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

2. Core Case Study: Southern Sea Otters: Are They Back from the Brink of Extinction?
Habitat
Live in giant kelp forests (California, West Coast)
Prey on many kelp-eating shellfish
Hunted: early 1900s
Fur traders
Competition with local shell-fisherman
Partial recovery (still endangered, though)
FWS declared endangered, numbers grew from 50 to 2,654
Why care about sea otters?
Ethics
Tourism dollars
Keystone species
Control population of shellfish that would otherwise exploit the kelp forests

3. Southern Sea Otter
Figure 5.1: An endangered southern sea otter in Monterey Bay, California (USA), uses a stone to crack the shell of a clam (left). It lives in a giant kelp bed (right). Scientific studies indicate that the otters act as a keystone species in a kelp forest system by helping to control the populations of sea urchins and other kelp-eating species.
Fig. 5-1a, p. 104

4. 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.

5. Species Interact in Five Major Ways
Interspecific Competition- members of different species compete for resources
Predation-one species feeds directly on another
Symbiotic Interactions
Parasitism-one species uses a another as a host to gain nutrients in a way that it harms the host. Usually on or in the host
Mutualism- interactions between two different species in which both species benefit from each other
Commensalism- interaction between 2 species where one species benefits and the other is neither helped nor harmed (neutral)

6. Most Species Compete with One Another for Certain Resources
Competition:
Actual fighting
Mostly one species becoming more efficient at gaining resources
Remember every species occupies a special ecological niche
Some niches overlap
When they both require the same resources
The greater amount of shared resources, the more intense competition

7. Overlapping Niches Result in…
When one species is much more efficient at obtaining resources, the other must either:
Move (if possible)
Alter (reduce or shift) its niche through natural selection
Suffer population decline
Become extinct

8. Some Species Evolve Ways to Share Resources
Resource partitioning
Using only parts of resource
Using at different times
Using in different ways

9. Black-throated Green Warbler Yellow-rumped Warbler
These different species of birds feed on different parts of the spruce tree to partition their resources. Some feed on different insect species
Black burnian Warbler
Black-throated Green Warbler
Cape May Warbler
Bay-breasted Warbler
Yellow-rumped Warbler
Figure 5.2: Sharing the wealth: This diagram illustrates resource partitioning among five species of insect-eating warblers in the spruce forests of the U.S. state of Maine. Each species minimizes competition with the others for food by spending at least half its feeding time in a distinct portion (yellow highlighted areas) of the spruce trees, and by consuming somewhat different insect species. (After R. H. MacArthur, “Population Ecology of Some Warblers in Northeastern Coniferous Forests,” Ecology 36 (1958): 533–536.)
Fig. 5-2, p. 106

10. Specialist Species of Honeycreepers
Honeycreepers of Hawaii descended from one common ancestor, now have differentiated in beak shapes to partition their resources
Figure 5.3: Specialist species of honeycreepers: Through natural selection, different species of honeycreepers developed specialized ecological niches that reduced competition between these species. Each species has evolved a specialized beak to take advantage of certain types of food resources.
Fig. 5-3, p. 107

11. Most Consumer Species Feed on Live Organisms of Other Species
Predators capture prey several ways
Herbivores:
Swim, walk, fly up to plants they feed on
Carnivores:
2 options: pursuit and ambush
Cooperative hunting: pack of lions hunting giraffes
Camouflage:
Hide in plain sight and ambush
Examples: praying mantis, snowy owls
Chemical warfare:
Poisonous snakes and spiders (examples)

12. Predator-Prey Relationships
Figure 5.4: Predator-prey relationship: This brown bear (the predator) in the U.S. state of Alaska has captured and will feed on this salmon (the prey).
Fig. 5-4, p. 107

13. Prey species have evolved ways to avoid predators
Exceptional ability to run, swim, fly away
Highly developed senses (sight and smell)
Protective physical features:
Shells
Thick bark
Spines
Thorns
Lizard tails
Break off when attacked and give extra time to escape

14. Prey species have evolved ways to avoid predators
Camouflage
Chemical Warfare
Poison
Irritants
Foul-smelling, bad tasting
Squids, octopus emit ink clouds to confuse predators
Warning coloration
Mimicry
Non-harmful prey that mimic more risky prey
Ex. The Viceroy butterfly looks and acts like monarch which is poisonous
Deceptive looks and behavior
Moths, blow fish

