Download community - Zanichelli online per la scuola

David Sadava, David M. Hillis,
H. Craig Heller, May R. Berenbaum
La nuova
biologia.blu
Le cellule e i viventi
Community and Population
Ecology
What Are Ecological Communities?
An ecological community consists of all the
species that coexist and interact in a defined
area.
What Are Ecological Communities?
A food chain depicts who eats whom in a community.
Food chains are interconnected to make a more
realistic depiction of community feeding relationships,
called a food web.
What Are Ecological Communities?
An organism’s trophic level indicates where in the
food chain it obtains its energy.
What Are Ecological Communities?
Communities are characterized by:
1. Species composition — the number and kinds
of species they contain.
2. The relative abundances of those species.
Communities can be characterized by the distribution
of energy and biomass within them.
What Are Ecological Communities?
At each trophic level energy is lost to metabolism and
respiration.
Only 10% of
energy of one
trophic level is
transferred to the
next level.
Energy and Biomass Distributions
Ecological efficiency: overall transfer of energy from
one trophic level to the next (ratio of consumer
production to producer production).
Pyramid diagrams show
energy, biomass or numbers
of individuals at each trophic
level.
What Are Ecological Communities?
Gross primary productivity (GPP) is the rate at which
primary producers turn solar energy into stored
chemical energy via photosynthesis.
Net primary productivity (NPP) is the rate at which
energy is incorporated into primary producers by
growth and reproduction.
NPP = GPP – R
R = energy lost through respiration
How Does Energy Flow Through the Global Ecosystem?
Different types of ecosystems have different rates
of production.
Geographic Variation in Terrestrial and Marine NPP
How Do Specific Nutrients Cycle through the Global Ecosystem?
The patterns of movements of elements
around the planet are called
biogeochemical cycles.
Properties of biogeochemical cycles
depend on the physical and chemical
nature of each element and how it is
used by organisms.
Biogeochemical Cycles: Hydrologic Cycle
The hydrologic cycle is the cycling of water
through the global ecosystem.
The sun powers the
hydrologic cycle by
causing evaporation
from the ocean
surfaces.
More water is
evaporated from the
oceans than is returned
by precipitation. The
excess falls as
precipitation on land.
Biogeochemical Cycles: Nitrogen Cycle
N2 gas makes up 78% of the atmosphere, but
most organisms cannot use N in this form.
Some bacteria can
convert N2 into a
form usable by plants
(nitrogen fixation).
Other
microorganisms
carry out
denitrification,
returning N2 to the
atmosphere.
Biogeochemical Cycles: Carbon cycle
CO2 is taken up from
the atmosphere by
autotrophs and
incorporated into
organic molecules by
photosynthesis.
Carbon is returned to
the atmosphere by the
metabolism of
organisms.
Biogeochemical Cycles: Carbon cycle
CO2 is being released into the atmosphere faster than
it can be dissolved in oceans and taken up by
organisms.
Biogeochemical Cycles: Phosphorus cycle
Phosphorus is an essential nutrient for DNA,
RNA, ATP, and phospholipids.
It lacks a gaseous
phase. There is
very little in the
atmosphere.
Phosphorus cycles
rapidly in
organisms, but
very slowly in
Earth’s crust.
Biogeochemical Cycles: Sulfur cycle
Emissions of SO2 and H2S from volcanoes and
fumaroles are the only non-microbial sources of
S in the atmosphere.
Microbial decomposition in marine and terrestrial
environments returns S to the atmosphere.
Burning fossil fuels contributes SO2 to the
atmosphere, where it can form sulfuric acid
(H2SO4).
Acidification Reduces Fish Species Richness
Sulfuric and nitric acid (HNO3) form
acid precipitation.
How Do Interactions among Species Influence Communities?
Habitat: the space where organisms live.
Ecosystem engineers: organisms that influence the
ecosystem structure.
A species that exerts influence on a community that is
out of proportion with its abundance is called a
keystone species.
They may influence number
of species and the number
of trophic levels.
How Do Interactions among Species Influence Communities?
A species’ niche is the set of physical and
biological conditions it needs to survive, grow, and
reproduce.
Competitive
exclusion
principle: no
two species can
share the same
limiting resource
indefinitely.
How Do Disturbances Affect Ecological Communities?
Patterns of change in community composition
following disturbance is called succession.
Primary
succession
begins after a
disturbance that
removes all
organisms and
exposes bare
substrate.
How Do Disturbances Affect Ecological Communities?
Secondary succession occurs following
disturbances in which some organisms survive.
How Do Ecologists Measure Populations?
A population consists of individuals of a
species that interact with one another within
a given area at a particular time.
To study populations, ecologists count
individuals, determine their ages, and
calculate the rates at which individuals enter
and leave the population.
The number of individuals per unit area or
volume is the population density.
Dispersion Patterns
Dispersion: distribution of individuals in space.
Dispersion determines
patterns of interaction
among individuals.
How Do Ecologists Measure Populations?
The study of population processes is known as
demography.
Demographic events: births, deaths, immigration,
and emigration.
How Do Ecologists Measure Populations?
To study populations, ecologists count individuals,
determine their ages, and calculate the rates at
which individuals enter and leave the population.
Individuals are
often tagged or
marked in some
way to facilitate
counting.
How Do Ecologists Measure Populations?
Population sizes are often estimated from
representative samples using statistical methods.
Individuals may be counted within measured areas
called quadrats and plants are often counted along a
linear transect.
The mark–recapture method involves capture,
marking, and releasing some individuals, then later
capturing another
sample
of individuals.
What Factors Limit Population Densities?
All populations have the
potential for exponential
growth.
Carrying capacity (K) is
the number of individuals of
a species that can be
supported in an environment
indefinitely.
This pattern is called
logistic growth— S-shaped
curve.
What Factors Limit Population Densities?
Some species achieve higher population densities than
others. Three factors influence this:
• Abundance of
resources
• Body size
• Complex social
organization.
Density-dependent
regulation factors.
Density-independent
factors.
Two Life History Strategies
What Types of Interactions Do Ecologists Study?
Interactions among species can be placed into five
broad categories.
How Do Antagonistic Interactions Evolve?
Prey species have many defenses, including running
away or staying motionless to avoid detection.
Morphological defenses
include shells, tough skin,
spines, and hair.
Chemical defenses are
common in small or weak
prey and sessile
organisms.
How Do Antagonistic Interactions Evolve?
Prey species that are toxic may advertise the fact with
bright coloration or warning signs: aposematism or
warning coloration.
Some prey
species are
mimics.
Adapted from
Life: The Science of Biology, Tenth Edition, Sinauer Associates, Sunderland, MA, 2014
Inc. All rights reserved