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Biodiversity, Species Interactions, and Population Control

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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 Hunted: early 1900s Partial recovery Why care about sea otters? Ethics Keystone species Tourism dollars

3 Case Study: Sea Otters Are They Back From the Brink of Extinction
Sea otters a tool-using mammals, uses stones to prey shellfish off rocks underwater and to break open the shells while swimming on the their backs and using their bellies as a table. They consume a ¼th of their weight each day in sea urchins, clams, mussels, crabs, abalones and about 40 other species of bottom-dwelling organisms. . They are the only marine mammal that lacks blubber, they can trap air under their fur for insulation. Early 1900’s almost extinct. They were hunted for fur and because they competed with fishers for valuable abalone declared endangered. Most remaining species are found between California’s coastal cities of Santa Cruz and Los Angeles. (a) Southern sea otter (b) Sea Urchin (c) Kelp bed

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 Most Species Compete with One Another for Certain Resources
Competition the struggle among organisms, both of the same and of different species, for food, space, and other vital requirements. Competitive exclusion principle The principle that when two species compete for the same critical resources within an environment, one of them will eventually outcompete and displace the other. The displaced species may become locally extinct, by either migration or death, or it may adapt to a sufficiently distinct niche within the environment so that it continues to coexist noncompetitively with the displacing species.

6 Species Interact in Five Major Ways
Interspecific Competition Predation Parasitism Mutualism Commensalism

7 Interspecific competition
Competition between two different species For food, sunlight, water, soil, space One species may migrate or shift feeding habits or face extinction Example-native ants and nonnative fire ants Intraspecific competition competition between members of the same species Natural capital: resource partitioning and niche specialization as a result of competition between two species. The top diagram shows the overlapping niches of two competing species. The bottom diagram shows that through evolution the niches of the two species become separated and more specialized (narrower) so that they avoid competing for the same resources.

8 Most Consumer Species Feed on Live Organisms of Other Species
Predators may capture prey by Pursuit Walking Swimming Flying Pursuit and ambush Camouflage Chemical warfare






14 Most Consumer Species Feed on Live Organisms of Other Species
Prey may avoid capture by Camouflage Chemical warfare Warning coloration Mimicry Deceptive looks Deceptive behavior Swift movement Shell

15 Some ways prey species avoid their prey
Span worm Wandering leaf insect Bombardier beetle Foul-tasting monarch butterfly Poison dart frog Viceroy butterfly mimics monarch butterfly When touched, the snake caterpillar changes shape to look like the head of a snake Hind wings of moth resemble eyes of a much larger animal Some ways prey species avoid their prey







22 Parasitism, Mutualism, Commensalism

23 Parasitism Live on or in another species Host is harmed
Ex. Tapeworms, ticks, fleas, mosquitoes, candiru (vampire fish)                      

24 Mutualism (benefits both species)
Pollination mutualism (between flowering plants and animals) Nutritional mutualism Lichens grow on trees Birds/rhinos- nutrition and protection Clownfish/sea anemones Inhabitant mutualism Vast amount of organisms like bacteria in an animal’s digestive tract Termites and bacteria in gut                      

25 . Coral Reefs- The corals get food and the zooxanthellae (algae) get protection. zooxanthellae

26 Yucca and Yucca Moth Yucca’s only pollinator is the yucca moth. Hence entirely dependent on it for dispersal. Yucca moth caterpillar’s only food is yucca seeds. Yucca moth lives in yucca and receives shelter from plant. Example of co evolution

27 Oxpeckers and black rhinoceros Clown fish and sea anemone
Figure 8-10 Page 155 Oxpeckers and black rhinoceros Clown fish and sea anemone Examples of Mutualism Mycorrhizae fungi on juniper seedlings in normal soil Lack of mycorrhizae fungi on juniper seedlings in sterilized soil

28 Commensalism Helps one species but does nothing for the other
                                                                                                                   Commensalism Helps one species but does nothing for the other Ex. Redwood sorrel grows in shade of redwood - Humans and Eyelash Mites

29 Science Focus: Why Should We Care about Kelp Forests?
Kelp forests: biologically diverse marine habitat Major threats to kelp forests Sea urchins Pollution from water run-off Global warming

30 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.

