Characteristics Of Populations 4k2g70

Characteristics of Populations 1.

a) The three different measurements that scientists use to describe populations are population sizes, population densities and population dispersion or spacing. b) The population size is the number of individuals in a population while a population density is the number of individuals per unit or volume.

2. a) Crude density includes all the land within the organisms range whereas ecological density includes only that portion of a land that can actually be colonized by the species. b) 3. Population dispersion is the pattern of spacing among individuals within the geographic boundaries of the population. 4. a) A clumped dispersion pattern is the most common pattern of dispersion with individuals aggregated in patches. For example mushrooms are often on a rotting log. b) A uniform dispersion pattern or evenly spaces may result from direct interactions between individuals in the population. It may due to shading and competition. For example are birds such as penguins. c) Random dispersion pattern is the rarest in nature which occurs in absence of strong attractions or repulsions among individuals of a population; the position of each individual is independent of other individuals. For example are trees in a forest and a population of bacteria are often randomly distributed.

d) There are many factors that determine the spacing between organisms in a population. But the main reasons of dispersion are not all areas are provided equally with suitable habitat, individuals exhibit patterns of spacing in relation to other of the population and the nutrients and food are not properly distributed in an area. e) Random dispersion pattern is relatively rare in nature because it is unlikely for organisms to have an absence of strong attractions or repulsions to one another. Also, most organisms are dependent one another and their food which always result to clumped and uniform distribution patterns. Measuring and Modeling Population Change 1.

a) The term, “environment,” refers to the surroundings of an object. It is the physical and biological factors along with their chemical interactions that affect the organisms in a population.

b) At any one time, many organisms are limited in their local distributions by the presence of biotic factors such as food resources, predators, diseases and competitors. c) At any one time, many organisms are limited in their local distributions by the presence of abiotic factors such as temperature, water, light and wind- the major components of climate. Temperature and water are especially important factors in determining the geographic range of organisms. 2.

a) Ecologists define carrying capacity as the maximum population size that a particular environment can at a particular time. b) c) Energy limitation is one of the most significant determinants of carrying capacity along with the shelters, refugees from predators, soil nutrients, water and suitable nesting and roosting sites. d) Crowding and resource limitation can have a profound effect on the population growth rate. As a population increases in size, each individual has an access to an increasingly smaller share and an increase in competition rate.

3.

a) The term, “population dynamics” refers to the aggregate of processes that determine the size and composition of any population. It is the aspect of population ecology dealing with forces affecting changes in population densities or affecting the form of population growth. b) A population can increase in size if birth rate is higher that death rate and if immigration is higher than emigration. c) On the other hand, a population can decline in size if death rate is higher than birth rate due to external forces such as diseases or natural disasters. As well, if emigration is higher than immigration. d) Natality is the ratio of the number of births to the size of population; birth rate. Mortality is a measure of the number of deaths in a population, scaled to that population, per unit time. Emigration is the movement of individuals or their dissemules out of a population area. Immigration is the one- way inward movement of individuals or their dissemules into a population or a population area.

4.

a) Fecundity refers to the fecundity, having the potential to produce very large numbers of offspring in their lifetimes b) Different species have different rate of fecundity. For example, female mosquitoes have one of the highest fecundity while hippopotamus female can only give birth to twenty off springs in her lifetime. c) Star fish can lay over 1 million eggs per year. In contrast, a female hippopotamus may have the potential to give birth to just 20 young in an entire lifetime of 45 years.

5. Type I, Type II and Type III are the three different patterns in “survivorship” that species exhibit. a) Type I

b) Type II

c) Type III

b and c) Type I pattern has very low mortality rates until they are beyond their reproductive years and have a correspondingly long life expectancy. Such species are typically slow to reach sexual maturity and produce relatively small numbers of offspring. Type II species are intermediate between these forms and tend to show a uniform risk of mortality throughout their life. Type III has a very high mortality rates when they are young while those individuals that do reach sexual maturity have a greatly reduced mortality rate. They often produce large numbers of offspring. The result is a very low average life expectancy for the species. The green sea turtle is an example of a species with many type III characteristics. 6) Under natural conditions, the number of offspring that are actually produced in an individual’s lifetime, their fertility is often significantly less than their fecundity. Food availability, mating success and disease are just a few of the many factors that act to limit reproductive potential.

