Organisms and Populations Test - 74

Allelopathy is a biological phenomenon by which an organism produces one or more biochemicals that influence the growth, survival, and reproduction of other organisms.  

Carrying capacity is the maximum population size of a species that an ecosystem can support indefinitely. When carrying capacity is reached, a population can survive on the resources available without depleting the overall availability of the resources. When a population is below the carrying capacity, the individuals have access to more than enough resources to survive. When a population grows and begins to reach the carrying capacity, the population begins using resources at an equal rate to which the resources are created. This often creates competition between individuals for the available resources. As a result, some individuals will die when they cannot get enough resources and others will not reproduce because they do not have the resources to support offspring. Environmental resistance leads to the establishment of a carrying capacity.

Commensalism is a relationship between two organisms where one receives a benefit or benefits from the other and the other is not affected by it. In other words, one is benefited and the other is neither benefited nor harmed.

A mutualistic relationship is when two organisms of different species work together and get benefit from the relationship. One example of a mutualistic relationship is that of the oxpecker (a kind of bird) and the rhinoceros or zebra. Flagellate protozoan living in the gut of termites is a case of mutualism where protozoa get nutrient (ingested wood) and termites get benefit from protozoa in cellulose digestion.

Exponential growth is the geometrical growth observed in a species when unlimited resources are available.

• Diapause is a period during which growth or development is suspended and physiological activity is diminished. Example in arthropods mainly in insects.
• Hibernation is an extended period of deep sleep. It is a state of inactivity and metabolic depression in endotherms. Example polar bears show hibernation.
• Phenotypic adaptation involves changes in the body of an organism in response to genetic mutation or certain environmental changes. For example, desert plants have thick cuticles and sunken stomata on the surface of their leaves to prevent transpiration.
• Commensalism is an association between two organisms in which one benefits and the other one neither benefits nor harm. For example, the interaction of an orchid growing on a mango tree where the orchid receives benefits from a mango tree and the mango tree is unaffected.

In an exponential population growth model, the change in population size may be determined by the following factors. Change in population size during a fixed time interval = birth during time interval-deaths during the time interval. Birth rate or natality rate is a measure of the extent to which a population replenishes itself through births. The death rate is the rate at which a population is losing individuals. D = mN, m = per capita death rate, N = population size, D = number of deaths per year.

A logistic growth rate primarily takes place when the growth rate decreases as the population reaches carrying capacity. It is characterized by a s-shaped graph. Letting N represent population size and t represent time, this model is formalized by the differential equation: dN/dt = rN/(1 - N/K) where the constant r defines the growth rate and K is the carrying capacity.

• In a symbiotic relationship, the two species in the relationship live together. Many organisms are involved in symbiotic relationships because this interaction provides benefits to both species. 
• Symbiotic relationships can be obligate or facultative. 
• Obligate symbiosis is when two organisms are in a symbiotic relationship because they can't survive without each other. 
• Facultative symbiosis is when the species live together by choice. There are four main types of symbiotic relationships: mutualism, commensalism, parasitism, and competition.

Mutualism is an interaction in which both individuals are benefited e.g., hermit crab gains protection from predators by its relationship with the sea anemone and in return provide food to the sea anemone. In a commensal relationship, one organism benefits while the other is unaffected. example e.g., sucker fish by attaching themselves to shark traveled to different places whereas shark remains unaffected. Parasitism is an interaction in which one is benefited at the expense of the other organism e.g., Cuscuta is a parasitic plant which is parasitic on the roots of Cissus. Predation is a biological interaction where a predator feeds on its prey e.g., tiger and deer wherein tiger which is a predator feed on deer which is a prey. Therefore, the correct answer is option B.