31 Some Species Evolve Ways to Share Resources
Resource partitioning Reduce niche overlap Use shared resources at different Times Places Ways

32 Resource partitioning
Evolve more specialized traits Sharing the wealth: resource partitioning of five common species of insect-eating warblers in the spruce forests of Maine. Each species minimizes competition with the others for food by spending at least half of its feeding time in a distinct portion (shaded area) of the spruce trees, and consuming somewhat different insect species. Five species of common insect-eating warblers in the Spruce forests of Maine

33 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.

34 Characteristics of a Population
Population - individuals inhabiting the same area at the same time Population Dynamics: is the study of how population change due to Population Size - number of individuals Population Density - population size in a certain space at a given time Population Dispersion - spatial pattern in habitat Age distribution - proportion of individuals in each age group in population

35 Populations Have Certain Characteristics
Changes in population characteristics due to: Temperature Presence of disease organisms or harmful chemicals Resource availability Arrival or disappearance of competing species

36 Population Size Natality Mortality
Number of individuals added through reproduction Crude Birth Rate - Births per 1000 Total Fertility Rate – Average number of children born alive per woman in her lifetime Mortality Number of individuals removed through death Crude Death Rate- Deaths per 1000

37 Population Density Population Density (or ecological population density) is the amount of individuals in a population per unit habitat area Some species exist in high densities - Mice Some species exist in low densities - Mountain lions Density depends upon social/population structure mating relationships time of year

38 Population Dispersion
Population dispersion is the spatial pattern of distribution There are three main classifications Clumped: individuals are lumped into groups ex. Flocking birds or herbivore herds due to resources that are clumped or social interactions most common

39 Most Populations Live Together in Clumps or Patches
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 Temporary groups for mating and caring for young

40 Population Dispersion
Uniform: Individuals are regularly spaced in the environment - ex. Creosote bush due to antagonism between individuals, or do to regular spacing of resources rare because resources are rarely evenly spaced tips/2002/clover611.htm Random: Individuals are randomly dispersed in the environment ex. Dandelions due to random distribution of resources in the environment, and neither positive nor negative interaction between individuals rare because these conditions are rarely met Uniform penguins often exhibit uniform spacing by aggressively defending their territory among their neighbors. The leaves of the creosote bush are coated with a resin to prevent water loss in the hot desert. The resin of the creosote bush also protects the plant from being eaten by most mammals and insects. It is believed that the bush produces a toxic substance to keep other nearby plants from growing. Creosote bushes are very long lived, many of them existing for one hundred years, and can grow to a height of 15 feet. Random Tropical fig trees exhibit random distribution as well because of wind pollination. oyster larvae can travel hundreds of kilometers powered by sea currents, which causes random distribution when the larvae land in random places

41 Age Structure The age structure of a population is usually shown graphically The population is usually divided up into prereproductives, reproductives and postreproductives The age structure of a population dictates whether is will grow, shrink, or stay the same size

42 Age Structure Diagrams
Positive Growth Zero Growth Negative Growth (ZPG) Pyramid Shape Vertical Edges Inverted Pyramid

43 Population change= (Birth + Immigration)- (Death + Emigration)
Four variables influencing growth Births Deaths Immigration Emigration Increase  by birth & immigration Decrease  death & emigration Population change= (Birth + Immigration)- (Death + Emigration)

44 No Population Can Grow Indefinitely: J-Curves and S-Curves (1)
Biotic potential - is the population’s capacity for growth Low generally large animals elephant and blue whales High small individuals like bacteria and insects Intrinsic rate of increase (r) is the rate of population growth with unlimited resources.

