1. Environmental Science: Toward A Sustainable Future Chapter 4
Ecosystems Part 1:
Populations and Succession

2. Lessons Learned in this Chapter
How biotic potential and environmental resistance control population growth.
Ecological succession: primary, secondary and aquatic.
The third and fourth principles of ecosystem sustainability. (predators preventing overgrazing and ecosystem resilience)
How humans influence the rate and direction of ecosystem change.

3. Outline of Chapter 4 Population dynamics Population equilibrium
Inter and Intraspecies Competition
Succession
Living beyond our means
Natural Selection and Evolution

4. Population Growth = B – D + I - E
Dynamic Equilibrium
Births
Deaths
A balance between births (B) and deaths (D), along
with a balance between immigration (into a pop, I) and
emigration (movements out of a population, E).
Population Growth = B – D + I - E

5. Population Growth Curves
Not sustainable
= K

7. Biotic Potential
Biotic potential: the number of possible offspring produced under optimal conditions due to
Reproductive rate
Migration and dispersal abilities
Defenses
Coping strategies
r = instrinic rate of population growth if had unlimited resources
Critical size = minimum size a population needs to support a breeding population, below this the population is a high risk of becoming extinct

8. Environmental Resistance
combination of biotic and abiotic factors that may limit population increase
Predators, competitors, disease
Adverse weather, limited food/nutrients
Carrying capacity (K on pop curves) is the maximum # of individuals than can be sustained indefinitely in a given space

9. Biotic Potential Vs. Environmental Resistance

10. Reproductive Strategies
r-strategist K-strategist
Populations tend to remain stable near the carrying capacity (K)
Instrinic rate of population growth is high
Many offspring with
low parental care, success
In instable ecosytems
Few offspring with
high parental care,
prone to extinction

11. Population Dynamics Factors of environmental resistance are either:
Density-independent controls effects do not vary with population density: e.g., adverse weather, earthquakes, drought, fire, pesticides, habitat destruction
Density-dependent have a greater effect on a pop as the pop density increases: e.g., infectious disease, overgrazing, predation, parasitism, competition for space

12. Predator-prey Balance:Wolves and Moose on Royal Isle Island

13. Tipping the Balance: Introduced Species (alien species, invasive species, exotic species)
Rabbits in Australia with no natural predators
Domestic cats on islands
Zebra mussels in the Great Lakes
Chestnut blight fungus from Chinese chestnut trees

14. Introduced Species
Why have these introductions resulted in a degradation of the ecosystems? (Think in terms of environmental resistance and biotic potential.)
See text pages 91 to 95 for details on each of these examples

15. The Third Principle of Ecosystem Sustainability
The size of the consumer population is maintained so that overgrazing or other overuse does not occur.
Rabbit overgrazing on Phillip Island

16. Mechanisms of Population Equilibrium: Plant-Herbivore
29 reindeer introduced on St. Mathew Island

17. Mechanisms of Population Equilibrium
Absence of natural enemies like predators allows a herbivore population to exceed carrying capacity which results in overgrazing of the habitat. The herbivore population subsequently crashes.

18. Balanced Herbivory

19. Mechanisms of Population Equilibrium of Herbivores
Can be both predator-prey (top down) or plant-herbivore (bottom up) methods of controlling the size of the herbivore population.
How would the herbivore population growth curve look if diseases were used as the control mechanism?

20. Mechanisms of Population Equilibrium: Plant Diversity
Microclimates (shade of trees or in bright sun, burrows underground, near water edge etc)
Ecological niches: the lifestyles or roles of each species are specialized (specific adaptations)
Balanced herbivory of different types of plant or different parts of same plant

21. Interspecific Competition and Population Equilibrium
Competition between members of different species can be resolved due to specific adaptations, an example is riparian (water related microecosystems) vs. non-riparian
In Great Plains, grasses in most areas yet riparian woodlands along river banks
In Easter US, sycamore and red maple can thrive in water-saturated soil while oaks and pines require well-drained soil

22. More Interspecific Competition Adaptations
Predator-prey relationships in balance…any eating of another species is a predator-prey
Symbiosis (long lasting relationship in which species live together in intimate association
Parasitism: parasite benefits and host is harmed (fungus, protozoan, bacteria, leeches)
Mutualism: both benefit like epiphytes (air growing plants) in rainforest trees or lichens (photosynthetic algae combined with decomposing fungi)
Commensalism: one benefits other is neutral (ferns growing in shade of redwood trees)
Resource Partitioning for food or shelter or breeding

23. Intraspecific (within species) Competition and Population Equilibrium
Territoriality: defense of a resource against individuals of the same species
Examples of wolves and songbirds
Results in priority use of resources for feeding, breeding and living
Self-thinning to maximize resources
In plants physical space is needed
In animals, overcrowded conditions can lead to easier spread of disease, hormone shifts producing less young, cannibalism for survival, etc.

