Ecology of a Population By:Tara Hill
Ecology of a Population
By:Tara Hill
Population Defined
A population is:
A group of organisms of the same species
occupying a particular space at a particular
time
Population Characteristics:
Distribution:where organisms are found on earth, determined by biotic/abiotic factors
Dispersion: spatial distribution of individuals of a population -- three general kinds of patterns:
clumped (aggregated) dispersion -- individuals clumped together -- resources in a habitat may be patchy in distribution which causes organisms to form "clumps"
Uniform-individuals are about equal distance from one another
-caused by competition among individuals in the same population
Random-habitat is relatively uniform so individuals are neither repelled or attracted to one another.
Population Size
A balance between:
• Natality=birth rate (b)
• Mortality=death rate (d)
(b)>(d)=population size increases
(b)<(d)=population size decrease
(b)=(d)=population size is constant
Factors affecting population size besides natality/mortality
• Immigration rate (i) (increases pop. size)
• Emigration rate (e) (decreases pop. size)
Growth rate equation:
r=(b-d) + (i-e)
Population Growth
Biotic Potential=
-promotes positive growth
-intrinsic factors(litter size, gestation)
Environmental Resistance=
-limits growth
-extrinsic factor(weather, food supply)
Patterns of growthExponential growth (J shaped curve)
• biotic potential(rm)=maximum value
Logistic growth (S shaped)
K=carrying capacity=population size that is based on number of resources available
Limiting factors:
Density dependent:
-competition
-disease
-predation
-food
Density independent:
-weather
-catastrophes
-natural disasters (typhoons, volcanoes)
Natural Selection:
• limiting factors place stresses on a population
• the best adapted organisms will survive and get to reproduce and pass on their genes with the adaptation to their offspring
• over long periods of time this can lead to a change in species
Population Growth
Biotic Potential=
-promotes positive growth
-intrinsic factors(litter size, gestation)
Environmental Resistance=
-limits growth
-extrinsic factor(weather, food supply)
Patterns of growthExponential growth (J shaped curve)
• biotic potential(rm)=maximum value
Logistic growth (S shaped)
K=carrying capacity=population size that is based on number of resources available
Limiting factors:
Density dependent:
-competition
-disease
-predation
-food
Density independent:
-weather
-catastrophes
-natural disasters (typhoons, volcanoes)
Natural Selection:
• limiting factors place stresses on a population
• the best adapted organisms will survive and get to reproduce and pass on their genes with the adaptation to their offspring
• over long periods of time this can lead to a change in species
• proportionally massive eyes
making vision acute for locating
prey
• movable ears for better hearing
making them good nocturnal
hunters
• can rotate their heads a full 180
degrees to help them avoid
predators such as wild cats
• Long back legs to help them
jump twenty feet, an important
survival skill in the jungle
• Long tail providing power for
jumping and holding onto tree
branches for stability
Ex:Phillipine Tarsier
Survivorship curves:
-based on a cohort of individuals from birth until death
-cohort=a group of individuals of the same age
-survivorship curves are meant to show the number of individuals surviving at each age for a particular species
-three types of curves
Type 1=good early survival, die of old age, low birth rates, provide lots of parental care (humans)
Type 2=die at constant rate regardless of age (birds, lizards)
Type3 =poor early survival,survival thatimproves with
age, lots of offspring, low parental care(fish,plants)
Life History Patterns:
r selected species: species inhabiting fluctuating or unpredictable environments-environments keep populations below carrying capacity (lots of predation, competition over resources)
k selected species-species inhabiting stable, predictable environments-keep population size near carrying capacity and resources are scarce