45 Rapidly growing populations have four characteristics (high r)
Reproduction early in life Short periods between generations Long reproductive lives Multiple offspring each time they reproduce A single house fly could total 5.6 trillion house flies within 13 months

46 No Population Can Grow Indefinitely: J-Curves and S-Curves (2)
Size of populations limited by Light Water Space Nutrients Exposure to too many competitors, predators or infectious diseases

47 Environmental Resistance
Consists of all factors that act to limit the growth of a population Abiotic Contributing Factors: Unfavorable light Unfavorable Temperatures Unfavorable chemical environment - nutrients Biotic Contributing Factors: Low reproductive rate Specialized niche Inability to migrate or disperse Inadequate defense mechanisms Inability to cope with adverse conditions


49 Limits on population growth
Carrying capacity [K] determined by biotic potential & environmental resistance This is the # of a species’ individuals that can be sustained indefinitely in a specific space As a population reaches its carrying capacity, its growth rate will decrease because resources become more scarce.

50 No population can grow forever
No population can grow forever. Exponential growth (lower part of the curve) occurs when resources are not limiting and a population can grow at near its intrinsic rate increase ( r ) or biotic potential. Such exponential growth is converted to logistic growth, in which the growth rate decreases as the population gets larger and faces environmental resistance. With time, the population size stabilizes at or near the carrying capacity ( K )of its environment and results in the sigmoid (s-shaped) population growth curve shown in this figure. Depending on resource availability, the size of a population often fluctuates around its carrying capacity.

51 Population Growth Populations show two types of growth
With few resource limitations Exponential J-shaped curve Growth is independent of population density The growth rate levels off as population reaches carrying capacity Logistic S-shaped curve Growth is not independent of population density


53 Science Focus: Why Are Protected Sea Otters Making a Slow Comeback?
Low biotic potential Prey for orcas Cat parasites Toxic algae blooms PCBs and other toxins Oil spills Sexual years Reproduce until age 15 one pup a year Orcas main prey seals numbers have been declining Cat owners have been flushing cat litter or dump in storm drains enters the coastal waters Algea blooms from bird guano

54 When a Population Exceeds Its Habitat’s Carrying Capacity, Its Population Can Crash
Carrying capacity: not fixed Reproductive time lag may lead to overshoot Dieback (crash) Damage may reduce area’s carrying capacity

55 Population overshoots carrying capacity 2,000 Population crashes 1,500 Number of reindeer 1,000 Carrying capacity When 26 reindeer (24 of them females) were introduced in 1910, lichens, mosses, and other food sources were plentiful. By 1935, the herd population had soared to 2,000 overshooting the islands carrying capacity. This lead to a population crash, with the herd plummeting to only 8 reindeer by 1950. 500 1910 1920 1930 1940 1950 Year Exponential growth, overshoot, and population crash of reindeer introduced to a small island off of SW Alaska

56 Reproductive Strategies
Goal of every species is to produce as many offspring as possible Each individual has a limited amount of energy to put towards life and reproduction This leads to a trade-off of long life or high reproductive rate Natural Selection has lead to two strategies for species: r - strategists and K - strategists

57 r - Strategists Spend most of their time in exponential growth
High rate of reproduction Little parental care Minimum life Opportunist K

58 R Strategists Many small offspring
Little or no parental care and protection of offspring Early reproductive age Most offspring die before reaching reproductive age Small adults Adapted to unstable climate and environmental conditions High population growth rate – (r) Population size fluctuates wildly above and below carrying capacity – (K) Generalist niche Low ability to compete Early successional species

59 K - Strategists Maintain population at carrying capacity (K) K
Maximize lifespan Competitor Follow a logistic growth curve K

60 K- Strategist Reproduce later in life Fewer, larger offspring
High parental care and protection of offspring Most offspring survive to reproductive age Larger adults Adapted to stable climate and environmental conditions Lower population growth rate (r) Population size fairly stable and usually close to carrying capacity (K) Specialist niche High ability to compete Late successional species Prone to extinction

61 Genetic Diversity Can Affect the Size of Small Populations
Founder effect Demographic bottleneck Genetic drift Inbreeding Minimum viable population size- the number of individuals populations need for long term survival

