Transcript Slide 1

Community. All the organisms of all the species inhabiting an area.
Plant communities apparently determined by chance occurrence of
species with similar requirements. Unclear in animal communities.
The properties and structure of a community are defined by its
species composition and the interactions between the species.
Interspecific Interactions
Competition: -/Predation (includes herbivory and parasitism): +/Mutualism: +/+ (obligatory or facultative= facilitation)
Commensalism: +/0
Key in shaping communities: competition, predation and mutualism.
Species interactions involved in determining trophic structure,
dominant and keystone species, and community control. All affect
community structure.
Trophic structure. Feeding relationships between organisms.
Food chain, trophic levels and food web. Food webs have few
trophic levels: energetic and dynamic stability hypotheses.
Dominant species. Control in community due to abundance.
Keystone species. Control in community due to ecological role.
Community organization.
Bottom-up model. Changes in community structure controlled
by bottom trophic levels (competition and available food).
Top-down model. Changes in community structure controlled
by upper trophic levels (predation).
Communities are dynamic, constantly changing, due to disturbance.
Humans are the greatest agents of disturbance.
Ecological succession- Transitions in species composition over
ecological time.
Primary succession- It begins in a virtually lifeless area where soil
has yet not formed.
Secondary succession- Occurs where an existing community has
been cleared by some disturbance that leaves the soil intact.
Question from February 22nd
1- Wouldn’t ash and other material be nutrient-rich and counted as
soil, therefore making it secondary succession?
Chapter 54
Ecosystem Ecology
Organismal
ecology
coping
Population
ecology
limiting factors
Community ecology
interspecific interactions and diversity
Ecosystem ecology
energy flow and chemical cycling
Landscape ecology
effects on interactions at lower levels
Biosphere ecology
global effects
Ecosystem Ecology
Ecosystem. All the organisms living in a community AND the abiotic
factors with which they interact.
The most inclusive ecosystem is
the biosphere or whole-Earth
ecosystem.
PaleoProject
NASA
page 1198
ECOSYSTEM DYNAMICS
1- Energy flows through ecosystems.
2- Matter cycles within ecosystems. (DECOMPOSERS)
All trophic levels are
connected by decomposition.
Without decomposition life
on Earth would stop.
Tertiary consumers, etc.
1st Law of Thermodynamics
Energy is conserved, it can
only be transformed.
2nd Law of Thermodynamics.
Energy transformation is
inefficient, some lost as heat.
PHOTO, chemo
Elements are not lost, but move through
trophic levels and ecosystems.
Fig. 54.1
pages 1199-1200
ENERGY FLOW
Primary Production. Light energy converted to chemical energy
(organic compounds) by an ecosystem’s autotrophs in a given
period of time (1% converted). Sets Ecosystem’s Energy Budget.
Energy per unit area per unit time (J/m2/ yr) OR Biomass (dry
weight) of organic molecule per unit area per unit time (gC/m2/ yr).
pages 1200-1201
Fig. 54.3
Gross Primary Production (GPP) = Total Primary Production (amount
of light energy converted to chemical energy per unit time)
Some used as fuel for cellular respiration, then:
Net Primary Production (NPP) = GPP – R (as little as 25% of GP in forests)
Only NPP is available to consumers.
Ocean: 46%; Land: 54%
pages 1200-1201
Fig. 54.4
Fig. 54.5
pages 1201-1205
Nutrition addition experiment
Fig. 54.9
Secondary Production
Amount of chemical energy in consumer’s food converted to new
chemical energy in a given period of time.
At individual level:
Detritivores
Production efficiency= fraction of food
energy that is not used for respiration.
Heat
Fig. 54.10
page 1206
PE= 1-3%
PE= 10%
PE= 40%
Trophic Efficiency
Percentage of production transferred from one trophic level to the next.
Values are 5-20% depending on ecosystem. Thus, 80-95% of energy
is lost; loss is multiplied in each trophic level, forming a pyramid.
~10%
Idealized pyramid
of net production
~10%
~10%
~1%
Fig. 54.11
page 1206
Consequence of trophic
efficiencies: total dry weight
of all organisms (standing
crop) diminishes with each
successive trophic level.
(pyramid of biomass).
Some aquatic ecosystems
have inverted pyramids.
Fig. 54.12
Predators usually
larger than prey, so
limited biomass in
upper thropic levels
formed by a small
number of large
individuals (pyramid
of numbers).
pages 1206-1208
Fig. 54.13
Herbivores consume a small percentage of the plant biomass
(globally, <17% of the annual plant production).
The green world hypothesis
Several factors keep herbivores in check:
-Plant defenses: toxins, spines, mutualistic invertebrates, etc.
-Not all essential nutrients plenty available: organic nitrogen.
-Abiotic factors limit herbivores.
-Intraspecific competition: density-dependence.
-Interspecific interactions: predation, parasitism and diseases.
page 1208
Life on Earth depends on the recycling of essential chemical elements.
General
model of
nutrient
cycling
Biological and
geological
processes move
nutrients in the
ecosystem.
pages 1208-1209
Fig. 54.15
Water cycle is driven globally by solar energy.
+
pages 1210
+
Fig. 54.16
The Carbon cycle is defined by the reciprocal processes of
photosynthesis and cellular respiration.
+
balanced
pages 1210
Fig. 54.17
Nitrogen enters ecosystem by atmospheric deposition and nitrogen
fixation by prokaryotes. MOST of nitrogen cycling involves local
processes between organisms and soil or water.
pages 1210-1211
Fig. 54.18
Generalized scheme of
biogeochemical cycles
Decomposition rates
determine the rates of
nutrient cycling.
pages 1212-1213
Fig. 54.20
Nutrient cycling is strongly regulated by vegetation. When plants are
not present, nutrients are lost from the system.
Fig. 54.21
pages 1213-1214
Ohio reservoir
Gizzard shad
Ecologists are recognizing the need
of understanding how landscapes
(comprise different ecosystems) and
food webs interact.
Bioscience 2005