15. (b) Wandering leaf insect
(a) Span worm
(b) Wandering leaf insect
(c) Bombardier beetle
(d) Foul-tasting monarch butterfly
(e) Poison dart frog
(f) Viceroy butterfly mimics
monarch butterfly
(g) Hind wings of Io moth
resemble eyes of a much
larger animal.
(h) When touched,
snake caterpillar changes
shape to look like head of snake.
Stepped Art
Fig. 5-5, p. 109

16. Science Focus: Threats to Kelp Forests
Kelp forests: biologically diverse marine habitat
Extract the substance algin from kelp for use as a renewable resource
Used in toothpaste, cosmetics, ice-cream, and more
Major threats to kelp forests
Sea urchins- feed on kelp
Pollution from water run-off
Global warming

17. Purple Sea Urchin
Figure 5.A: This purple sea urchin inhabits the coastal waters of the U.S. state of California.
Fig. 5-A, p. 108

18. Predator and Prey Interactions Can Drive Each Other’s Evolution
Intense natural selection pressures between predator and prey populations
Both prey and predator evolve adaptations to survive
Coevolution
Definition: when two species interact with each other over a long period of time, changes in the gene pool of one species can lead to changes in the gene pool of the other species.
Interact over a long period of time
Bats and moths: echolocation of bats and sensitive hearing of moths

19. Coevolution: A Langohrfledermaus Bat Hunting a Moth
Fig. 5-6, p. 110

20. Some Species Feed off Other Species by Living on or in Them
Parasitism
Parasite is usually much smaller than the host
Parasite rarely kills the host
Mostly draw nourishment from host and gradually weaken them over time
Parasites may have a negative reputation, but they never-the-less add to species biodiversity
May live inside or outside host
Examples: tapeworms, ticks, sea lampreys, fleas, mistletoe plants

21. Parasitism: Trout with Blood-Sucking Sea Lamprey
Fig. 5-7, p. 110

22. Mutualism Two interacting species benefit each other by doing so
Examples:
Bees/butterflies/mosquitos/hummingbirds and flowering plants (pollination)
Clownfish and sea anenomes
Oxpeckers and black rhinoceros
Gut inhabitant mutualism: beneficial bacteria in digestive systems
Note: mutualism is not a cooperative agreement.
Unintentional benefit by exploiting each other
Each species is in it for themselves

23. Mutualism: Oxpeckers Clean Rhinoceros; Anemones Protect and Feed Clownfish
Fig. 5-9, p. 111

24. Commensalism Examples:
Interaction where one species benefits and the other is neither helped, nor harmed (just neutral)
Examples:
Epiphytes: “air plants” attach themselves to trunks or branches of large trees
Gain better access to sunlight, nutrients; gain a solid base on which to grow
Birds nesting in trees
Bromeliad Epiphyte

25. 5-2 What Limits the Growth of Populations?
Concept 5-2 No population can continue to grow indefinitely because of limitations on resources and because of competition among species for those resources.

26. Most Populations Live Together in Clumps or Patches (1)
Population: group of interbreeding individuals of the same species
Population distribution
Clumping
Uniform dispersion
Random dispersion

27. Most Populations Live Together in Clumps or Patches (2)
Why clumping?
Species tend to cluster where resources are available
Groups have a better chance of finding clumped resources
Protects some animals from predators
Packs allow some to get prey

28. Populations Can Grow, Shrink, or Remain Stable (1)
Population size governed by
Births
Deaths
Immigration
Emigration
Population change =
(births + immigration) – (deaths + emigration)
Negative value means population is shrinking
Positive value means population is growing
0 means stable

29. Populations Can Grow, Shrink, or Remain Stable (2)
Age structure: Distribution of individuals among various age groups in a population
Can have strong effects on how fast a population grows or shrinks
Age groups described as:
Pre-reproductive age
Reproductive age
Post-reproductive age
Population most likely to grow fast the more individuals there are in the reproductive age group

30. Age Structure Graphs
Why is taking gender into account important? Would a population grow faster with more men than women or women than men at reproductive ages? What does this depend on?

