Ecology of Populations
Popul ation Ecology = the study of how pop ulations interact with their environment
Popula tion = group of i ndividua ls of the same speci es occupy ing a common geographi cal area
Habi tat -where a sp ecies normal ly lives
Characteristics of populations - Each population has certain characteristics:
Popula tion size = number of i ndivi duals making up its gene po ol
Popul ation density = number of i ndivid uals per unit of area or vol ume, e.g. pers ons/squa re mil e
Population distribution = the general pattern in which the population members are dispersed through
its habi tat, may be: Cl umped (most common), Uni formly dispers ed (rare), or Randomly di spersed
Age s tructure defines the relati ve proporti ons of indivi duals of each age: Pre-reproductive,
Reproducti ve, and Pos t-reproductive
Population size and growth Population size is dependent on births, immigration, deaths, and
emig ra ti o n
Growth of Populations
Exponential growth: If birth and death rates of a population remain constant, they can be combined into one
variable r = net reproduction per individual per unit time (rate of increase)
Population growth may be represented mathematically as: G = rN Where G = population growth per unit time, r =
rate of increase and N= the number of individuals. When plotted against time a graph in the shape of a J will be
obtained denoting exponential growth, i.e. , one variable increases much faster than the other
As long as per capita birth rates remain even slightly above per ca pita death rates, a population will grow
exponentially - with ever-increasing rates a nd shorted "doubling t imes"
It took 2 million years for the world's human population to reach 1 billion, yet it took only 12 years to reach the
fifth bill ion
If a population lives under ideal conditions, it may display its biotic potential - the maximum rat e of increase under
ideal conditions. Few populations live under ideal conditions because a number of factors limit their growth
Limiting factor - any resource that is in short supply, e. g., food, minerals, light, living space, refuge from predators,
etc.
Carrying capacity = maximum number of individuals of a species or population a given environment can sustain.
Each habitat or area can only support so many individuals
Because of limiting factors populations rarely exhibit J shaped growth curves Logistic growth
Early on populations will exhibit very rapid growth but as they near the carrying capacity they will level off is called
logistic growth and itproduces an S shaped curve
Logistic growth is density dependent, i.e. the growth is affected by the density of individuals.
Intraspecific - competition among individuals
of the same species, e.g., humans compete
against other humans
Interspecific - competition between different
species, e.g., humans compete ag ainst a wide
variety of species seeking to utilize our food
resources
dN/dt = Nr
d= derivative
N= population size
T= Time
dN/dt = Nr (( K−N)/K )
d= derivative
N= pop.
r= intrinsic rate of natural increase
K carr ying capacit y
3 Assumptions
K is constant
Pop. growth i sn't affected by age
distri bution
Birth ra tes and sur vivors hip rates
increase and decrease linearly with
pop. size
Forest s
Trees dominate biome –ma jor producer
One-third of Earth’s land area – as forests
Global climate-buffering ca pacity in forests
Most diverse biotic communities in the world
Over two-thirds of the leaf area of land plants
–photosynthesis
About 70% of carbon present in living things –
carbon cycle
Canopy -affects other producers, consumers,
decomposers a nd their niches
Insects, birds, and mammals –key components
of food web
Potential medicines a nd many thousands of
unseen and undiscovered species
Human civilizations –bringing deforestation,
pollution, land use change, and industrial
usage problems
Forest types –depend upon climate (latitude)
and seasonal rainfall ▪Tropical ▪Temperate or
Deciduous ▪Boreal (taiga) or coniferous
Taiga/Boreal Forests
2nd largest forest type in the world
Lies between Arctic and Deciduous Forest –50
to 60 degrees North Latitude
Upper elevations of mountains
Angle of incidence for incoming solar radiation
is low and twilight lasts many hours
Seasons are divided into short, moist and
moderately warm summers a nd long, cold, dry
winters.
Temperature –vary greatly from summer to
winter (-65 to +70 degrees Fahrenheit)
Variable precipitation: 6-40 in (15-100 cm)
Soils –thin because they were scraped by
glaciers and very acidic because of
decomposition of pine needles
Absence of earth-churning invertebrates as
earthworms so soil is hard and compact
Fire a major factor in maintaining biome
Grassland s/Praries
Precipitation is too low to support
trees but too great for deserts to
form
Grasses are major producer with
several genera and species common
but usually with one or t wo
dominati ng
Most grasses possess rhizomes and
are wind pollinated
Moderate temperature with
notable extremes: -20°F t o 110°F
common, and even colder
temperatures in the north
Variable precipitation: 6-40 in (15-
100 cm)
Scattered rain and lightning
common in summer months
("convection storms") with more
general rains and snows in winter
months
Soils generally fertile, deep and rich;
varia ble
Growing season of 120-200 days
Generally flat to rolling topography
cut by stream drainages where
there is a river-bank ha bitat.
Fire a major factor in maintaining
biome
Dominated by grazing animals (deer,
antelope, buffalo -onc e common
but now rarely native to the range),
burrowing small animals, and
songbir ds.
Niche-Role an organism plays in a community
Fundamental-all the envi ronmental
conditions where the species is abl e to live in
Realized –the par t of the fndamental
niche wher e the s pecies actually lives in
Batesian Mimicry=a
harmless species has
evol ved to imi tate the
warni ng si gnals of a
harmful speci es to avoid
predators
Mullerian Mimicry= 2
harmful speci es evolve
the si mil ar warn ing
signals to a mutual
benefit
Clean Air Act (CAA) of 1970:
established national primary and
secondary air quality stand ards. Set
emission standard s for cars, and limits for
release of air pollutan ts.