62 Effects of Genetic Variations on Population Size
Genetic diversity 1. Founder effect Few individuals move to a new location and are isolated from the original population Limited genetic diversity

63 2. Demographic bottleneck
Few individuals survive a catastrophe- fire, hurricane Lack of genetic diversity may limit these individuals to rebuild the population

64 3. Genetic drift 4. Inbreeding Random changes in gene frequencies
May help or hurt survival of a population Some individuals may breed more than others and their genes may eventually dominate the gene pool of the population 4. Inbreeding Members of a small population exchange genes

65 Density of a population density
Density-independent (affects population size regardless of its density) Floods, hurricanes, fire, pesticide spraying , pollution) Density-dependent (greater effect as population density increases) Competition for resources, predation, parasitism, disease – bubonic plague)

66 Population fluctuations in nature
Stable (varies slightly above and below carrying capacity,K) Irruptive (explode to a high level and then drastically drop - insects) Cyclic (over a regular time period – lemmings populations rise and fall ever 3-4 years) Irregular behavior (no pattern)

67 General types of simplified population changes curves found in nature
© 2004 Brooks/Cole – Thomson Learning (d) Irregular (a) Stable Number of individuals (c) Cyclic (b) Irruptive Time

68 Population size (thousands)
160 Hare 140 Lynx 120 100 Population size (thousands) 80 60 40 20 For decades, predation has been the explanation for the 10-year population cycle of the snowshoe hare and its predator, the Canadian Lynx. According to this top-down control hypothesis, lynx preying on hares periodically reduced the hare population. The shortage of hares then reduced the lynx population, which allows the hare population to build up again. At some point the lynx population increases to take advantage of the increased supply of hares, starting the cycle again. However, researchers have found that snowshoe hare have a 10 year boom-and-bust cycles on islands where lynx are absent. These scientist hypothesizes that the periodic crashes in the hare population can also be influenced by their food supply. Once the hare populations crash the plants can recover and the hare population begins rising again. If this bottom-up control theory is correct the lynx do not control the hare population. Instead, the changing hare population size may cause fluctuations in the lynx populations. It more than likely a combination of the two factors, predation and food supplies. 1845 1855 1865 1875 1885 1895 1905 1915 1925 1935 Year Predator – prey relationships Lynx-Hare Cycle Cyclic ever 10 years

69 Humans Are Not Exempt from Nature’s Population Controls
Ireland Potato crop in 1845 1 million people died from hunger or disease form malnutrition 3 million migrated to other countries (mainly U.S.) Bubonic plague Fourteenth century Killed a least 25 million people in European Cities AIDS Global epidemic Between AIDS has killed more than 25 million people Claims 2.1 million a year ( average of 4 deaths per min.)

70 Case Study: Exploding White-Tailed Deer Population in the U.S.
1900: deer habitat destruction and uncontrolled hunting 1920s–1930s: laws to protect the deer Current population explosion for deer Lyme disease Deer-vehicle accidents Eating garden plants and shrubs Ways to control the deer population

71 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.

72 Communities and Ecosystems Change over Time: Ecological Succession
Natural ecological restoration Primary succession is ecological succession in a bare area that has never been occupied by a community of organisms. Bare rock exposed by retreating glacier, severe erosion, newly cooled lava, abandoned concrete/ highway, newly created pond Secondary succession is an ecological succession in an area in which natural vegetation has been removed or destroyed but the soil is not destroyed. forest fires, deforestation, abandoned farmland, heavily polluted streams, and land that has been damned or flooded.