31. Some Factors Can Limit Population Size
Range of tolerance
Variations in physical and chemical environment
Some individuals within a population can be slightly more tolerant (see next slide
Limiting factor principle
Too much or too little of any physical or chemical factor can limit or prevent growth of a population, even if all other factors are at or near the optimal range of tolerance
Precipitation
Nutrients
Sunlight, etc

32. Trout Tolerance of Temperature
Figure 5.13: This diagram illustrates the range of tolerance for a population of organisms, such as trout, to a physical environmental factor—in this case, water temperature. Range of tolerance restrictions prevent particular species from taking over an ecosystem by keeping their population size in check. Question: For humans, what is an example of a range of tolerance for a physical environmental factor?
Fig. 5-13, p. 113

33. Limiting Factors control population sizes
Important Land Limiting Factors:
Precipitation/water
Soil nutrients
Temperature
Important Aquatic Limiting Factors
Sunlight
Nutrient availability
Dissolved oxygen levels
Salinity

34. No Population Can Grow Indefinitely: J-Curves and S-Curves (1)
Size of populations controlled by limiting factors:
Light
Water
Space
Nutrients
Exposure to too many competitors, predators or infectious diseases
There will always be limits to population growth
No population can grow indefinitely

35. No Population Can Grow Indefinitely: J-Curves and S-Curves (2)
Environmental resistance
All factors that act to limit the growth of a population
Determines a population’s carrying capacity
Carrying capacity (K)
Maximum population a given habitat can sustain
When populations near the (K), growth RATE begins to slow/decline

36. No Population Can Grow Indefinitely: J-Curves and S-Curves (3)
Exponential growth (J-curve)
Starts slowly, then accelerates to carrying capacity when meets environmental resistance
Logistic growth (S-curve)
Decreased population growth rate as population size reaches carrying capacity

37. Logistic Growth of Sheep in Tasmania
Note how the population size fluctuates, it never truly stabilizes. Overshoot usually occurs, knocks the population back down, and up again.
Figure 5.15: This graph tracks the logistic growth of a sheep population on the island of Tasmania between 1800 and After sheep were introduced in 1800, their population grew exponentially, thanks to an ample food supply and few predators. By 1855, they had overshot the land’s carrying capacity. Their numbers then stabilized and fluctuated around a carrying capacity of about 1.6 million sheep.
Fig. 5-15, p. 115

38. Science Focus: threat on California’s southern sea otter
Low reproductive rates
Sexual maturity between 2-5 years old
1 pup per yea
Threats
Predation from Orcas
Parasites from cat litter
Thorny-headed worms from seagulls
Toxic algal blooms
Biomagnification from PCB’s
Oil Spills
They serve as indicator species
why?

39. Population Size of Southern Sea Otters Off the Coast of So
Population Size of Southern Sea Otters Off the Coast of So. California (U.S.)
Figure 5.B: This graph tracks the population size of southern sea otters off the coast of the U.S. state of California, 1983–2009. According to the U.S. Geological Survey, the California southern sea otter population would have to reach at least 3,090 animals for 3 years in a row before it could be considered for removal from the endangered species list. (Data from U.S. Geological Survey)
Fig. 5-B, p. 114

40. Case study: white tailed deer populations
White Tailed Deer were greatly threatened in the early 1900’s
Due to habitat destruction and hunting
Laws were passed in 1920’s-30’s to protect remaining deer
Methods used included
Restricted hunting
Elimination of predators
Protection methods worked too well
Population boom

41. Case study: white tailed deer
Problems with deer population explosion
Deer are exploiting suburban areas (feeding on suburbanite’s gardens and farmer’s land)
Spreading Lyme disease to humans (via ticks)
Increased vehicular accidents, human fatalities
Control methods:
Hunting re-opened
Spray predator-scented sprays as a scare tactic
Trapped and moved
Birth control darts

42. Population crash after exceeding carrying capacity
Some populations temporarily exceed the (K) known as OVERSHOOT
A drastic crash may occur if there is a reproductive time lag
Period needed for the birth rate to fall and for the death rate to rise in response to over consumption
This is known as a population
Crash, or dieback

43. Carrying capacity is not fixed
Factors may increase or decrease (k)
Seasonality
Presence/absence of predators
Abundance/scarcity of competitors
Habitat degradation

44. Species have different reproductive rates
Some species reproduce many, small offspring
Do not need to provide significant parental care
 Why not?
Many offspring = greater chances of survival
The number of pre-reproductive deaths will most likely always remain less than the total offspring produced
Conserves time/energy for parent offspring
Some species reproduce later in life and have few offspring
Mature slowly
Require parental care
Which are most susceptible to extinction? Why?

