Presentation on theme: "Biology 213 Chapter 53 Introduction to Ecology: Population Ecology Part 1."— Presentation transcript:
Biology 213 Chapter 53 Introduction to Ecology: Population Ecology Part 1
You will be able to… List various fields of study in Ecology Explain what factors change populations Calculate population rate changes Compare and contrast density- dependent to density-independent factors
Ecology: Oikos = homeOlogy = study of Integrates all biological fields 1.Organismal ecology: physiology, behavior, interactions with environment 2.Population ecology: factors affecting groups of individuals in an area. 3.Community ecology: interactions between species in an area
4.Ecosystem ecology: biotic and abiotic interactions; E flow & chem. Cycles 5.Landscape ecology: exchange of E & materials across multiple ecosystems 6.Global ecology: biosphere: regional exchange of E & materials affecting entire functioning & distribution of organisms wotldwide.
Ecology & evolution: changes in environment impacting populations’ alleles over time. Ecology & environmental issues Complexity of Nature: Why are some species present in an area? Dispersal difficulties (accessibility?) Behaviour limits distribution (habitat preference)? Biotic factors: competition/parasitism/predation/etc Abiotic factors: Chem: H 2 O, O 2, pH, salinity, nutrients Phys: Macro & micro climate: Temp, light, fire, soil composition, moisture
Estimate: one million years to get from 2.5 million to human population of ~ 5 million people in 6000 B.C. (2x) population did not reach 500 million until almost 8,000 years later -about 1650 A.D (100x) doubled roughly once every thousand years or so reached a billion ~ 1850, doubling in 200 years reached two billion around 1930 – doubling in 80 years 1970’s it reached 4 billion ~ 40 year doubling time Today’s population ~ 7 billion
What factors have allowed human population to increase so rapidly?
Population size Population density Patterns of dispersion Demographics Population growth Limits on population growth Ecologists study population trends rather than individual organisms. Properties of populations include
Population density –# individuals of a species per unit at a given time Population dispersion (spacing) –How are individuals distributed in a habitat? –Why would this be important to know if you were studying a population? –What does a dispersion pattern tell you?
Individual members distributed in a # of different ways: Clumped - Uniform - Random -
Why would a clumped population pattern form? individuals _____________ to each other, or __________________________________.
What factors encourage a uniform population pattern? individual organisms actively _____ each other or all _________________________________
What abiotic or biotic features would encourage a random population pattern? Rare in nature - occurs in absence of strong attractions or repulsions among individuals.
Dispersion patterns and density may change over time Habitat changes: food, nutrients, water, sunlight (plants) Age / size / developmental stages change:
Four factors that produce changes in population size
Natality: birth rate
Mortality rate of cheetahs Increased Infant Mortality Is the cheetah dangerously inbred? Majority of deaths in wild due to predation. Future for cheetah population?
How a population changes: in # of individuals in a certain period of time N = r =
How a population changes: in # individuals / time N = # individuals r = * Per 1,000 individuals Growth rate =
Example: N = 300,000 humans: 3,000 births + 1,500 deaths in one year r= (birth rate) – (death rate)
Example: N = 300,000 humans: r= (birth rate) – (death rate) r=r= r =
Example: N = 300,000 humans: r = 0.005 x 100 = 0.5% increase rN = 0.5 x 300,000 rN =
If r is positive, increase in pop. If r is negative, pop. is decreasing If r = 0, population is stable
Are there other factors besides birth and death and size of a population that can change a population?
Immigration What causes immigration biologically? –Favorable factors
Factors encouraging immigration: New environment made available –Natural disasters large and small –Competitive or predatory species goes extinct / moves away –Climate change or new resources –Hitch-hiking (“alien” species) Less competition in new area
Succession after a disaster Immigrants have an opportunity to invade: Reduced competition
Factors that encourage successful immigration: Distribution methods: dispersal is at or near ground level vs. aerial dispersal dispersers actively engage in searching, or not dispersers able to orient toward preferred habitat from some distance, or not
Wind dispersing Golden Orb spiders
Emigration Unfavorable Factors: *Excessive competition: mates or food *Lack of resources *Disease *Avoidance of in-breeding
Population change includes immigration and emigration: r = (birth rate) – (death rate) plus (immigration – emigration) e.g. Example: N = 300,000 humans: 3000 births + 1500 deaths in one year 3,000 immigrated into the area 9,000 emigrated out of the area
r= (b – d) + (i – e) b – d = (10/1000) – (5/1000) = 0.005 i – e = 1/1000 – 3/1000 = 0.001 – 0.003 = -0.002 r = (b – d) + (i – e) = (0.005) + (-0.002) = 0.003 x 100 = 0.3% Growth rate: rN = (0.3%)(300,000) = 900 more people in the population
Intrinsic rate of increase (r max ) Maximum rate at which species or population can increase under ideal conditions Exponential population growth
Exponential population growth
According to Malthus: Population, when unchecked, increases in a geometrical ratio. Subsistence increases arithmetically.