73 Succession = change 1. Primary succession
Gradual establishment of biotic community on lifeless ground Barren habitat Bare rock / retreating glacier A newly- cooled lava A newly formed pond It takes several centuries to several thousands of years for natural processes to produce fertile soil. Ex. Hawaii Pioneer species (lichens, moss and microbes)

74 Some Ecosystems Start from Scratch: Primary Succession
No soil in a terrestrial system No bottom sediment in an aquatic system Early successional plant species, pioneer Bacteria, moss, lichens Midsuccessional plant species Herbs and shrubs Late successional plant species Balsam fir, paper birch, and white spruce

75 Primary Succession Glacier Retreat

76 Primary Succession Balsam fir, paper birch, and white spruce
Exposed rocks Lichens and mosses Balsam fir, paper birch, and white spruce climax community Primary succession is ecological succession in a bare area that has never been occupied by a community of organisms. Primary Succession the ground is nearly lifeless; no soil present in a terrestrial ecosystem; no bottom sediment in an aquatic ecosystem Bare rock exposed by retreating glacier, severe erosion, newly cooled lava, abandoned concrete/ highway newly created pond Jack pine, black spruce, and aspen Heath mat Small herbs and shrubs Time

77 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 Ecosystem has been Disturbed Removed Destroyed


79 Mature oak-hickory forest
Secondary Succession Mature oak-hickory forest Secondary succession is an ecological succession in an area in which natural vegetation has been removed or destroyed but the soil is not destroyed. Secondary Succession: a biotic community is already present; soil or bottom sediment is present Examples, forest fires, deforestation, abandoned farmland, heavily polluted streams, and land that has been damned or flooded. Young pine forest Perennial weeds and grasses Shrubs Annual weeds Time

80 Some Ecosystems Do Not Have to Start from Scratch: Secondary Succession (2)
Primary and secondary succession Tend to increase biodiversity Increase species richness and interactions among species Primary and secondary succession can be interrupted by Fires Hurricanes Clear-cutting of forests Plowing of grasslands Invasion by nonnative species

81 Succession of an Aquatic Ecosystem
Aquatic ecosystem gradually increasing in sedimentation/inflow of nutrients from surrounding land areas Slowly filling w/ silt, sand and other particles; shoreline gradually advances toward the center of the pond; Aquatic vegetation contributing to this filling In a “classic scenario” the pond would eventually become a wetland, then perhaps a grassland, followed by some type of forest.


83 Science Focus: How Do Species Replace One Another in Ecological Succession?
1. Facilitation One species makes an area of suitable for another species Ex. Moss build land for grasses 2. Inhibition Early species limit later species Ex. Plants may release toxins 3. Tolerance Later species are unaffected by earlier species

84 Succession Doesn’t Follow a Predictable Path
Traditional view Balance of nature and a climax community Current view Ever-changing mosaic of patches of vegetation Mature late-successional ecosystems State of continual disturbance and change

85 Living Systems Are Sustained through Constant Change
Inertia, persistence Ability of a living system to survive moderate disturbances Resilience Ability of a living system to be restored through secondary succession after a moderate disturbance Tipping point Where any additional stress can cause the system to change in an abrupt and usually irreversible way

86 The Cats of Borneo What happened first? Arrange the sentence strips in chronological order

87 Operation Cat Drop One of the most bizarre events to accompany this early use of DDT occurred when it became necessary to parachute cats into remote jungle villages in what was then Burma.  The following account was taken from a source at Cornell University: In the early 1950s, the Dayak people in Borneo suffered from malaria. The World Health Organization had a solution: they sprayed large amounts of DDT to kill the mosquitoes which carried the malaria. The mosquitoes died, the malaria declined; so far, so good. But there were side-effects. Among the first was that the roofs of people's houses began to fall down on their heads. It seemed that the DDT was also killing a parasitic wasp which had previously controlled thatch-eating caterpillars. Worse, the DDT-poisoned insects were eaten by geckoes, which were eaten by cats. The cats started to die, the rats flourished, and the people were threatened by outbreaks of sylvatic plague and typhus. To cope with these problems, which it had itself created, the World Health Organization was obliged to parachute14,000 live cats into Borneo.

88 The Day they Parachuted Cats into Borneo
WHO sent DDT to Borneo. Mosquitoes were wiped out. Caterpillar numbers went up. Caterpillars ate grass roofs. Roaches stored DDT in their bodies. Lizards ate roaches and got DDT. Lizards slowed down. Cats caught lizards containing DDT. Lizards disappeared. Cats died. Rats increased. Rats brought the plague. Cats were parachuted in.

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