1. Population Responses to Environmental Stress
Ecosystems
Population Responses to Environmental Stress

2. Ecosystems Response to Environmental Stress
Homeostasis - the maintenance of favorable internal conditions in a system despite flucutations in external conditions

3. Ecosystems Response to Environmental Stress
Feedback Loop - a circuit of sensing, evaluating, and reacting to changes in environmental conditions as a result of information fed back into a system

4. Ecosystems Response to Environmental Stress Feedback Loop
Positive Feedback - a runaway cycle in which a change in a certain direction provides information that causes a system to change further in the same direction

5. Ecosystems Response to Environmental Stress Feedback Loop
Negative Feedback - a cycle in which a change in a certain direction leads to a lessening of that change

6. Ecosystems Response to Environmental Stress Ecosystem Disturbance
Natural Changes
Catastrophic Changes
Drought
Flood
Earthquake
Disease

7. Ecosystems Response to Environmental Stress Ecosystem Disturbance
Natural Changes
Gradual Changes
Climate change
Immigration
Evolution

8. Ecosystems Response to Environmental Stress Ecosystem Disturbance
Human-Caused Changes
Catastrophic
Deforestation
Plowing
Pesticides
Fires

9. Ecosystems Response to Environmental Stress Ecosystem Disturbance
Human-Caused Changes
Gradual
Salinization
Soil compaction
Depletion of groundwater
Tourism

10. Ecosystems Response to Environmental Stress Ecosystem Stability
Inertia
Constancy
Resilience

11. Ecosystems Response to Environmental Stress Ecosystem Stability
Inertia - ability of a living system to resist being disturbed or altered
Constancy - ability of a living system to maintain a certain size
Resilience - ability of a living system to rebound from an external disturbance

12. Ecosystems Response to Environmental Stress Ecosystem Stability
Do ecosystems have to have high inertia and high resilience to be considered “stable”?
Most ecosystems lack high inertia and resilience

13. Ecosystems Response to Environmental Stress Signs of Ecosystem Illness
Drop in NPP
Increased loss of nutrients
Decline in indicator species
Increased populations of pest species
Decline in species diversity
Presence of toxic chemicals

14. Ecosystems Response to Environmental Stress
Homeostasis and Time Delays
Time delays between input of a stimulus and the corresponding response
Ozone depletion
Global warming
CO2 scrubbing

15. Ecosystems Response to Environmental Stress Homeostasis and Synergy
Synergistic Reaction - a reaction that occurs when two or more processes interact so that the combined effect is greater than the sum of their separate effects

16. Ecosystems Response to Environmental Stress Homeostasis and Synergy
Synergistic Reactions
Beneficial [CO2 and photosynthesis]
Harmful [ozone depletion + global warming]

17. Ecosystems Response to Environmental Stress
Species Diversity and Ecosystem Stability
Ecosystems with higher species diversity have higher NPP and are more resilient
Biodiversity provides “insurance” against catastrophe

18. Ecosystems Response to Environmental Stress
Species Diversity and Ecosystem Stability
Ecosystems with higher species diversity have higher NPP and are more resilient
Biodiversity provides “insurance” against catastrophe

19. Ecosystems Response to Environmental Stress
Species Diversity and Ecosystem Stability
Tropical Rain Forests
High species diversity
High inertia
Low resilience
Most nutrients stored in vegetation

20. Ecosystems Response to Environmental Stress
Species Diversity and Ecosystem Stability
Grasslands
Low species diversity
Low inertia
Burn very easily
High resilience
Most biomass is underground

21. Ecosystems Response to Environmental Stress
Population Responses to Stress
Population Dynamics - the major abiotic and biotic factors that tend to increase or decrease the population size and the age and sex composition of a species

22. Ecosystems Response to Environmental Stress
Population Responses to Stress
Population Dynamics
Size
Density - number of individuals per area)
Dispersion - spatial distribution of species in their habitat

23. Ecosystems Response to Environmental Stress
Population Responses to Stress
Population Dynamics
Biotic Potential - the maximum rate at which a population could grow if it had unlimited resources
Environmental Resistance - all factors that act to limit the growth a population

24. Ecosystems Response to Environmental Stress
Population Responses to Stress
Population Dynamics
Carrying Capacity - the number of individuals of a given species that can be sustained indefinitely in a given area

25. Ecosystems Response to Environmental Stress
Population Responses to Stress
Population Dynamics
Factors influencing carrying capacity
Interspecific and intraspecific competetion
Immigration
Emigration
Catastrophic events
Food and water supply
Habitat

26. Ecosystems Response to Environmental Stress
Population Density and Population Growth
Density-Dependent Population Controls
Increase in significance as population size increases
Competition for resources
Predation
Parasitism

27. Ecosystems Response to Environmental Stress
Population Density and Population Growth
Characteristics of dense populations:
Low birth rates
Slow growth rates
High death rates

28. Ecosystems Response to Environmental Stress
Population Density and Population Growth
Density-Independent Population Controls
Affect a population’s size regardless of size
Natural disasters
Deforestation
Spraying of pesticides

29. Ecosystems Response to Environmental Stress
Population Density and Population Growth
Reproductive Strategies for Survival
r-strategists
K-strategists

30. Ecosystems Response to Environmental Stress
Population Density and Population Growth
Survivorship Curves
Show number of survivors of each age group for a particular species
Late Loss
Constant Loss
Early Loss