ricklefs_lecture_ppt_ch16 - Rick Relyea Robert Ricklefs The...

The Economy of Nature
7th edition
Lecture PowerPoint
Chapter 16
Competition
Rick Relyea · Robert Ricklefs
© 2014 by W. H. Freeman and Company

Chapter 16 concepts
Competition occurs when individuals experience limited
resources.
The theory of competition is an extension of logistic
growth models.
The outcome of competition can be altered by abiotic
conditions, disturbances, and interactions with other species.
1
2
3
Competition can occur through exploitation or direct
interference, or it may be apparent competition.
4

Types of competition
1
Intraspecific competition: competition among individuals of the
same species.
Negative density dependence is a common type of intraspecific
competition, where an increase in a population’s density causes a
decline in the growth rate of the population.
Interspecific competition: competition among individuals of different
species.
Interspecific competition can cause the population of one species to
decline and eventually die out.

The role of resources
1
Resource: anything an organism consumes or uses that causes an
increase in population growth rate when it becomes more available.
Ecological factors that cannot be consumed (e.g., temperature) are
not considered resources.
Resources for plants can include sunlight, water, and soil nutrients.
Resources for animals can
include food, water, and space.
Example:
Mussels and barnacles in the intertidal
zone compete for space on rocks.
As space decreases, the growth and
fecundity of adults declines.

The role of resources
1
Renewable resources: resources that are constantly regenerated
(e.g., seeds, sunlight).
Nonrenewable resources: resources that are not regenerated (e.g.,
space).
Renewable resources can originate from inside or outside the
ecosystem in which competitors live (e.g., dead leaves fall into
streams from the surrounding forest).
Resources from outside the system do not respond to the rate of
resource consumption.
In contrast, competitors can affect the supply of resources and
demand for resources that originate within the ecosystem.

Leibig’s law of the minimum
1
Not all resources limit consumer populations.
Leibig’s law of the minimum: law stating
that a population increases until the supply
of the most limiting resource prevents it
from increasing further.
Example:
Silica is a limiting resource for diatoms, such
as Asterionella formosa and Synedra ulna .
The two species have different demands
of this limiting resource.
Asterionella populations reach carrying
capacity when they draw silica down to 1μM.
Synedra populations reach carrying capacity
when silica goes down to 0.4μM.

Leibig’s law of the minimum
1
When Synedra reaches carrying
capacity, the abundance of silica in
the environment is not sufficient to
support the population of
Asterionella .