45. Survivorship Curves
I. Humans and other large mammals; those who fit this curve produce few offspring, but provide them with good care II. Ground squirrels, rodents, invertebrates, lizards, annual plants; this curve includes animals with a constant death rate III. Oysters; those within this survivorship curve produce many offspring, but provide little to no care for them

46. Reproductive Strategies (R & K)
R - Unstable environment, density independent
K - Stable environment, density dependent interactions
small size of organism
large size of organism
energy used to make each individual is low
energy used to make each individual is high
many offspring are produced
few offspring are produced
early maturity
late maturity, often after a prolonged period of parental care
short life expectancy
long life expectancy
each individual reproduces only once
individuals can reproduce more than once in their lifetime
type III survivorship pattern  in which most of the individuals die within a short time  but a few live much longer
type I or II survivorship pattern in which most individuals live to near the maximum life span

47. Reproductive Patterns
r-selected species tend to be opportunists while K-selected species tend to be competitors.
Figure 8-10

48. R-selected vs. K-selected

49. Population Density
Population Density: number of individuals in a population found in a particular area or volume

50. Density-Dependent vs Density Independent factors
Density Dependent factors
Have a greater effect as a population increases in density
Examples: infectious disease, competition, space, predation, parasitism
Musical Chairs!
Density-Independent Factors
Does not matter how dense a population is
Examples: seasonal change, catastrophic event, habitat destruction
Think of a population of plants that experience a winter freeze does not matter if there are 50 members in the population or 100 members. The freeze will affect the entire area

51. 4 Different Types of Population Change Occur in Nature
Stable- population size slightly fluctuates above and below (k)
Ex. Species in undisturbed tropical rainforests
Irruptive
Population surge, followed by crash
Common of short-lived rapidly reproducing organisms
Cyclic fluctuations, boom-and-bust cycles
Top-down population regulation
Bottom-up population regulation
Irregular- no particular pattern

52. Population Cycles for the Snowshoe Hare and Canada Lynx
Figure 5.18: This graph represents the population cycles for the snowshoe hare and the Canadian lynx. At one time, scientists believed these curves provided evidence that these predator and prey populations regulated one another. More recent research suggests that the periodic swings in the hare population are caused by a combination of top-down population control—through predation by lynx and other predators—and bottom-up population control, in which changes in the availability of the food supply for hares help to determine their population size, which in turn helps to determine the lynx population size. (Data from D. A. MacLulich)
Cyclic fluctuation patterns
Fig. 5-18, p. 118

53. Estimating Population Sizes
Scientists need to consider several limitations when attempting to estimate population sizes
Mobility/immobility
Distribution patterns
Migration rates
Some methods scientist use to estimate ecological populations:
Random Sampling (best for stationary organisms)
Normally use quadrats
Mark Recapture

54. Mark Recapture P=(M*C)/R P= estimated population size
M=# of 1st Sample that were marked
C= Total number caught in 2nd sample
R= # recaptured (marked) found in sample 2

55. Mark recapture Example
A biologist caught 16 cichlid species from a lake and tagged all of them. He released them back into the lake. A week later, he went back and caught 13 cichlid fish in the same lake and found that 4 of them were tagged individuals he had recaptured. The estimated population of cichlids in the lake would be:
M=16
C=13
R=4
P= (16*13)/4= 52
This method helps with estimating mobile species population sizes

56. Random Sampling Example
Since the area is 4x4, take 4 samples
Find the average number of individuals per square
Multiply is times total number of area (16)
Total Sampled = 29
Average/sample = 7.25
Est. Population = 7.25*16 = 116 10 8 4 7
This method is best for evenly dispersed, stationary populations… why?

57. Humans Are Not Exempt from Nature’s Population Controls
Ireland
Potato crop in 1845
Bubonic plague
Fourteenth century
AIDS
Global epidemic

58. 5-3 How Do Communities and Ecosystems Respond to Changing Environmental Conditions?
Concept 5-3 The structure and species composition of communities and ecosystems change in response to changing environmental conditions through a process called ecological succession.

