Tuesday, February 22, 2011

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ECOLOGY OF POPULATION: population dynamics, logistic and exponential curve.


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Una popolazione è costituita da individui conspecifici (della stessa specie) che vivono all'interno di un area ben definita, in un determinato periodo di tempo e che condividono, nell'ambiente che occupano, lo stesso ruolo funzionale (

). Una popolazione è regolata da due meccanismi fondamentali, il primo è la nutrizione, può fungere from limiting factor for growth of a population such as when the amount of nutrients in an environment is severely restricted, and the second is the reproduction, which is a multiplier. The main characteristics by which this population are: a) population size
:
namely the total number of individuals who compose it.
b)
age distribution: The number of individuals or the percentages that make up each class.
c)
spatial dispersion: shows us how the population is dispersed in the environment.
Dynamics of the population.

There are parameters that allow the study of changes in the size of a population, its age distribution and its dispersion, and these benchmarks are
birth (which allows us to determine the number of children produced, on average, for every Everyone over a certain period of time), the mortality
(which allows us to determine the number of individuals who die on average over a certain period of time);
immigration and emigration . The concept of the birth rate can be divided into: births maximum (absolute or physiological) would represent the birth theoretical maximum of new individuals in the absence of limiting conditions.
births real or ecological:
birth conditions. Example: pettirssi produces a population of 510 eggs, so the theoretical birth of 510 individuals, but ultimately there's only 265 eggs to hatch and mature. 265:510 = x: 100. the birth of the label is x = 52%
mortality: contrast the birth rate in this case too we have a theoretical minimum
mortality: number of deaths in ideal conditions and not limiting, then the organisms die just because of old age not by other factors.
Mortality real or ecological:
loss of individuals due to an environmental factor.
exponential growth.
In theory, the birth rate of a population is always much higher than the true value. After all if we think about the number of acorns produced by an oak tree during its life is enormous and yet not all generate a tree in the human species could also have a fertile female from 20 to 30 pregnancies (excluding twin births), but not always the case. In general, as pointed out by Malthus (1798) populations have the potential to grow exponentially. Growth is described by the equation:
ΔN / Dt = B - N

where N / t indicates the change in population in given period of time; B indicates the number of births during the interval, N the deaths during the time interval .
The equation can also be described by the formula
dN / dt = r - N
where r is a constant that intrinsic rate of population growth under optimal conditions, r in a nutshell is the difference between birth rate and mortality.
course in a natural population increase ever in the Info is not because its growth is determined and influenced by many factors including the nutritional resources such that are never available indefinitely without counting the influence that factors such as availability of space, the number and type of organisms present in the environment and the various relationships that develop between them (predation, competition, parasitism, etc. ...).
intraspecific competition and logistic curve.

In fact, because of the increasing density of population of individuals who have very similar ecological requirements for survival, growth and reproduction, interact increasingly subtracting the environment, and other members of the population of the available resources. So an increasing number of individuals in a population causes a decrease in increasing the resources available, so there is a limit to the number of individuals an environment can accommodate, this has serious repercussions for the ability to reproduce.

picture on the side you can see an example of logistic growth model. With K indicates the carrying capacity of the environment,
ie the maximum number of individuals in a population that a given environment can support, which in turn depends on the resources available is a value that tends to vary in time and space. The rate of growth slows to just recently that the population approaches the carrying capacity of the system. The red curve shows the logistic growth of the population. The point where the black (K) and the red face represents a value of N where the population does not increase it decreases, a point of stable equilibrium. Remember that when we speak of load bearing habitat mean the biotic and abiotic components of an environment in which the population lives, the habitat of a community is different, only includes the abiotic characteristics. When the population tends to K the growth rate tends to zero, because diminishing resources increases mortality, migration, fertility is reduced and so on. The curve logistics as shown in the chart formuletta (in red) corresponds to the equation:
dN / dt = r N (KN / K) Not all parameters affecting the growth of a population is density dependent (even though most are). For example, exceptionally low or high temperatures can kill some of the independent body the density. Thus the increased resources of a population decline, this will cause the death of many individuals and lead to a decrease in density resulting in increased resources and the population grows in number. Obviously other factors come into play more, such as increase in population also means an increase of predators, however, decrease of food resources (due to high density of herbivores, for example) will cause a decrease in the growth of the latter and eventually will have fewer predators herbivores to hunt and even then their number will decrease allowing the population to grow again.
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