1. Biodiversity, Species Interactions, and Population Control
Chapter 5

2. 5-1 How Do Species Interact?
Concept 5-1 Five types of species interactions – competition, predation, parasitism, mutualism, and commensalism – affect the resource use and population sizes of the species in an ecosystem.

3. Species
Interactions

4. COMPETITION
Organisms compete for shared or limited resources such as food, water, space, and habitats.
Competitive exclusion principle – No two species can occupy the exact same niche for very long
More in Section 5-2

5. COMPETITION
Interspecific competition is the competition between member of two different species. The result is that neither species can obtain as many resources as they could in the absence of the other species.
Intraspecific competition is the competition between member of the same species.
This also includes the competition for mates.

6. PREDATION Species called predators feed on other species called prey.
Organisms use their senses to locate objects and their prey.
Some predators are fast enough to catch their prey, some hide and lie in wait, and some inject chemicals to paralyze their prey.

7. PREDATION Some prey may escape their predators by: Camouflage
Outer protection
Chemical warfare
Warning coloration
Mimicry
Deceptive looks
Deceptive behavior

8. Predator and Prey Species Can Drive Each Other’s Evolution
Intense natural selection pressures exist between predator and prey populations
Coevolution – changes in the gene pool of one species can lead to changes in another species
Evolution in the predator population – improved abilities to capture prey
Evolutionary response – the prey improves its abilities to avoid capture
The evolution of improved escape abilities should result in increased capture abilities.
Evolutionary “arms race”
The levels of defense and counter-defense will continue to escalate.

9. Parasitism
Parasitism occurs when one species feeds on part of another organism.
Although parasites can harm their hosts, they can promote community biodiversity.
Some parasites live inside the host (micororganisms, tapeworms).
Some parasites live outside the host (fleas, ticks, mistletoe plants, sea lampreys).
Some have little contact with host (cowbirds – lay eggs in another’s nest…let them take care of young.)

10. Parasitism

11. Mutualism
In mutualism, two species interact in a way that benefits both of them.
Most organisms benefit through mutualistic interactions by gaining nutrition or protection.

12. Commensalism
Commensalism is an interaction that benefits one species but has little, if any, effect on the other species.
Epiphytes

13. 5-2 How Can Natural Selection Reduce Competition between Species?
Concept 5-2 Some species develop adaptations that allow them to reduce or avoid competition with other species for resources.

14. 5-2 How Can Natural Selection Reduce Competition between Species?
Niches (way of life) become separated to avoid competition for resources.
Reduce niche overlap
This is also the basis of natural selection – the pressure that drives the evolution of new species.
Chapter 4

15. 5-2 How Can Natural Selection Reduce Competition between Species?
Some species evolve adaptations that allow them to reduce or avoid competition for resources with other species (resource partitioning).
Each species minimizes competition with the others for food by spending at least half its feeding time in a distinct portion of the spruce tree and by consuming somewhat different insect species.

16. 5-2 How Can Natural Selection Reduce Competition between Species?
Genetic variation and specialized feeding niches can lead to evolutionary divergence.
Use shared resources at different:
Times
Places
Ways
Each species has a beak specialized to take advantage of certain types of food resource.

17. 5-3 What Limits the Growth of Populations?
Concept 5-3 No population can continue to grow indefinitely because of limitations on resources and because of competition among species for those resources.

18. Populations Have Certain Characteristics
Populations differ in their:
Distribution
Numbers
Age structure (proportion of individuals in diff. age groups)
Density (number of individuals in a given area)
Population dynamics – the study of changes in population characteristics due to:
Temperature
Presence of disease organisms or harmful chemicals
Resource availability
Arrival or disappearance of competing species

19. Most Populations Live Together in Clumps or Patches
Most populations live in clumps although other patterns occur based on resource distribution.
Clumps can help provide protection, aid in capture of prey, or be for mating or caring for young.

20. No Population Can Grow Indefinitely
Biotic Potential
The intrinsic rate of increase (r) is the rate a population would grow if it had unlimited resources.
Maximum rate of population increase under ideal conditions.
In nature, biotic potentials are rarely reached
Individuals in populations with high r :
Reproduce early in life
Have short generation times
Can reproduce many times
Have many offspring each time they reproduce

21. No Population Can Grow Indefinitely
In general,
Populations with large individuals have a low biotic potential
Humans, elephants, blue whales
Populations with small individuals have a high biotic potential
Bacteria, insects, microorganisms
Examples
Rabbits are sexually mature at 5 months of age. Their gestation period averages 31 days and the average litter size is 6 offspring. It is possible to have 8 litters per year. If we start with 1 fertile female and assume that 0 die and 50 percent of the litter is female, at the end of twelve months we have approximately 1,850 rabbits.
Bacteria populations can double every 20 minutes
For humans, the biotic potential (for females age 14 years to 50 years) can average as high as 12 per female.
Elephants have a 22 month gestation period and can usually only give birth once every 4 years. 21

22. No Population Can Grow Indefinitely
In nature, all rapidly growing populations will eventually reach a size limit imposed by various limiting factors such as:
Light
Water
Space
Nutrients
Competition
Predators
Infectious diseases

23. No Population Can Grow Indefinitely
No population can increase its size indefinitely.
Environmental Resistance – the sum of all the factors that act to limit the growth of a population
Limiting factors can be food, water, light, space, nutrients, competitors, predators, disease, etc.
These factors act as a negative feedback on the population size.
Carrying capacity (K): the maximum population of a given species that a particular habitat can sustain indefinitely without degrading the habitat.