24. Types of Species in an Ecosystem
Native species: normally lives and thrives there
Non-native (exotic, alien): immigration of a species naturally, sometimes an accidental or deliberate introduction by humans
Indicator species: serve as early warnings that a community is damaged, e.g. birds, especially raptors b/c they are quickly effected and trout species present indicate water quality and levels of dissolved oxygen
Keystone species: play pivotal roles in the function and integrity of their ecosystem, e.g. , dung beetles, sea otters with kelp, beavers with beaver pond habitats (46% of endangered animals happen due to lack of beaver ponds), great white shark, elephants in tearing down trees to keep grassland and forest balance

25. Disturbance and Succession
Equilibrium theory: ecosystems are stable environments and there is an ongoing “balance of nature”
Nonequilibrium theory points out that the “patchiness” of nature within ecosystems indicate ecosystem are always shifting and changing, e.g. due to abiotic distrubances, climate shifts etc

26. Succession – One groups of biotic populations gradually replaced by others in an ecosystem
primary – new ecosystem where there were no living things before. Cooled lava, receded glacier, mud slide
secondary- ecosystem used to be there. Fire, humans clear an area
Aquatic – (type of secondary) lakes taken over by terrestrial ecosystem
Climax ecosystem- in balance only changes if major interference
Retreat of a glacier to expose bare rock

27. Primary succession (no soil)
Must create new soil for plants to grow
The first plants to come in are called pioneer species, these include mosses and lichens which collect water, can go dormant in low water situations, and whose acids can break down rock minerals to form soil
Lichen  grass  shrub  pine tree (likes lots of sun and quick grower)  hardwood trees (deciduous trees like oak)  climax ecosystem

28. Primary Succession
Lichens and Mosses invade an area and provide a place for soil and water to accumulate.
Larger plants germinate in the new soil layer resulting in additional soil formation.
Eventually shrubs and trees will invade the area.
First pine (soft wood) then deciduous (hard wood trees) like oaks, hickories, beeches, maples and fruit trees

29. Secondary Succession

30. Aquatic Succession

31. The Fourth Principle of Ecosystem Sustainability
Ecosystems show resilience during a disturbance

32. Disturbance and Resilience (recovery)
Removes organisms
Reduces populations
Releases organic nutrients to the soil in dry climates
Creates opportunities for other species to colonize (lodge pole pine seeds only release in a fire, grasses needs lots of sunlight exposure)

33. Fires in Ecosystem
Maintain balance of species and energy in ecosystems over the long run.
Beneficial b/c provide nutrients for soil
We avoid natural fires, but the problems like Crown Fires- (not natural) kill the whole tree
1988 Yellowstone fires changed climax ecosystems of white bark pine trees to huckle berries. Grizzlies ate both

34. Fire and Succession
Fire climax ecosystems: dependent upon fire for maintenance of existing balance; e.g., grasslands, pine and redwood forests
What significance does this have for humans and where they live?

35. Resilience Mechanisms After A Forest Fire
Nutrient release to soil
Regrowth by remnant roots and seeds
Invasions from neighboring ecosystems
Rapid restoration of energy flow and nutrient cycling

36. Human Impacts: We have…
Increased our biotic potential
Decreased our environmental resistance
Contributed to the degradation of ecosystems
We are still on an unsustainable J curve…uh oh!

37. Human Impacts Introduce species Eliminate natural predators
Alter abiotic factors
Misunderstand the role of fire
Reduce biodiversity

38. Implications For Humans
Protecting and managing the natural environment to maintain the goods and services vital to human economy and survival.
Establishing a balance between our own species and the rest of the biosphere by living in a sustainable way.
Global CPR is needed: conservation, preservation, and restoration
Find ways to create positive feedback loop tipping points like the marine sanctuaries on Apo Island to protect fisheries pg. 108 for details

39. Four Principles of Ecosystem Science
Ecosystems will change over time
Individual species and interactions between species will have important impacts on ecological processes
Different sites and regions are unique (abiotic and biotic characteristics)
Disturbances are important and frequent events that have a profound impact on the ecosystem

40. Fifth Principle of Ecosystem Sustainability
Ecosystems depend on biodiversity.

41. Why is the fifth principle of sustainability important in understanding the following issues?
Endangered species
Agriculture
Biotechnology
Medicine