This document discusses energy flow and population dynamics in ecosystems. It explains that autotrophs (producers) obtain energy from sunlight or inorganic substances to produce food, while heterotrophs (consumers) and decomposers obtain energy by consuming other organisms or their remains. Energy flows through food chains and webs with each step representing a trophic level. Population sizes are influenced by density-independent factors like weather and human impacts, as well as density-dependent factors like competition and disease. Populations can grow exponentially until limiting factors cause logistic growth leveling off at the environment's carrying capacity.

1. Energy Flow and Populations

2. Energy in an Ecosystem
 Autotrophs (Producers)
Flow of Energy in an Ecosystem
 Organism that collects energy from sunlight
or inorganic substances to produce food
 Heterotrophs
(Consumers)
 Organism that
gets it energy
requirements by
consuming other organisms
A lynx is a heterotroph.

3. and return nutrients
to the soil, air,
and water where
the nutrients can
be reused by
organisms.
 Decomposers eat fragments of dead matter
in an ecosystem,
Fungus
Flow of Energy in an Ecosystem
Also known as Detritivores

4. Models of Energy Flow
 Food chains and food webs model the
energy flow through an ecosystem.
 Each step in a food chain or food web is
called a trophic level.
 Producers
 Primary Consumers
 Secondary Consumers
 Tertiary Consumers
Flow of Energy in an Ecosystem
Tertiary
Consumers
Secondary
Consumers
Primary Consumers
Producers

5. Food Chains
 A food chain is a
simple linear model
that shows how
energy flows through
an ecosystem.
 The length of a Food
chains varies with
each ecosystem.
Flow of Energy in an Ecosystem

6. Food Webs
 A food web is a
model representing
the many
interconnected food
chains and pathways
in which energy flows
through a group of
organisms.
Flow of Energy in an Ecosystem

8. Ecological Pyramids
 A diagram that can show the relative
amounts of energy, biomass, or numbers of
organisms at each trophic level in an
organism
 90% of energy is lost as heat
 10% is available energy
Flow of Energy in an Ecosystem

9. Population Density
 The number of organisms of a certain
species per unit area
Population Dynamics

10. Population Dynamics
Common
dolphin
Pupfish
 A species might not be
able to expand its
population range
because it cannot survive
the abiotic conditions
found in the expanded
region.
Population Ranges

11. Population-Limiting Factors
Population Dynamics
 There are two categories of limiting
factors—density-independent factors and
density-dependent factors.

12. Density-Independent Factors
 Any factor in the environment that
does not depend on the number of
members in a population per unit area
is a density-independent factor.
 Weather events
 Fire
 Human alterations of the landscape
 Air, land, and water pollution
Population Dynamics

13. Density-Dependent Factors
 Any factor in the environment that depends
on the number of members in a population
per unit area is a density-dependent
factor.
 Biotic factors
 Disease
 Competition
 Parasites
Population Dynamics

14. Population Growth Rate
 The population growth rate (PGR)
explains how fast a given population
grows.
Population Dynamics

15. Exponential Growth Model
 Exponential growth
occurs when the
growth rate is
proportional to the
size of the
population.
 All populations grow
exponentially until
some limiting factor slows the population’s
growth.
Population Dynamics

16. Logistic Growth Model
 The population’s
growth slows or
stops following
exponential growth,
at the population’s
carrying capacity.
Population Dynamics

17. Population Dynamics
 A population stops increasing when the
number of births is less than the number
of deaths or when emigration exceeds
immigration.

18. Carrying Capacity
 The maximum number of individuals in a
species that an environment can support
for the long term is the carrying capacity.
 Carrying capacity is limited by the energy,
water, oxygen, and nutrients available.
Population Dynamics