24. No Population Can Grow Indefinitely: J-Curves and S-Curves
Linear Growth
Exponential Growth
We will be using these terms in our population growth discussions
Know them!!
Logistic Growth

25. No Population Can Grow Indefinitely: J-Curves and S-Curves
Populations grow rapidly with ample resources – starts off as exponential growth (J-Curve).
As resources become limited, its growth rate slows and levels off. 25

26. No Population Can Grow Indefinitely: J-Curves and S-Curves
As a population levels off (forming the S-Curve) it often fluctuates slightly above and below the carrying capacity.
This fluctuation can be small, large, regular, or irregular. 26

27. When a Population Exceeds Its Habitat’s Carrying Capacity…
Populations which overshoot their carrying capacity suffer a crash (or dieback)
This situation is made possible by a reproductive time lag
The time needed for birth/death rates to change in response to environmental changes.
Overshooting the carrying capacity can adversely affect the ecosystem as well
Decrease the carrying capacity 27

28. Under Some Circumstances Population Density Affects Population Size
Population density: the number of individuals in a population found in a particular area.
Some population controls are density-dependent. This means that they have a greater effect as the population density increases.
e.g. biotic factors, predation, competition, disease, scarcity of food
Other population controls are density-independent and are not affected by population density.
e.g. abiotic factors like weather, pollution, fire

29. Species Have Different Reproductive Patterns
r-selected species – Large number of smaller offspring with little parental care.
They overcome the massive loss of offspring by having so many that even if only very few survive – it is enough.
Opportunists – reproduce and disperse at a rapid rate (r) when conditions are favorable. 29

30. Species Have Different Reproductive Patterns
K-selected species – Fewer, larger offspring with higher invested parental care.
Produce offspring later in life and put a lot of energy into one offspring.
Competitors – can compete well for resources when the population is close to the carrying capacity (K). 30

31. Species Have Different Reproductive Patterns31

32. Species Have Different Reproductive Patterns
Answer:
R-selected species – they are more adaptive to changing environmental conditions.
Since they have many offspring and much faster, they can also evolve much more quickly. 32

33. Population Change Curves in Nature
Population sizes often vary in regular cycles when the predator and prey populations are controlled by the scarcity of resources.
These populations are regulated through:
Top-down population regulation – predation, parasitism
Bottom-up population regulation – the scarcity of resources

34. -- NOT IN TEXTBOOK -- Survivorship Curves:
The way to represent the age structure of a population is with a survivorship curve.
Late loss population (Type I)
Live to an old age
Humans, elephants
Constant loss population (Type II)
Die randomly at all ages
Most birds
early loss population (Type III)
Most members die at young ages
Fish, amphibians, many insects

35. 5-4 How Do Communities and Ecosystems Respond to Changing Environmental Conditions?
Concept 5-4 The structure and species composition of communities and ecosystems change in response to changing environmental conditions through a process called ecological succession.

36. 5-4 How Do Communities and Ecosystems Respond to Changing Environmental Conditions?
New environmental conditions allow one group of species in a community to replace other groups.
Ecological succession: the gradual change in species composition of a given area
Primary succession: the gradual establishment of biotic communities in lifeless areas where there is no soil or sediment.
Secondary succession: series of communities develop in places containing soil or sediment.

37. 5-4 How Do Communities and Ecosystems Respond to Changing Environmental Conditions?
Primary succession begins with an essentially lifeless area where there is no soil.
The weathering of rocks and the introduction of hearty plants begins to form soil.
Eventually, more and more plant species are able to take hold.
This process takes a very long time.
(100’s -1000’s of years)

38. 5-4 How Do Communities and Ecosystems Respond to Changing Environmental Conditions?
Primary succession begins with an essentially lifeless area where there is no soil.

39. Early successional plant species, pioneer
5-4 How Do Communities and Ecosystems Respond to Changing Environmental Conditions?
Early successional plant species, pioneer
Lichens, mosses
Trap windblown sediments, moisture
Break apart rocks
Midsuccessional plant species
Grasses, low shrubs
Late successional plant species
Mostly trees

40. 5-4 How Do Communities and Ecosystems Respond to Changing Environmental Conditions?
Secondary succession occurs when the natural community has been disturbed, removed, or destroyed.
This disturbance could be as a result of a fire, flood, or humans.
The key is that soil already exists so that this process many only take a years.

41. 5-4 How Do Communities and Ecosystems Respond to Changing Environmental Conditions?
Secondary succession occurs when the natural community has been disturbed, removed, or destroyed.

42. Succession Doesn’t Follow a Predictable Path
The course of succession cannot be precisely predicted.
Traditional view
Balance of nature and a stable climax community will always be achieved.
Current view
Ever-changing mosaic of patches of vegetation
Succession involves species competing for enough light, nutrients and space which will influence it’s trajectory and end result.
State of continual disturbance and change