Download Chapter 55 Population Ecology

Population Ecology
Chapter 55
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Outline
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Population Ecology
Population Dispersion
Metapopulations
Demography
Cost of Reproduction
Biotic Potential
Influence of Population Density
Population Growth and Life History Models
Exponential Growth
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Ecology
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The distribution & abundance of an organism
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& its interactions with other organisms
(biotic)
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& its interactions with its environment
(abiotic)
Behavior
Genetics
Physiology
Ecology
Evolution
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Is ecology & environment the same?
Environment: immediate surroundings of an organism
macro-environment
micro-environment
Abiotic factors
temperature
salinity
H2O-dehydration/hydration
humidity
sunlight
photoperiod
O2/CO2
atmospheric pressure
pH
wind
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Environmental Variation
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Key elements of an organism’s environment
include:
– temperature
– water
– sunlight
– soil
Many organisms actively employ
mechanisms to maintain homeostasis, while
others conform to their environment.
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Responses to Environmental Change
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Individual responses
– physiology
– morphology
– behavior
Evolutionary responses
– Shorter ears and limbs (Allen’s Rule)
– Larger ears (Bergmann’s Rule)
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Morphological and Behavioral Adaptation
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Populations
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A population consists of group of interbreeding
individuals of a given species living together at the
same place at the same time
Population distributions
– Most species: limited geographic range
– Population ranges change through time.
§ environment changes
§ organisms circumvent previously inhospitable
habitat
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Altitudinal Shifts
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Population Dispersion
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Randomly spaced
– Individuals are randomly spaced within a
population.
Uniformly spaced
– Uniform spacing within a population often
results from resource competition.
Clumped spacing
– Individuals clump into groups or clusters in
response to uneven distribution of
resources in their immediate environment.
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Population Dispersion
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Population Dispersion
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Population Dispersion
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Human effect
– By altering the environment, humans have
allowed some species to expand their
ranges, although the overall effect has
most often been detrimental.
Dispersal mechanisms
– light seeds (wind)
– hooks and hairs (animal fur)
– fruits (animal digestive systems)
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Seed Adaptations
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Metapopulations
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Metapopulations are a network of distinct
populations interacting with each other by
exchanging individuals (genes).
– degree of interaction depends on dispersal
– Rate of extinction in habitats is balanced by
the rate of colonization of empty habitats.
– prevent long-term extinction
Source-sink metapopulations occur in areas
where some habitats are suitable for long-term
maintenance, while others are not.
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Demography
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Demography - statistical study of populations
Factors affecting growth rates
– sex ratio
§ effect also determined by mating habits
– generation time
§ average interval between birth of an
individual and the birth of its offspring
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Demography
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Age structure
– cohort - individuals of the same age
§ fecundity - number of offspring
produced in a given period of time
§ mortality - number of deaths in a given
period of time
– Age structure determined by the relative
number of individuals in each cohort.
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Demography
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Life tables
– constructed by following the fate of a cohort
from birth until death
Survivorship curves
– Survivorship is the percentage of an original
population that survives to a given age.
§ Type I - full life span
§ Type II - mortality unrelated to age
§ Type III - early susceptibility
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Survivorship Curves
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Cost of Reproduction
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A life history is the complete life cycle of an
organism.
– all involve significant trade-offs
§ Due to limited resources, increased
reproduction may decrease survival and
chances of future production.
v cost of reproduction
Ø Natural selection will favor the life
history that maximizes lifetime
reproductive success.
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Cost of Reproduction
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Investment per offspring
– Key reproductive tradeoff concerns the
amount of resources to invest in producing
any single offspring.
§ number of offspring versus size of each
offspring
v In many species, offspring size
critically affects chances of survival.
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Cost of Reproduction
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Reproductive events per lifetime
– semelparity - organisms focus all
reproductive efforts on a single, large event
– iteroparity - organisms produce offspring
several times over many seasons
Age at first reproduction
– Longer-lived animals tend to reproduce
later, and provide more parental care than
shorter-lived animals.
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Biotic Potential
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Exponential growth model
– Rate at which a population of a given
species will increase when no limits are
placed on the rate of growth.
§ Innate capacity for growth of any
population is exponential.
v Even when rate remains constant,
actual increase in number accelerates
as the population size grows.
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Biotic Potential
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Carrying capacity
– Carrying capacity (K) is the maximum
number of individuals the resources in a
given area can support.
Logistic growth
– As a population approaches carrying
capacity, its growth rate slows as resources
become depleted.
§ sigmoidal growth curve
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Population Growth
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Influence of Population Density
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Density-dependent population controls
– As populations approach their carrying
capacity, competition for resources can be
severe, leading to decreased birth rate
and increased risk of mortality.
§ In some cases, growth rates increase
with population size.
v Allee effect
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Influence of Population Density
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Density-independent population controls
– Growth of a population at any instant is
limited by some factor other than
population size.
§ external environmental conditions
Population cycles
– snowshoe hares
§ Food plants (willows) and predators
(lynx) both control the population.
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Linked Population Cycles
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Population Growth and Life History Models
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K-selected species tend to produce relatively
few, large offspring.
– large investment in parental care
r-selected species tend to produce many,
small offspring.
– small investment in parental care
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Exponential Growth
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Throughout most of human history, human
populations have been regulated by food
availability, disease, and predators.
– resemble K-selected species
– Due to the easing of environmental
restraints, the human population has
grown explosively over the last 300 years.
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Advent of Exponential Growth
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Population pyramids
– bar graph displaying number of people in
each age category
§ stable - rectangular
§ rapid growth - triangular
§ decreasing - inverted pyramid
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Population Pyramids
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Population Pyramids
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Uncertain future
– Earth’s rapidly growing human population
is possibly the greatest challenge facing
facing the biosphere.
– uneven resource distribution
§ population distribution
§ wealth gap
§ ecological footprint
Population growth rate on the decline
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Ecological Footprints
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Summary
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Population Ecology
Population Dispersion
Metapopulations
Demography
Cost of Reproduction
Biotic Potential
Influence of Population Density
Population Growth and Life History Models
Exponential Growth
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