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Transcript of 1 Population Ecology Chapter 55 2 Environmental Challenge Ecology: the study of how organisms relate...
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Population EcologyChapter 55
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Environmental Challenge
• Ecology: the study of how organisms relate to one another and to their environments
• Abiotic: non-living; wind, temperature, water, sunlight, soil
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• Homeostasis: a steady-state internal environment regardless of external environment
• Beetle is catching water to help live in a dry environment
Environmental Challenge
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• Conformers: bodies adopting the temperature, salinity of their surroundings
Environmental Challenge
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• Morphological capabilities
– Adaptations that minimize energy expenditure
• Thick coats during the winter
• Wolf’s fur 3xs thicker in winter for insulation purposes
Environmental Challenge
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• Behavioral responses– Moving from one habitat to another– Maintain body temperature
• Going into the sun when cold• Going into the shade when hot
– Spadefoot toads• Burrow down in the sand to avoid the
heat
Environmental Challenge
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• Natural selection leads to evolutionary adaptation to environmental conditions– Allen’s rule of reduced surface area:
Mammals from colder climates have shorter ears and limbs
– Desert frogs: evolved a greatly reduced rate of water loss through their skin
Environmental Challenge
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Populations
• 3 characteristics of population ecology
– Population range: area
– Pattern of spacing
– changes in size through time
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Populations• Range
– Most species have limited geographic range• Devil’s hole pupfish lives in a single
spring in southern Nevada
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PopulationsIndividuals in populations exhibit different spacing
patterns–Random spacing:individuals do not interact strongly with one another; not common in nature
–Uniform spacing: behavioral interactions, resource competition
–Clumped spacing: uneven distribution of resources;
common in
nature
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Populations• Metapopulations: occur in areas in which suitable habitat is patchily
distributed
• Butterfly
Source-sink metapopulations: some areas are suitable for long-term habitat others are not– Continuous colonization of empty patches– Prevent long-term extinction
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Demography and Dynamics
• Demography: the quantitative study of populations
– How size changes
– Study birth and death rates of a specific age
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Demography and Dynamics
Generation times: time between birth of an individual and birth of its offspring
• Life span: correlated with generation time. Short generation time equals fast population growth rate, short life span
• Age structure: numbers of individuals in a different age group
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Demography and Dynamics
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Demography and Dynamics
Life tables show probability of survival and reproduction through a cohort’s life
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Demography and Dynamics• Survivorship: percent of an original
population that survives to a given age
• Survivorship curve: express some aspects of age distribution I. High death rate in
post-reproductive years
I. High death rate in post-reproductive years
II. Constant mortality rate throughout life span
II. Constant mortality rate throughout life span
III. Very high early mortality but the few survivors then live long (stay reproductive)
III. Very high early mortality but the few survivors then live long (stay reproductive)
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Life History• Life history: complete life cycle of
an organism• Trade-offs– Limited resources:• Decrease
survival• increased
reproduction• Reduction
of future reproduction
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Life History
• Individuals that delay reproduction may grow faster and larger, enhancing future reproduction
• Cost of reproduction: add or remove eggs
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Life History
Variation in baby side-blotched lizards
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Life History
• Age at first reproduction correlates with life span
– Long-lived species delay reproduction
• Advantage: juveniles gain experience before high cost of reproduction
– Short-lived species reproduce early
• Time is important, delay may mean no offspring
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Growth and Limits
• Biotic potential: growth when there are no limits on population growth: then:
dN=riN
dt
N = # of individualsr = rate of growthri = intrinsic ratet = timed = rate of change
every pair has 4 offspringevery pair has 4 offspring
every pair has 3 offspringevery pair has 3 offspring
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Growth and Limits• The biotic potential of any population is
exponential, even when the rate of increase remains constant
• The actual number of individuals accelerates rapidly
Time
Gro
wth
Rat
e
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Growth and Limits
• Carrying capacity: symbolized by K, is the maximum number of individuals that the environment can support
• Logistic growth model: applies to populations as they reach K
dN/dt = rN (K-N)/K
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Growth and Limits• If you plot N versus t, you obtain a sigmoidal
growth curve• As N approaches K, the rate of population
growth begins to slow• If N = K the population growth rate is zero• If the population size
exceeds K the population size will decline until it reaches K
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Growth and Limits
Many populations exhibit logistic growth
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Factors that Regulate
Density-dependent: factors that affect the population and depend on population
size
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Factors that Regulate
• Negative feedback:
– population size increases
• reproductive rates decline
• mortality rates increase
• or both
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Factors that Regulate
Positive feedback: Allee effect (Warder Allee). Growth rates increase with population size
At high populations, locusts have different hormonal and physical characteristics and take off as a swarm
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Factors that Regulate
• Density-independent effects: the rate of growth of a population unrelated to the size of the population
• External environment aspects: cold winters, droughts, storms, volcanic eruptions
• Populations display erratic growth patterns because of these events
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Factors that Regulate
• North American snowshoe hare has a 10 year cycle
• Population numbers fall 10-fold to 30-fold in a cycle and 100-fold changes can occur
• Two factors generate this cycle:
– Food plants
– Predators
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Factors that Regulate
Linked population cycles of the snowshoe hare and the Canada lynx
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Factors that Regulate
• Selection will favor individuals that can compete and utilize resources efficiently
• Can lower reproductive rates• K-selected populations: adapted to
thrive when population is near its carrying capacity
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Factors that Regulate
• Populations far below carrying capacity, resources abundant
• Costs of reproduction are low • r - selected populations: selection
favors individuals with the highest reproductive rates
• Most natural populations show life history adaptations that exist along a continuum of r and K - selected traits
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Factors that Regulate
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Human Population Growth
• K-selected life history traits– Small brood size– Late reproduction– High degree of parental care
• Human populations have grown exponentially– Last 300 years birth rate has
remained– Death rate has fallen dramatically
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History of human population size
Human Population Growth
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Population Pyramid: a bar graph displaying the number of people in each
age category
Human Population Growth
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Earth’s rapidly growing human population constitutes, perhaps, the
greatest challenge to the future of the biosphere
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• Uneven distribution among countries
• Increasing gap between rich and poor
• The world ecosystem is already under stress
• What is K for the human population?
• Thomas Malthus: Essay on the Principle of Population
Human Population Growth
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Human Population Growth
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• World population growth rate is declining:– High of 2.0% in 1965-1970– 2005: 1.2%– Still and increase of 78 million people
per year
Human Population Growth
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• Consumption in the developed world further depletes resources– Wealthiest 20% of the world’s
population accounts for 86% consumption of resources and produces 53% of CO2 emissions
– Poorest countries: 20% is responsible for 1.3% consumption and 3% CO2 emissions
Human Population Growth
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Ecological Footprint: amount of productive land required to support an individual at the standard of living of a particular population through the course of his/her life
Human Population Growth