Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Factors that affect populations • What aspects of the ecosystem can limit the population of a species? • Anything that changes the relationship between births, deaths, immigrations and emigrations will change the overall population size. • A limiting factor = a factor that causes population growth to decrease • Some limiting factors include: – – – – – – Access to resources Competition Predation Parasitism and disease Drought and other climate extremes Human disturbances Limiting Factors • There are 2 main categories of limiting factors: – Density-dependent factors- factor that depends on the size of the population to act – Density-independent factors- affect all populations in similar ways, regardless of population size Density-Dependent Factors • A limiting factor that depends on population size including: – Intra and interspecific Competition – organisms struggle for resources – Predation – predator-prey relationship controls population of both the predator and the prey – Parasitism – control population by weakening/killing host. Less hosts= less parasites as well. – Disease - control population by weakening/killing host • Density dependent factors become limiting only when the population density (number of organisms per unit area) reaches a certain level • These factors operate most strongly when a population is large and dense Competition • As resources become more scarce competition for that resources increases • With greater competition, there is a larger struggle for survival • It becomes more likely that a given individual will not succeed. Intraspecific Competition Predator-Prey Relationship • The number of predators and prey in a system are directly related – – – – Predators increase- Prey decreases Prey decreases- predator decreases Predator decreases- prey increases Prey increases- predator increases Disease Density-Independent Factors • Affect all populations in similar ways, regardless of the population size including: – – – – Unusual weather Natural disasters Seasonal cycles Human activities (damming rivers/clearing forests) • Many species will show a characteristic “crash,” then the population will build back up right away, or stay low for some time • Environments are always changing, and most populations can adapt to a certain amount of change by growing or shrinking in size. • Major upsets in the ecosystem can lead to long-term declines in certain populations (human activities) Density Independent- Extreme Weather Seasonal Human Activities Overexploitation of cod fishery- grand banks