population dynamics
DESCRIPTION
Population Dynamics. April 28, 2004. Population (def.) – a group of actively interbreeding individuals Therefore, they’re the same species Individuals are in the same place at the same time Groups of the same species can be separated They become separate populations. Review. - PowerPoint PPT PresentationTRANSCRIPT
Review
Population (def.) – a group of actively interbreeding individuals Therefore, they’re the same species Individuals are in the same place at the same
time Groups of the same species can be separated
They become separate populations
Factors influencing growth rates of populations Population density Population size Population dispersion Age structure Sex ratio Environmental factors
Population Density
Def. – the number of individuals/area Eg. #prairie dogs/acre
Larger density means that population growth increases But as growth increases, certain factors begin to
limit growth = limiting factors Eventually, population growth decreases
Limiting Factors
Fewer resources Parasites and disease Predation Physiological and sociological changes
Population Size
The number of individuals in a population at a given time
Small populations Less genetically diverse Less resistant to disease
Large populations More genetically diverse More resistant to disease
Optimum size
Population Dispersion
The spatial pattern in which the individuals of a population are distributed
3 patterns Clumping Uniformly dispersed Randomly dispersed
Patterns vary in response to limiting factors
Age Structure
The proportion of individuals in each age group in a population
3 groups Prereproductive Reproductive Postreproductive
Each age group has a characteristic birth rate and death rate Birth rate = the number of offspring produced during a certain
amount of time Death rate = The number of individuals who die during a certain
amount of time
Generation Time
The average life span between the birth of individuals and the birth of their offspring
Related to body size A shorter generation time will result in
faster population growth
Sex Ratio
The proportion of individuals of each sex The number of females is usually directly
related to the number of births that can be expected
Environmental Factors Affecting Population Growth
Abiotic Biotic Ability to adapt to environmental change
Natural selection Evolution
Fig. 9.3, p. 200
POPULATION SIZE
Growth factors(biotic potential)
Favorable lightFavorable temperatureFavorable chemical environment(optimal level of critical nutrients)
Abiotic
BioticHigh reproductive rate
Generalized niche
Adequate food supply
Suitable habitat
Ability to compete for resources
Ability to hide from or defendagainst predatorsAbility to resist diseases and parasitesAbility to migrate and live in other habitatsAbility to adapt to environmentalchange
Decrease factors(environmental resistance)
Too much or too little lightTemperature too high or too lowUnfavorable chemical environment(too much or too little of critical nutrients)
Abiotic
BioticLow reproductive rate
Specialized niche
Inadequate food supply
Unsuitable or destroyed habitat
Too many competitorsInsufficient ability to hide from or defendagainst predatorsInability to resist diseases and parasitesInability to migrate and live in other habitatsInability to adapt to environmentalchange
Growth Factors
Growth Curves
Demography = the study of factors that affect the growth and decline of populations
Growth = (birth + immigration) – (death + emigration)
Populations grow exponentially Yields a J-curve
Plotted in terms of doubling time
Doubling Paper ThicknessDoubling Paper Thickness
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10000000
20000000
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70000000
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Number of Times Doubled
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Limitations Affecting Growth
Environmental Resistance Determines the carrying capacity (K)
S-curve – population fluctuates around K.
K-selected species
Boom and bust curve – species grow exponentially and use up their resources
R-selected species
Fig. 9.10b, p. 205
Fewer, larger offspringHigh parental care and protection of offspringLater reproductive ageMost offspring survive to reproductive ageLarger adultsAdapted to stable climate and environmental conditionsLower population growth rate (r)Population size fairly stable and usually close to carrying capacity (K)Specialist nicheHigh ability to competeLate successional species
elephant saguaro
K-Selected Species
Fig. 9.5, p. 201
2.0
1.5
1.0
.5
Nu
mb
er o
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eep
(m
illio
ns)
1800 1825 1850 1875 1900 1925Year
Sheep in Tasmania
Fig. 9.10a, p. 205
r-Selected Species
cockroach dandelion
Many small offspringLittle or no parental care and protection of offspringEarly reproductive ageMost offspring die before reaching reproductive ageSmall adultsAdapted to unstable climate and environmental conditionsHigh population growth rate (r)Population size fluctuates wildly above and below carrying capacity (K)Generalist nicheLow ability to competeEarly successional species