Populations and Resources
Population
Is a group of organisms of one speciesthat lives in the same place, at thesame time, and can successfullyreproduce.
Example: Elephants.
Dynamic characteristics of populations
Size, number ofindividuals (N)
Density (N/ area)
Dispersion,
Random, uniform,clumped,
(appropriate scale)
Population Dispersion Patterns
Random
Uniform
Clumped
Dynamic characteristics of populations
Age distribution,
proportions of young, middle-aged, old
Differs in growing, stable, decreasing populations
Changes in populations
Growth
Decline
May affect size, density, dispersion, agedistribution.
May be affected by size, density, dispersion,age distribution.
Changes in populations
Growth
Expansion of species’ populations may lead toevolution of new species
Decline
Shrinking species’ populations may lead toextinction
Small populations
Narrowly specialized species
02 June 2010
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Populations.ppt
Changes in populations
ΔN = +B +I –D –E
+B = births (birth rate)
+I = immigrants (immigration rate)
– D = deaths (death rate)
– E = emigrants (emigration rate)
(For many [most] natural populations I and E areminimal.)
Exponential Growth
Accelerating growththat produces a J-likecurve when thepopulation isgraphed.
Only occurs for shortperiods in nature
Usually when theorganism has a lot ofresources.
Limiting Factors
Exponential growth cannot besustained in nature because noecosystem has an unlimited supply ofresources.
These restrictions are called limitingfactors.
Abiotic limiting factors: temperature,pH, oxygen, light, hiding places
Biotic limiting factors: food, etc.
Factors which can limit thegrowth of a population include:
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Carrying Capacity
Is the size of a population that can besupported indefinitely by the resources andservices of an ecosystem.
When a population is maintained at its carryingcapacity, it is at anequilibrium or balance.
There is an equalamount of organismsbeing born or movinginto the ecosystemas there are dyingor leaving.
Carrying Capacity
“The largest number of individuals in aspecies that an environment cansupport.”
4 factors that determine carrying capacity:
1.Materials/energy
2.Food Chains
3.Competition
4.Density
Materials and Energy
All populations are limited by theavailability of resources:
Energy (from the sun)
Water
Oxygen
Carbon
Nitrogen
Other nutrients
Food Chains
The Pyramids of Biomass, Energy, andNumbers demonstrate how the populationof a given organism is limited by:
its position in a food chain/web
the population size of those populations above andbelow it
Relationships:
Producer – consumer - decomposer
Predator - prey
Competition
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Density
An organisms’ need for space depends ontheir size, environment, and way of life.
Different species have different needs forspace.
This need for space determines how manyindividuals of a given species can live in thesame area at the same time.
Factors affecting population size may be:
1.Density-Dependent Factors
2.Density-Independent Factors
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If population density increases, it cancause a decrease in the population.
Overcrowding leads to:
Increased stress = spread of disease and parasites
Increased aggression = neglect of offspring
Reduced access to resources, mates and habitat
Increased death rate/decreased birth rate=decrease in population
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Events that can decrease population sizethat are not related to how manyindividuals are in the population tobegin with:
Forest fire
Flood
Volcano
Extreme weather (ex. Hurricane)
Pollution
Graphing Carrying Capacity
Humans and Carrying Capacity
Humans alter natural ecosystems often,causing a change to carrying capacities.
Urban sprawl is the growth of relatively low-density development on the edges of urbanareas.
Human population in the Golden Horseshoeis expected to increase by 3.7 millionbetween 2005 and 2031. How do we makeroom for all these people without affectingother ecosystems?
Easter Island
Discovered by Polynesians ~ A.D. 1000
Population grew to several thousand
Used trees for canoes to hunt dolphins
Used wood for cooking
Also ate birds, eggs, vegetables
Resources (trees) depleted
No canoes, no dolphins
Warfare over land, food resources
Population fell to ~ 100 when discovered byDutch, Easter Sunday 1722.
Ecological Niche
As species go about their dailyactivities, they interact with otherspecies.
An ecological niche is the way anorganism occupies a position in anecosystem, including abiotic and bioticfactors.
Example: brown bat
Biotic niche: insectsthat it eats, itscompetitors like thenighthawk, and itspredators.
Abiotic niche: placefor roosting andhibernation, the timeof night it hunts,airspace it flies in,the temperaturerange it can live at.
Population Regulation
Predators: organism that kills and consumesother organisms
Prey: is eaten as food by a predator
Bottom-Up Population regulation: a shortageof plant resource at the base of the foodchain causes declines in the animals in thehigher trophic levels.
Top-Down Population regulation: morerabbits in a population, lead to more coyotesto eat them, then more coyotes lead to fewerrabbits.
Competition
Competition occurs when 2 or moreorganisms compete for the sameresource.
Can limit size of population
Can influence the ecological niche ofan organism
Symbiosis
Mutualism: 2 species benefit from therelationship
Example: algae lives in coral. The algaegives the coral energy and the coral givesthe algae protection and carbon dioxide.
Commensalism: 1 species benefitswhile the other is unaffected.
Parasitism: when an organism benefitsat the expense of a different organism.