59. Communities and Ecosystems Change over Time: Ecological Succession
The normally gradual change in species composition in a given area after the area has been disturbed o destroyed in some way
Response to such instances as
Fire
Volcanic eruption
Climate change
Clearing of forests
2 types:
Primary succession
Secondary succession

60. Some Ecosystems Start from Scratch: Primary Succession
Establishment of biotic community in a lifeless area
No soil in a terrestrial system
No bottom sediment in an aquatic system
Takes hundreds to thousands of years
Need to build up soils/sediments to provide necessary nutrients
Pioneer species: first species to inhabit the area
Examples: Moss, Lichens
Occurs after such instances as
Volcanic eruption
Retreating glaciers
Abandoned highway/parking lot
Newly created or shallowed pond/reservoir

61. Primary Ecological Succession
Figure 5.19: Primary ecological succession: Over almost a thousand years, these plant communities developed, starting on bare rock exposed by a retreating glacier on Isle Royal, Michigan (USA) in northern Lake Superior. The details of this process vary from one site to another. Question: What are two ways in which lichens, mosses, and plants might get started growing on bare rock?
Fig. 5-19, p. 119

62. Some Ecosystems Do Not Have to Start from Scratch: Secondary Succession
Some soil remains in a terrestrial system
Some bottom sediment remains in an aquatic system
Much more common than primary succession
Restoration is also much faster than in primary succession
Occurs after disturbances such as
Abandoned farmland
Burned/cut forests
Heavily polluted streams
Flooded land

63. Natural Ecological Restoration of Disturbed Land
Figure 5.20: Natural ecological restoration of disturbed land: This diagram shows the undisturbed secondary ecological succession of plant communities on an abandoned farm field in the U.S. state of North Carolina. It took 150–200 years after the farmland was abandoned for the area to become covered with a mature oak and hickory forest. A new disturbance such as deforestation or fire would create conditions favoring pioneer species such as annual weeds. In the absence of new disturbances, secondary succession would recur over time, but not necessarily in the same sequence shown here. See an animation based on this figure at CengageNOW. Questions: Do you think the annual weeds (left) would continue to thrive in the mature forest (right)? Why or why not?
Fig. 5-20, p. 120

64. Secondary Ecological Succession in Yellowstone Following the 1998 Fire
Figure 5.21: These young lodgepole pines growing around standing dead trees after a 1998 forest fire in Yellowstone National Park are an example of secondary ecological succession.
Fig. 5-21, p. 120

65. Ecological succession Succession
Primary and secondary succession
Tend to increase biodiversity
Increase species richness and interactions among species
Important natural service
Both (primary and secondary) are examples of ecological restoration
Primary and secondary succession can be interrupted by
Fires
Hurricanes
Clear-cutting of forests
Plowing of grasslands
Invasion by nonnative species

66. Science Focus: How Do Species Replace One Another in Ecological Succession?
Facilitation-
One set of species makes an area more suitable for other species and less suitable for itself
Inhibition-
Early species hinder the establishment of other species growth
Succession can proceed when these species are removed
Tolerance-
Plants in the late stages of succession are unaffected/no direct competition with earlier species

67. Succession Doesn’t Follow a Predictable Path
Traditional view- Equilibrium
Balance of nature and a climax community
Climax community: dominated by few long-lived plant species and is in balance with its environment
Current view
Ever-changing mosaic of patches of vegetation
Reflects on-going struggle by species
Mature late-successional ecosystems
State of continual disturbance and change

68. Living Systems Are Sustained through Constant Change
Stability is achieved through change
Environment is constantly changing, thus to keep it stable, living systems must parallel the change by change
2 aspects of stability:
1. Inertia (persistence)
Ability of a living system to survive moderate disturbances
2. Resilience
Ability of a living system to be restored through secondary succession after a moderate disturbance
Some systems have one property, but not the other

69. Some ecosystems have one or the other: resilience or Inertia
Ranforests (example)
High Inertia
High resistance to change due to species diversity and richness
Once severely damaged, have low resilience
Reaches ecological tipping point
Grasslands (example)
High Resilience
Low species diversity makes them susceptible to destruction
Because most plant matter stored in underground roots, they may recover quickly via secondary succession

70. Three Big Ideas
Certain interactions among species affect their use of resources and their population sizes.
There are always limits to population growth in nature.
Changes in environmental conditions cause communities and ecosystems to gradually alter their species composition and population sizes (ecological succession).