Download BioMolecules continued

The energy of the
entire system (Ch.
37)
Population
• A population is a group of individuals of a single species
that occupy the same general area
• Density and dispersion patterns are important population
variables. Population density is the number of individuals
of a species per unit area or volume.
• Environmental and social factors influence the spacing of
individuals in various dispersion patterns
• Clumped
• Uniform
• Random
Yum, plenty of lunch in
this random population
How does a population grow
• A population is defined by how it grows. Multiple
factors may limit population growth.
– Population growth is density dependent (how many
individuals exist in the population).
– Birth rates decline and death rates rise in response to
increasing population density.
– Organisms compete for limited resources
– Density affects health of organisms
– Abiotic factors may limit population growth before limiting
factors become important
• Some populations have "boom-and-bust"
cycles
– Some populations fluctuate in density with
regularity
Example: snowshoe hare and lynx cycles
Hare population size
(thousands)
160
120
Lynx
1850
1875
1900
Year
9
80
6
40
3
0
0
1925
Lynx population size
(thousands)
Snowshoe hare
Structural features of communities
A community includes all the organisms inhabiting a
particular area
•
•
Biological community: an assemblage of all the populations of
organisms living close enough together for potential
interaction
Key characteristics of a community
Species diversity: variety of different kinds of
organisms
Species richness
Relative abundance
Dominant species
Response to disturbances
Trophic structure: feeding relationships among species
Trophic structure is a key factor in community
dynamics.
• Trophic structure: a pattern of feeding
relationships consisting of several different
levels
• Food chain: sequence of food transfer up the
trophic levels. Moves chemical nutrients and
energy
• Producers
–Autotrophs that support all other trophic
levels
–Plants on land
–In water, mainly photosynthetic protists
and cyanobacteria
• Primary consumers
–Herbivores that eat plants, algae, or
phytoplankton
• Secondary, tertiary, and quaternary consumers
– Eat consumers from the level below them
• Detritivores (decomposers)
– Animal scavengers, fungi, and prokaryotes
– Derive energy from detritus produced at all trophic
levels
– Decomposition is essential for recycling nutrients in
ecosystems
Trophic level
Quaternary
consumers
Killer whale
Hawk
Tertiary
consumers
Snake
Tuna
Secondary
consumers
Herring
Mouse
Primary
consumers
Zooplankton
Grasshopper
Producers
Plant
A terrestrial food chain
Phytoplankton
An aquatic food chain
Food chains interconnect, forming food webs
• A food web is a more realistic view of trophic
structure
– Consumers usually eat more than one type of food
– Each food type is consumed by more than one type
of consumer
Quaternary,
tertiary,
and secondary
consumers
Tertiary
and
secondary
consumers
Secondary
and
primary
consumers
Primary
consumers
Producers
(plants)
Ecosystem structure and
dynamics
Ecosystem ecology emphasizes energy flow
and chemical cycling
• An ecosystem consists of all the organisms in
a community and the abiotic factors with which
they interact
• Ecosystem dynamics involve two processes
– Energy flow through the components of the
ecosystem
– Chemical cycling within the ecosystem
LE 37-11
Chemical
cycling
Energy
flow
Chemical
energy
Light
energy
Heat
energy
Chemical elements
Primary production sets the energy budget for
ecosystems
• Primary production: amount of solar energy
converted by producers to chemical energy in
biomass
– Biomass: amount of organic material in an
ecosystem
– Net primary production: amount of biomass
produced minus amount used by producers in
cellular respiration
– Varies greatly among ecosystems
Open ocean
Estuary
Algal beds and coral reefs
Desert and semidesert scrub
Tundra
Temperate grassland
Cultivated land
Boreal forest (taiga)
Savanna
Temperate deciduous forest
Tropical rain forest
0
500
1,000
1,500
2,000
Average net primary productivity (g/m2/yr)
2,500
Energy supply limits the length of food chains
• Only about 10% of the energy stored at each
trophic level is available to the next level
• Pyramid of production shows loss of energy
from producers to higher trophic levels
• Amount of energy available to top-level
consumers is relatively small
• Most food chains have only three to five levels
Tertiary
consumers
Secondary
consumers
Primary
consumers
10 kcal
100 kcal
1,000 kcal
Producers
10,000 kcal
1,000,000 kcal of sunlight
CONNECTION
A production pyramid explains why meat is a
luxury for humans
• Human meat or fish eaters are tertiary or
quaternary consumers
• Humans eating grain have ten times more
energy available than when they process the
same amount of grain through meat
• Using land to raise animals consumes more
resources than using the land to cultivate
crops
Trophic level
Human
meat-eaters
Secondary
consumers
Primary
consumers
Human
vegetarians
Corn
Producers
Cattle
Corn