankton will diminish the biomass later on. The heterotrophic populations (i.e., bacteria, protozoa, rotifers, and zooplankton) are controlled by temperature, food, and predation from fish (directly or indirectly).

Months

Figure 1 Seasonal variation in population biomasses of major plankton populations in a nutrient-rich temperate lake. Phytoplankton growth is stimulated by increasing light attenuation in the early spring while exhausting of nutrients and grazing by zooplankton will diminish the biomass later on. The heterotrophic populations (i.e., bacteria, protozoa, rotifers, and zooplankton) are controlled by temperature, food, and predation from fish (directly or indirectly).

The study of how a species population interacts with the environment and its resulting dynamics is often referred to as autecology; synecology (or community ecology) refers to the study of groups of organisms in relation to their environment. A number of factors can stimulate or limit a population's growth, and some of these factors depend on the population's density. The most common density-dependent factor that limit population growth rates is availability of food. This includes both the amount of food that is edible (i.e., within the size range that can be handled by a given consumer) and the energetic quality of the food. The metabolic requirement of a population is related to the actual size of the organisms as well as the age structure of the population. Small organisms need more food per unit biomass due to a high surface to volume ratio. Species that have overlapping food size spectra would clearly compete with each other for food and the outcome may be that the realized food availability is less than it would be without competitors.

Another important factor is light, as it is an obvious resource needed for autotrophic organisms such as phy-toplankton and submerged water plants. The light intensities vary considerably over the season, among climate zones and with depth of the water body. For the same reason the light requirements differ widely among phototrophs, and the depth limit where rooted plants can grow may range from a few meters up to 100 m. Very strong light intensities can have a limiting effect on photosynthesis by inhibiting the enzymatic processes.

Many other factors such as temperature, pH, oxygen concentration, inorganic and organic nutrients are necessary for many living creatures. Yet other constituents of aquatic ecosystems, which affect the growth and decline of plankton populations are parasites, fungi, and diseases. These factors can limit the population's performance; the outcome is often that death rates equal birth rates and thus the population size reaches a stable stage.

The overall implication of the limiting factors that act upon a given population is that the abundances (or biomasses) of specific populations vary considerably in time and space and among ecosystems (Table 2). Many species have developed strategies such as migration, diapause, and resting eggs to survive unsuitable times or spaces.

Solar Power Sensation V2

Solar Power Sensation V2

This is a product all about solar power. Within this product you will get 24 videos, 5 guides, reviews and much more. This product is great for affiliate marketers who is trying to market products all about alternative energy.

Get My Free Ebook


Post a comment