What factors will increase or decrease the size of a population? SBI4U RHSA

 The patterns of population growth are governed by an intersection of many factors. Two common growth patterns for populations are:  1. Exponential Growth  This occurs when there are unlimited resources and no competition so the population skyrockets.

 2. Logistic Growth  This starts with exponential growth but the growth slows as population increases, resources become limited and finally the carrying capacity of an ecosystem is reached.  Carrying capacity (K) is the maximum population size that can be sustained in an environment for a long time.

 The two major categories of factors influencing population growth are:  1. Density Independent or Abiotic Factors  These factors cause a population to stop growing or crash long before the carrying capacity is reached. These factors usually produce sudden dramatic declines in a population.  Examples include: Heat waves, fires, floods, droughts, tornados, ice storms, mudslides

 2. Density Dependent or Biotic Factors  These factors slow a population’s growth as the population nears its carrying capacity. These BIOTIC factors often lead to sinusoidal growth patterns where the population size fluctuates around K.  Examples include: Immigration and emigration levels, waste accumulation, health/spread of diseases, competition for resources, behaviour like territoriality or predation

 This shows sinusoidal population growth as a the population increases over the carrying capacity more individuals die or fail to reproduce thus decreasing the population.

SPECIES ASPECIES B Positive (+)Neutral (0)Negative(-) Positive (+)MUTUALISM -cowbirds + cows Neutral (0)COMMENSALISM -barnacles on whales NEUTRALISM - probably non- existent Negative (-)PREDATION or PARASITISM - only the predator or the parasite benefit AMENSALISM - bread mould produces penicillin that kills bacteria COMPETITION - both species have decreased fitness

 Symbiosis includes mutualism, commensalism, predation and parasitism because in each interaction there is always one species that benefits.

 Two Types of Competition  1. Intraspecific Competition  - (within a species)  When the population size is large members of the same species compete with each other for food, breeding sites, shelter, water, sunlight, soil and nutrients.

 2.a) Interspecific Competition - (between different species)  When two different species share a similar habitat they can compete for resources. This indicates that the species have similar niches.

 This situation leads to the competitive exclusion principle which states that species with the same niche cannot co-exist; one will always exclude the other through evolution. This often leads to a change in the species.

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