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Transcript
1
The Web of Life
Chapter 1 The Web of Life
CONCEPT 1.1 Events in the natural
world are interconnected.
CONCEPT 1.2 Ecology is the scientific
study of interactions between
organisms and their environment.
CONCEPT 1.3 Ecologists evaluate
competing hypotheses about natural
systems with observations,
experiments, and models.
Deformity and Decline in Amphibian Populations: A Case Study
There is a high incidence
of deformities in
amphibians.
place fig. 1.1 here
Amphibian
populations are
declining worldwide.
Figure 1.2 Amphibians in Decline
Deformity and Decline in Amphibian Populations: A Case Study
Amphibians are “biological indicators”
of environmental problems.
• Skin is permeable; pollutant
molecules can pass through easily.
• Eggs have no protective shell.
• They spend part of their life on
land and part in water—exposed to
pollutants and UV in both
environments.
Introduction
Humans have an enormous impact on
the planet.
It is important that we try to understand
how natural systems work.
Ecology is the scientific study of how
organisms affect, and are affected by,
other organisms and their
environment.
Concept 1.1
Events in the natural world are
interconnected.
Concept 1.1
Connections in Nature
Even species that do not interact directly
can be connected by shared
environmental features.
Ecologists ask questions about the
natural world in order to understand
these connections.
Concept 1.1
Connections in Nature
Controlled experiment: Experimental
groups are compared with a control
group that lacks the factor being
tested.
Tree frog eggs were exposed to
Ribeiroia parasites in the lab.
Four treatments: 0 (the control group),
16, 32, or 48 Ribeiroia parasites.
Figure 1.4 Parasites Can Cause Amphibian Deformities
Figure 1.5 Do the Effects of Ribeiroia and Pesticides Interact in Nature?
Concept 1.1
Connections in Nature
Hypothesis: Pesticides decrease the
ability of frogs to resist infection by
parasites.
In another lab experiment, tadpoles
reared in the presence of pesticides
had fewer white blood cells
(indicating a suppressed immune
system) and a higher rate of Ribeiroia
cyst formation.
Figure 1.6 Pesticides May Weaken Tadpole Immune Systems (Part 2)
Concept 1.2
Ecology is the scientific study of
interactions between organisms and their
environment.
Concept 1.2
What Is Ecology?
Ecology is the scientific study of
interactions between organisms and
their environment.
Environmental science incorporates
concepts from the natural sciences
(including ecology) and the social
sciences and focuses on how people
affect the environment and how to
address environmental problems.
Concept 1.2
What Is Ecology?
Early ecological views:
1. There is a “balance of nature” in
which natural systems are stable
and tend to return to an original
state after disturbance.
2. Each species has a distinct role to
play in maintaining that balance.
Concept 1.2
What Is Ecology?
Ecologists now recognize that natural
systems do not necessarily return to
their original state after a
disturbance, and seemingly random
perturbations can play an important
role.
Evidence suggests that different
species often respond in different
ways to changing conditions.
Concept 1.2
What Is Ecology?
Scientists now recognize that
ecological interactions are more
complex than previously thought.
One view that has stood the test of
time: Events in nature are
interconnected.
A change in one part of an ecological
system can alter other parts of that
system.
Table 1.1 (Part 1)
Table 1.1 (Part 2)
Figure 1.8 An Ecological Hierarchy
Concept 1.2
What Is Ecology?
Population: A group of individuals of a
species that are living and interacting
in a particular area.
Community: An association of
populations of different species in the
same area.
Ecological studies often include both
the biotic (living) and abiotic
(physical) components of natural
systems.
Figure 1.9 A Few of Earth’s Many Communities
Concept 1.2
What Is Ecology?
Ecosystem: A community of
organisms plus their physical
environment.
Landscapes: Areas with substantial
differences, typically including
multiple ecosystems.
All the world’s ecosystems comprise
the biosphere—all living organisms
on Earth plus the environments in
which they live.
Table 1.2
Concept 1.2
What Is Ecology?
All living systems change over time.
Evolution:
1. Change in genetic characteristics
of a population over time.
2. Descent with modification—
organisms gradually accumulate
differences from their ancestors.
Concept 1.2
What Is Ecology?
Adaptation: A characteristic that
improves survival or reproduction.
Natural selection: Individuals with
certain adaptations tend to survive
and reproduce at a higher rate than
other individuals.
If the adaptation is heritable, the
frequency of the characteristic may
increase in a population over time.
Figure 1.10 Natural Selection in Action
Concept 1.2
What Is Ecology?
Ecosystem processes:
Producers use energy from an
external source (e.g., the sun) to
produce their own food.
Net primary productivity (NPP):
Energy captured by producers minus
the amount lost as heat in cellular
respiration.
Consumers get energy by eating
other organisms or their remains.
Concept 1.3
Ecologists evaluate competing hypotheses
about natural systems with observations,
experiments, and models.
Concept 1.3
Answering Ecological Questions
No single approach works in all
situations, so ecologists use a variety
of methods:
• Observational studies in the field
• Controlled experiments in the
laboratory
• Experiments in the field
• Quantitative models
Concept 1.3
Answering Ecological Questions
Experimental design:
1. Replication—performing each
treatment more than once; reduces
possibility that results are due to a
variable that was not measured or
controlled in the study.
2. Assign treatments at random—also
limits the effects of unmeasured
variables.
Concept 1.3
Answering Ecological Questions
3. Analyze results using statistical
methods; standardized ways to
determine whether observed
differences are significant (great
enough to be of biological
importance).