lecture 13
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Lecture 13: Population Growth
Covers Chapter 26
Some Definitions*
• Population: all of the members of a particular species that live within an ecosystem
• Community: a group of interacting populations• Ecosystem: all of the living and non-living components of
a defined geographic area• Biomes: Large land areas with similar environmental
conditions and characteristic plant communities• Biosphere: all living and non-living components covering
Earth’s surface• Ecology: the study of interrelationships of organisms with
each other and with their non-living environment
Population Change
• *Populations change through – Births– Deaths– Migration: net migration depends on
• Immigration (entering the population) • Emigration (leaving the population)
• The natural increase in population is difference between births and deaths.
• The total change in a population size is births minus deaths plus net migration.
births immigration
deaths
(births deaths) (immigrants emigrants) change in population size
emigration
Population Change
Fig. 26-1
2 opposing factors affect population change*
• Biotic Potential: maximum rate at which a population could increase assuming ideal conditions
• Carrying Capacity: maximum population size that can be sustained– for an extended period of time*
– without damage to the ecosystem*
Biotic Potential stimulates population growth
• Factors influencing biotic potential:– Age at which organism first reproduces*– Frequency of reproduction*– Average number of offspring produced each
time an organism reproduces*– Length of organism’s reproductive lifespan*– Death rate of individuals under ideal
conditions*
Carrying Capacity limits population growth
• If population exceeds carrying capacity, surrounding resources cannot feed all of the members of the population…then – the population will stop growing (and eventually begin
to shrink)
– the carrying capacity will shrink (because resources cannot renew themselves quickly enough)*
Fig. 26-6a
(a) An S-shaped growth curve stabilizes at carrying capacity
Growth stops and thepopulation stabilizes close to the carrying capacity
Populationgrows rapidly
Growthrate slows
Carrying Capacity Adjusts
Fig. 26-6b
(b) Consequences of exceeding carrying capacity
High damage; the carrying capacity ispermanently lowered
Low damage; resourcesrecover, and the population fluctuates
Extremedamage; thepopulationdies out
The populationovershoots thecarrying capacity; the environmentis damaged
Environmental Resistance*
• Degree to which the living and non-living environment limits population growth.
• A way to quantify environmental resistance is to divide factors that limit population growth into – density-dependent factors
– density-independent factors
Density dependent and density independent factors: overview*
• Density Dependent: factors that limit population size more when populations are larger– Competition– Predation– Parasitism– Availability of Nutrients– Availability of Space– Availability of Energy
• Density Independent: factors that limit population size regardless of how large/concentrated the population is– Climate and Weather– Human activities: pesticides, pollution
Density Dependent*• These factors become more effective at
limiting growth as the population grows/becomes more dense:– Competition: interactions among individuals
who attempt to use the same resources-harms both species involved
– Predation: organisms kill/eat other organisms– Parasitism: one organism (parasite) feeds off of
a larger one (host)-harms the host only
Fig. 26-11
bean weevils (prey)
A high predator population reduces the prey population
The prey populationpeaks when thepredator populationis low
braconid wasp (predator)
More next lecture
• Next lecture will be a more in depth look at competition, predation, etc…..community interactions.
• Today we are talking more about how these factors affect population growth.
Density Independent*
• Climate and weather
• Human activity– Some populations evolve adaptations to survive
climate/weather• thick coats for winter that are shed in
spring/summer
• Migration to warmer climate or one with more resources for a period of time
• Plants have dormant period during winter
Population Distribution*
• Populations show characteristic spacing, which may vary with time:
• Clumped: members live in groups (herds, packs, prides, flocks and schools)
– Many eyes to see food
– Protection from predators
– Some species clump near resources (trees near water)
• Uniform: members maintain a relatively constant distance between each other
– Territorial behavior: stay farther apart from others because of limited resources (plants, birds, etc)
• Random: rare
– Resources equally available
– Trees and other plants mostly
Populations Distribution
• Great pacific media (You Tube)
Clumped Distribution
Fig. 26-14a
Uniform Distribution
Fig. 26-14b
Random Distribution
Fig. 26-14c
What about the human population?
• Demography: study of the changing human population– Measure populations in different countries/regions– Track population changes– Make comparisons between developed and third world
countries– Examine birth/death rates among different sexes &
races– Attempt to estimate future population changes– Evaluate the impact of these changes
Humans• Human population growth used to be
exponential: continually accelerating increase. Now it seems we may be leveling off…..at least some think so.
• It took 200,000 years to get to 1 billion (1804), but now in 2012 we are at 7 billion– 1.4 million born each week– What about environmental resistance?– Are we at carrying capacity?
7 billion: Nat Geo Magazine
• You Tube
Humans and Environmental Resistance
• Humans have encountered resistance, but we have developed ways to overcome it:– Discovered fire*– Tools & weapons to kill food*– Shelter and clothing to live in cold areas*– Domesticated crops and animals for food*– Industrial and medical advances*– Scientific advances (discovery of bacteria)*
Population Growth is different in developed & developing countries
• Many factors determine population growth in different countries
Developed countries
• High standard of living• Access to modern technology• Access to medical care, including contraception• Education/employment opportunities• Decreased death rates, increased life span, more
stable birth rates• US is fastest growing developed country
Developing countries
• Higher birth rates (less access to contraception)
• More poverty
• Lack of education
Europe: 0.0%
Latin America/Caribbean: 1.5%
Asia (excluding China): 1.5%
Developing countries average: 1.5%
Africa: 2.4%
N. America: 0.6%
World average: 1.2%
Developedcountries average: 0.2%
China: 0.5%
Fig. 26-21
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