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Population Ecology-J Curve, S curve and Age Distribution !! POPULATION A group of organisms of the same species occupying a particular space at a particular time. POPULATION ECOLOGY Population ecology is a study of populations in relation to the environment. It deals with the factors that influence the population’s size, growth, density, distribution, age structure and many other features. DENSITY AND DISPERSION DENSITY: IS the number of individuals per unit area or volume. DISPERSION: is the pattern of spacing among individuals within the boundaries of the population. POPULATION SIZE Population size depends on a balance between NATALITY=Birth Rate (b) MORTALITY=Death Rate (d) If birth rate (b)>death rate (d) —- r is (+); population is increasing in size. If (b) < (d) —–r is (-); population is shrinking. If (b) = (d) —–r is (0); population size is constant. Besides natality and mortality, population size also depends on the movement of individuals between population s (migration) IMMIGRATION RATE (i)=movement of individuals into a population EMIGRATION RATE (e)=movement of individuals out of a population. FACTORS THAT AFFECT FUTURE POPULATION GROWTH POPULATION GROWTH Two factors influence the dynamics of a population BIOTIC POTENTIAL: Promotes positive growth intrinsic factors(litter size, gestation period) ENVIRONMENTAL RESISTANCE: Limits growth extrinsic factors(weather, food supply etc. ) PATTERNS OF POPULATION GROWTH 1. EXPONENTIAL GROWTH: Exponential population growth is population increase under idealized condition Under this condition the rate of reproduction is at its maximum, called the intrinsic rate of increase. The equation of exponential growth is J-shaped curve of exponential population growth is a characteristics of some population that are rebounding. Exponential growth can not be sustained for long in any population. A more realistic population model limits growth by incorporating carrying capacity Carrying capacity (k) is the maximum population size the environment can support. LOGISTIC GROWTH: 2. In the logistic population growth model the per capita rate of increase declines as carrying capacity is reached. The logistic growth equation includes k,the carrying capacity What limits population size around carrying capacity? 1. DENSITY DEPENDENT FACTORS: Competition(habitat space, food resource, mates) Disease Predation 2. DENSITY INDEPENDENT FACTORS: Weather condition Catastrophes Natural disasters SURVIVORSHIP CURVES 1. A survivorship curve traces the decline of a group of new borns over time. 2. Survivorship curve plot the probability of surviving to a certain age for a representative member of the population. TYPES OF SURVIVORSHIP CURVES 1. TYPE I; CONVEX CURVE: Most individuals live to adulthood with most mortality occurring during old age.(i.e., humans red deer, elephants) 2. TYPE II; STRAIGHT LINE: An individual’s chance of dying is independent of its age (i.e., small birds, mammals) 3. TYPE III; CONCAVE CURVE: Few individuals lives to adulthood, with the chance of dying decreasing with age.(i.e., oysters, red wood trees, snapping turtles) AGE DISTRIBUTION 1. The age distribution of a population is the portion of individuals at different ages. 2. It has a significant impact on future population growth. 3. Population that have remained constant for a long time have stable age distribution, which reflect an individual’s chance of living a given amount of time. 4. Rapidly growing populations will have disproportionate number of young individuals. POPULATION PYRAMIDS A population pyramid is also called an age pyramid or age picture diagram. It is a graphical illustration that shows the age distribution of various age groups in a population. TYPES OF POPULATION AGE PYRAMIDS Population age pyramid has mainly four types. 1. STABLE PYRAMID: a population pyramid showing unchanging pattern of fertility and mortality. an 2. STATIONARY PYRAMID: a population pyramid typical of countries with low fertility and low mortality. 3. EXPANSIVE PYRAMID: a population pyramid that is very wide at the base, indicating high birth and death rates. 4. CONSTRICTIVE PYRAMID: a population pyramid that comes in at the bottom. the population is generally older on average, as the country has long life expectancy a low death rate, but also a low birth rate. THIS IS THE GENERAL IDEA OF POPULATION ECOLOGY. If you want our reguler updates, please follow us on facebook , G+, tweeter and others. Share this post to your friends. Thank You.