Carrying capacity –Carrying capacity (K) = largest population maintained without degrading environment they live in –Changes as environment changes Logistic population curve (S-shaped curve)
Carrying capacity and logistic population growth Limiting Factors
Density-dependent factors –Regulate population growth by affecting large proportion of population as population rises:
Density-dependent factors –What do you think would impact a population as it got bigger? Predation Disease Competition Toxic wastes
Density-dependent factors and negative feedback
Density-independent factors –L–Limit population growth but are not influenced by changes in population density: usually ABIOTIC –E–Examples include natural disasters: Hurricanes Blizzards Forest fires Mudslides Volcanoes, tsunamis, and earthquakes
Limiting Factors Biotic and abiotic, Density dependent or independent factors that limit a population’s growth: What would be a limiting factor?
What can you think of that would be a limiting factor? Which are biotic and which are abiotic? increase death rate decrease birth rate limits immigration encourages emigration Any factors that slows population growth.
How are up & down cycles explained? Can be very complex relationships and factors.
Biology 213 Chapter 53 Introduction to Ecology: Population Ecology Part 2
You will be able to… Explain what factors change populations Calculate population rate changes Compare and contrast density-dependent to density-independent factors Analyze human population patterns and make predictions about future trends
Semelparous reproduction –Expend their energy in a Iteroparous reproduction –Exhibit ________________________ throughout their lifetimes
Semelparity: Expend energy to reproduce in one big effort Most insects, invertebrates, many annual plants, and some fish What’s the advantage?
Iteroparous reproduction Expend energy to reproduce in cycles Most vertebrates, perennial plants. What’s the advantage?
Species exhibiting an r strategy –Emphasizes a high growth rate –Organisms typically have small body size high reproductive rates short life spans inhabit variable environments Often
Species exhibiting a K strategy –M–Maintains a population near carrying capacity (K) of environment –S–Species often have large body size low reproductive rates long life spans inhabit stable environments Often
Survivorship curves –Type I Mortality is greatest in old age –Type II Mortality is spread evenly across all ages –Type III Mortality is greatest among the young
Survivorship curve for a herring gull population
Source habitats: –Preferred habitats –Local reproductive success is > local mortality –Local individuals disperse from source habitats to other regions
Sink habitats –Lower-quality habitats –Individuals may suffer death or poor reproductive success –What would make an organism move then?
Source & sink populations in a hypothetical metapopulation
Human population growth –World population reaches 6,668,926,425 by May 20, 2008 –Per capita growth rate declined from peak in 1965 of about 2% per year (doubling time 35 years) –to 1.3% per year (doubling time of 54 years) –birthrate necessary for zero population growth is 2.1 births per woman 7,000,000,000 The year 2011
Human population growth: exponential J-shaped curve so far
logistic population growth
Chapter 53 Clicker Question #4: Often growth cycles of one population affects the cycle of another. As moose populations increase, wolf populations also increase. If we consider the logistic equation for the wolf population: dN = rN (K-N) dt K which of the above factors accounts for the strongest impact on the moose population? A. KB. dNC. rND. dt
Population characteristics –H–Highly developed countries low birth rate low infant mortality low fertility rate long life expectancies high GNI PPP: –G–GNI PPP per capita is the gross national income in purchasing power parity divided by mid-year population.
Population characteristics –Developing countries high birth rate high infant mortality high fertility rate short life expectancies low GNI PPP
China and India’s populations increasing What trends do we see world-wide?
Birth rate decline lags behind as death rate decreases: e.g. in Mexico, 1900–2000
Age structure influences population dynamics –Possible for country to have replacement-level fertility and still experience population growth –Young age structure causes a positive population growth momentum as large pre-reproductive age group matures
Age structure diagrams comparing Kenya to USA to Germany 15-to-40 range: reproductive rates are high
“Carrying-capacity" definition of overpopulation: not population density, but #’s of people in an area relative to resources capacity to sustain human activities a condition of overpopulation might be corrected with no change in the number of people!
Developing countries tend to have people overpopulation that degrades the environment Developed countries have consumption overpopulation that degrades the environment Ecological Footprint
USA & Mexico One week’s food supply. One week’s food costs the American family $341.98
One week’s food Egypt Ecuador
Above: BhutanBelow: Chad One week’s food costs the Chad family $1.23
China has 22 % of world’s population India has 17 % of world’s population Both nations are modernizing rapidly USA uses has 4.4% of the world population and uses 25% of world’s energy resources What happens to global resources when developing countries want to enjoy a developed nation lifestyle like ours?