Download Understanding Populations

Understanding
Populations
Environmental Science
Holt Chapter 8
How Populations Change
in Size
Chapter 8.1
What is a population?
 Population: all the members of a species living in the same
place at the same time
 Refers to both the group in general and to the size of the group
Properties of Populations
 Populations may be described in terms of size, density or
dispersion.
 Population density is the number of individuals per unit area or
volume
 A population’s dispersion is the relative distribution or
arrangement of its individuals within a given amount of space
 May be even, clumped or random
How does a population grow?
 A population gains individuals with each new offspring or
birth and loses them with each death
 Growth rate: a change in the size of a population over a given
period of time
Change in population size = Births – Deaths
Can the growth rate be negative?
How fast can a population grow?
 A species’ biotic potential is the fastest rate at which its
populations can grow.
 Is limited by it’s reproductive potential
 Reproductive potential: the maximum number of offspring
that each member of the population can produce
How fast can a population grow?
 Populations may undergo exponential growth which means
they’ll grow faster and faster
 Will only occur in nature when populations have plenty of
food and space, and little to no competition or predators
What limits population growth?
 The carrying capacity of an ecosystem for a particular species
is the maximum population that the ecosystem can support
indefinitely
What limits population growth?
 A species reaches its carrying capacity when it consumes a
particular natural resource at the same rate at which the
ecosystem produces the resource
 That resource is called a limiting resource
Two Types of Populations Regulation
 Population size can be limited that may or may not be
dependent on the population density
 Density dependent: deaths occur more quickly in a crowded
population; limited resources, predation and disease
 Density independent: portion of the population dies
regardless of the population’s density; severe weather,
natural disasters
How Species Interact with
Each Other
Section 2
Ways in which species interact
Symbiosis
A relationship in which two species live in close association,
typically one species will benefit from the relationship
An Organism’s Niche
 Niche:
 A species’ physical home
 The environmental factors necessary for the species’ survival
 All of the species’ interactions with other organisms
 Habitat: is a location only.
Ways in which species interact
4. Mutualism
A close relationship between two species in which each
species provides a benefit to the other
Ways in which species interact
Competition: a relation in which different individuals or
populations attempt to use the same limited resource
1.
•
•
Intraspecies competition – among members of the same
species (occupy the same niche)
Interspecies competition – among members of different
species (niches overlap)
Ways in which species interact
2. Predation:
An organism that feeds on another organism is called a
predator
The organism that it feeds on is called prey
Ways in which species interact
3. Parasitism:
An organism that lives in or on another organism and feeds
on it is a parasite
Ways in which species interact
5. Commensalism
A relationship in which one species benefits and the other
species is neither harmed nor helped is called commensalism