Biological Science: Bio 142 Chapter 54 Flashcards

Learning objectives

� Define geographic range and describe i) factors that influence a
species� range, and ii) factors that influence the distribution of
individuals within a species� range
� Define life history traits and explain why these traits are the
major components of individual fitness.
� Predict how ecological conditions will favor particular life
history strategies.
� Explain how life history traits influence population dynamics and age-structure.
� Explain why trade-offs occur among life history traits.

Biotic facors

The past and current presence of other species that provide habitat,
food, or competition

Abiotic factors

Temperature, rainfall, the presence of geographical structures like
mountains and oceans, and largescale ongoing and historical processes
such as continental drift


Geographic distribution and is dynamic as abiotic and biotic factors
change over time.

Arrangment patterns

Random, if the position of each individual is independent of
the others, as may occur when seeds are dispersed by the wind.
Clumped, if the quality of the habitat is patchy or the
organisms associate in social groups (such as schools of fish);
or Uniform, if negative interactions occur among individuals,
such as competition for space, water, or other resources.


The study of factors that determine the size and structure of
populations through time.

Factors that limit the geographic range of species


Distribution of populations within the range


Life history traits


Darwanian demon


Limited energy and competing demands produce trade offs among traits

Optimal life history strategy

Varies with ecological characteristics such as abiotic conditions,
resource availability, community composition and how these (and any
other factors) influence age-specific probability of survival

Optimal Life History Strategies Given a Trade-off Between Fecundity
and Survival


Life-history continuum

Learning objectives

� Describe the contents and assumptions of a life table and the
questions it can answer.
� Estimate age-specific survival and mortality rates from
population census or cohort data.
� Estimate age-specific reproductive output from life table data
and describe what information is needed to estimate that number.
� Calculate net reproductive rate of a population and explain how
life tables indicate whether a population is growing.
� Explain how life history traits influence population dynamics and age-structure.

Life Tables

Summarize age-specific survival and reproduction for a given population
Life tables tell us:
- At what age do individuals face the lowest/highest mortality risk?
- At what age are individuals investing most in reproduction?
- Population growth rate
- Estimated future population size
- Individuals of the same age are alike
- All female population

Two types of life tables


Cohort life table

Tag a cohort of individuals and decide on age interval to gather data
1) Tagged 115 newborn chicks leg bands
2) Censused population yearly for tagged individuals - survivors

Life table construction

- x = age
- nx = number alive at beginning of age x
- lx = Proportion of the original cohort surviving to age
"x" (year)
- lx = nx /n0
- dx = Number dying in the interval from year
"x" to "x + 1"
- dx = nx - nx+1
- qx = Mortality rate of each age
- qx: = dx / nx
- bx = # offspring per individual of age x
- lxbx = average number of female offspring
per year per original female

Net reproductive rate

Using the life table to estimate population growth

If R0 > 1, then the population will grow exponentially, if R0 <
1, the population will shrink exponentially, and if R0 = 1, the
population size will not change over time.
R0 ? r, r measures population change in absolute units of
time (e.g., years); R0 measures population change in terms of
generation time.

Learning objectives

� Estimate population growth under density-independent conditions
� Explain why and how populations change in size over time
� Contrast patterns of growth under density-independent vs.
density-dependent conditions
� Calculate rate of population growth at different population sizes


- the �per capita� or �instantaneous� growth rate and represents
population growth at any given time; dictates the shape of the
relationship between time and population size
- r is related to net reproductive rate in an exponential way and
population growth is inherently exponential

Exponential growth

- Population increases according to the equation:
Nt = N0ert
Nt = number of individuals after t units of time
N0 = initial population size at t = 0
e = the base of the natural logarithms
r = exponential growth rate
- When r is constant, population growth is EXPONENTIAL and density independent

Density Independent population growth

Conditions: Effectively unlimited resources/release of predation
Characteristics: Acceleration of population growth with increase in
population size
Population growth rate is close to maximum possible = rmax
Example: Colonization of new habitat, recolonization following disturbance

Density dependent population growth

Population growth rates change over time as density increases

Logistic growth

Begins exponentially and slows with increasing density
r = realized rate of growth rmax = intrinsic
growth rate (max possible; as in early growth) K = carrying
capacity of the environmentt The number of individuals of
the same species the environment can support
N = population size Two different solutions for the two
different N values

Population size changes as a result of density-independent and
density-dependent factors

Density-independent factors are usually abiotic change
birth rates and death rates irrespective of population size
Density-dependent factors are usually biotic
change birth rates and death rates as a function of
population size cause logistic population growth

Natural populations

Most natural populations fluctuate in size
Environmental changes (e.g., temperature, pH, catastrophes)
Direct effects (performance of individuals)
Indirect effects (e.g., changes in food supply)
Intrinsic responses Behavioral and life
history responses to changes in density