1

Dynamics of Ecosystems

Chapter 57

2

Flow of Energy in Ecosystems

• First Law of Thermodynamics: energy is neither created nor destroyed; it changes forms

• Second Law of Thermodynamics: whenever organisms use chemical-bond or light energy some is converted to heat (entropy)

• Sun our major source of energy (E)

3

• Trophic levels: level an organism “feeds” at

• Producers (autotrophs): “self-feeders” make organic compounds (photosynthesis)

• Consumers (heterotrophs): must take in food

Flow of Energy in Ecosystems

4

• Consumers are classified by their diet

• Herbivores: first consumer level, eat plants• Primary carnivores: eat herbivores• Secondary carnivores: eat primary

carnivores or herbivores• Detritivores: eat decaying matter–Decomposers: microbes that break up

dead matter – “CHONPS”

Flow of Energy in Ecosystems

5

Trophic levels within an ecosystem

6

• Productivity: the rate at which the organisms in the trophic level collectively synthesize new organic matter

• Primary productivity: producers• Respiration: rate producers use org. compounds• Net primary productivity (NPP) = PP – respiration

• Secondary productivity: productivity of a heterotroph trophic level

Flow of Energy in Ecosystems

7

• biomass: the amount of organic matter present at a particular time

• Only small fraction of incoming solar energy is captured by producers ~ 1%/year– Used to make chemical-bond energy– As energy passes up the food chain, most is

lost as heat and waste– Less biomass/fewer individuals at each

trophic level

Flow of Energy in Ecosystems

8

• 50% of chemical-bond energy is not assimilated and is egested in feces

• 33% of ingested energy is used for cellular respiration

• 17% ingested energy is converted into insect biomass

Flow of Energy in Ecosystems

9

10

Flow of energy through the trophic levels of Cayuga Lake

Flow of Energy in Ecosystems

11

• Biomagnification: becomes more concentrated at higher trophic levels

• predatory bird species’ eggshells so thin that the shells broke during incubation

Human Impacts: Pollution

12

13

Ecosystem productivity per year

14

• Trophic level interactions– Trophic cascade: process by which effects

exerted at an upper level flow down to influence two or more lower levels

– Top-down effects: when effects flow down– Bottom-up effects: when effect flows up through

a trophic chain

Flow of Energy in Ecosystems

15Trophic cascade in a large-scale ecosystem

Flow of Energy in Ecosystems

16

• Human removal of carnivores produces top-down effects– Over fishing of cod - 10% their previous numbers– Jaguars and mountain lions absent on Barro

Colorado Island– Smaller predators become abundant

Example: Top-down

17

• When primary productivity is low, producer populations cannot support herbivore populations

• As primary productivity increases, herbivore populations increase

• Increased herbivore populations lead to carnivore populations increasing

Example: bottom-up

18Bottom up effects

Flow of Energy in Ecosystems

19

• Species richness is influenced by ecosystem characteristics–Primary productivity–Habitat heterogeneity• Accommodate more species

–Climatic factors

Biodiversity and Stability

20

Factors that affect species richness

Biodiversity and Stability

21

• Tropical regions have the highest diversity–Species diversity cline: biogeographic

gradient in number of species correlated with latitude – Evolutionary age of tropical regions– Increased productivity– Stability/constancy of conditions–Predation– Spatial heterogeneity

Biodiversity and Stability

22Latitudinal cline in species richness

Biodiversity and Stability