Chapter 12 Flashcards
(40 cards)
Demography
the study of populations.
In the 19th century, Charles Darwin and other scientists realized that the study of demography could apply to all organisms on Earth.
Growth rate
in a population, the number of new individuals that are produced per unit of =me minus the number of individuals that die.
Intrinsic growth rate (r)
the highest possible per capita growth rate for a population.
Under ideal conditions, individuals experience maximum r (i.e., maximum reproductive rates and minimum death rates).
Exponential growth model
a model of population growth in which the population increases continuously at an exponential rate; can be described by the equation: Nt=N0e^rt
Nt = future population size; N0 = current population size r = intrinsic growth rate; t = time over which a population grows
J-shaped curve
the shape of exponential growth when graphed.
What is the main equation?
dN/dt=rN
Geometric growth model
a model of population growth that compares population sizes at regular time intervals.
The geometric growth model is expressed as a ratio of a popula=on’s size in one year to its size in the preceding year (λ).
When λ > 1, popula=on size has increased; when λ < 1, population size has decreased; λ cannot be negative.
According to the geometric growth model, the size of a population after one time interval is_______________;
After two time intervals, the population size would be___________
N1=N0λ: N2=N0λ^2
To determine the change in population size (ΔN) between initial population size and time intervals
(delta)N=N0λ^t-N0
When a population is decreasing
λ < 1 and r < 0
When a population is constant
λ = 1 and r = 0
When a population is increasing
λ > 1 and r > 0
Density independent
factors that limit population size regardless of the population’s density.
Common factors include climactic events (e.g., tornadoes, floods, extreme temperatures, and droughts).
Density dependent
factors that affect population size in relation to the population’s density.
Negative density dependence
when the rate of population growth decreases as population density increases.
The most common factors that cause negative density dependence are limiting resources (e.g., food, nesting sites, physical space).
Self-thinning curve
a graphical relationship that shows how decreases in population density over time lead to increases in the size of each individual in the population; often has a slope of -3/2.
Positive density dependence
when the rate of population growth increases as population density increases (also known as inverse density dependence, or Allee effect).
Positive density dependence typically occurs when population densities are low, which may make it hard to find mates, particularly when sex ratios are uneven.
Carrying capacity (K)
the maximum population size that can be supported by the environment.
Logistic growth model
a growth model that describes slowing growth of populations at high densities; it is represented by: (dN/dt)=rN(1-N/K)
S-shaped curve
the shape of the curve when a population is graphed over time using the logistic growth model.
Inflection point
the point on a sigmoidal growth curve at which the population has its highest growth rate.
Age structure pyramids with broad bases indicate
a growing population.
Pyramids with narrow bases indicate
a declining population.
Pyramids with straight sides indicate
a stable population.