7.

a) Population change formula:

b)

c) An open population refers to a population that is influenced by the factors of natality, mortality, and migration. d) A closed population refers to one in which only natality and mortality determine population growth, since immigration and emigration do not occur. Closed animal populations are rare. e) Most wild populations are open, since they have the ability to immigrate and emigrate between populations that exist in different locations. An example of a closed population is a land-based population that exist on secluded islands such as a Peary Caribou Herd in an Arctic Island. f) Biotic potential refers to the maximum rate a population can increase under ideal conditions.

Factors Affecting Population Change 1. a) A density dependent factor is any factor that has a greater impact on a population as the population density increases. A death rate that rises as population density rises is said to be density dependent, as is as birth rate that falls with rising density. b) Factors such as competition for food or nutrients, predation, accumulation of toxic wastes and diseases are density dependent factors. c) Charles Darwin recognized that the struggle for available resources within a growing population would inherently limit population size. The struggle for survival involves such factors as competition, predation, disease, and other biological effects. 2. a) Intraspecific competition occurs when of the same species compete for the same resources in an ecosystem while interspecific competition occurs when individuals of two separate species share a

limiting resource in the same area. It is the competition for resources between plants, animals or decomposers. b) Overcrowding, increase in food and habitat competition, and diseases can be easily spread are some of the problems as the density of a population increases. 3. a) Predation is the interaction between species in which one species, the predator eats the other, the prey. b) Predation is also an important cause of density – dependent mortality for some prey populations if a predator encounters and captures more food as the population density of the prey increases. c) The impact of a disease on a population can be density dependent if the transmission rate of the disease depends on a certain level of overcrowding in the population. d) Allee effect is in which individuals may have a more difficult time surviving or reproducing if the population size is too small. e) Pigeons that breed in colonies require large numbers at their breeding grounds to provide the necessary stimulation require in reproduction is an example of an Allee effect. f) The minimum viable population size is the smallest number of individuals needed to perpetuate a population. 4 a) A density independent factor is any factor that affects a population by the same percentage, regardless of density. b) An example of density independent factor is insecticide applications. c) Biomagnification is a result of insecticide application can lead to decreases in populations up the entire food chain, starting with the insects the chemicals are intended to harm. d) Top level carnivores are also susceptible to pesticide use because the animals that they eat such as insects can have been sprayed with pesticides which will enter the systems of these top level carnivores once they eat on animals that were contaminated with pesticides. e) The limiting factor determines how much the individual or population can grow. f) When a population sures the carrying capacity of its environment, the number of deaths starts to increase and the number of births starts to decline, resulting in a subsequent reduction in population size. Very high rates of mortality in a population may threaten a species with extinction. g) Population biologists monitor natural fluctuations in the size and density of populations. They do this, in part, to understand natural patterns better and, in part, to try to predict the organisms’ ability to withstand such impacts as natural disasters or destructive human activities.

Interaction within Communities 1.

a) The sum of total of a species’ use of the biotic and abiotic resources in its environment is called the ecological niche. b) A fundamental niche is studying an organism in the absence of predators or competition. It is used so that biologists are able to observe how the organism lives if it did not have to struggle for food or

worry about predation. A realized niche is the role an organism plays in the wild where all factors are taken into when studying the organism. Predation is what prevents these two niches from being identical. 2.

a) b) Symbiosis includes a variety of interactions in which two species live together in close, usually physical, association. Parasitism,mutualism, and commensalism are three general types of symbiotic interactions. c) The three types of symbiosis are parasitism, mutualism and commensalism.

3. a)

Interspecific competition occurs between individuals of different populations and, like intraspecific competition, it serves to restrict population growth. Interspecific competition can occur in two ways. Actual fighting over resources is called interference competition, while the consumption or use of shared resources is referred to as exploitative competition.

b) c) Russian ecologist G.F. Gause demonstrated that the more niches that overlap, the greater the competition between species. Gause’s experiments led to the conclusion that if resources are limited, no two species can remain in competition for exactly the same niche indefinitely. This became known as Gause’s principle, or the principle of competitive exclusion.

4. The three possible results of interspecific competition are : The population size of the weaker competitor could decline, one species could change its behaviour so that it is able to survive using different resources and individuals in one population could migrate to another habitat where resources are more plentiful. 5. Resource partitioning is the avoidance of, or reduction in, competition for similar resources by individuals of different species occupying different nonoverlapping ecological niche. An example is an Anolis lizard, to minimize competition for food, several species partition their tree habitats by occupying different perching sites. 6. Predation

1.

2.

The predator and prey relationship is always interchangeable in relation to one another. It is most of the time a cycle. It always starts with the population of the predator for as it increases the prey population declines. When the prey population increases, there is also abundance with the predator population. As the population of the predator increases, overpowering the population of the prey, the population of the prey would decline.

3.