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Chapter 9 Population Dynamics, Carrying Capacity, and Conservation Biology.

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1 Chapter 9 Population Dynamics, Carrying Capacity, and Conservation Biology

2 Key Questions How do populations change in size, density, and makeup? What is the role of predators in controlling population size? What is conservation biology? How can we live more sustainably? How do populations change in size, density, and makeup? What is the role of predators in controlling population size? What is conservation biology? How can we live more sustainably?

3 Major Characteristics of a Population Populations can change in… 1.Size (number of individuals) 2.Density (number of individuals in a certain area) 3.Dispersion (spatial pattern) 4.Age distribution Populations can change in… 1.Size (number of individuals) 2.Density (number of individuals in a certain area) 3.Dispersion (spatial pattern) 4.Age distribution

4 Clumped (elephants) Uniform (creosote bush) Random (dandelions) Dispersion

5 These changes are called… Population Dynamics! -occur in response to environmental stress OR changes in environmental conditions Population Dynamics! -occur in response to environmental stress OR changes in environmental conditions

6 What Limits Population Growth? Births Deaths Immigration (to a new area) Emigration (out of an area) Population change = (births + immigration) – (deaths + emigration) Births Deaths Immigration (to a new area) Emigration (out of an area) Population change = (births + immigration) – (deaths + emigration)

7 Populations Populations vary in biotic potential (growth) Intrinsic rate of increase (r)-rate at which a population would grow if it had unlimited resources Populations vary in biotic potential (growth) Intrinsic rate of increase (r)-rate at which a population would grow if it had unlimited resources

8 High intrinsic rate of increase populations… Reproduce early in life Short generation times Reproduce many times Many offspring each time they reproduce Reproduce early in life Short generation times Reproduce many times Many offspring each time they reproduce

9 Example… FLIES!-high intrinsic rate of increase/biotic potential Without control, there would be 5.6 trillion flies within 13 months Within a few years, flies could cover the surface of the earth! FLIES!-high intrinsic rate of increase/biotic potential Without control, there would be 5.6 trillion flies within 13 months Within a few years, flies could cover the surface of the earth!

10 Of course… This is not realistic because no population can grow indefinitely There are always limiting factors! This is not realistic because no population can grow indefinitely There are always limiting factors!

11 Environmental Resistance all limiting factors together the biotic potential and environmental resistance determine the carrying capacity all limiting factors together the biotic potential and environmental resistance determine the carrying capacity

12 POPULATION SIZE Growth factors (biotic potential) Favorable light Favorable temperature Favorable chemical environment (optimal level of critical nutrients) Abiotic Biotic High reproductive rate Generalized niche Adequate food supply Suitable habitat Ability to compete for resources Ability to hide from or defend against predators Ability to resist diseases and parasites Ability to migrate and live in other habitats Ability to adapt to environmental change Decrease factors (environmental resistance) Too much or too little light Temperature too high or too low Unfavorable chemical environment (too much or too little of critical nutrients) Abiotic Biotic Low reproductive rate Specialized niche Inadequate food supply Unsuitable or destroyed habitat Too many competitors Insufficient ability to hide from or defend against predators Inability to resist diseases and parasites Inability to migrate and live in other habitats Inability to adapt to environmental change Population Size © 2004 Brooks/Cole – Thomson Learning

13 A Few More Terms Carrying Capacity (K)-number of individuals that can be sustained in a given space Minimum viable population (MVP)- minimum population size needed to support a breeding population (below MVP, extinction is likely) Carrying Capacity (K)-number of individuals that can be sustained in a given space Minimum viable population (MVP)- minimum population size needed to support a breeding population (below MVP, extinction is likely)

14 Exponential and Logistic Growth A population has exponential growth when it has few/no resource limitations (J-shaped curve) Logistic growth- exponential population growth that approaches carrying capacity and levels off (S-shaped curve) A population has exponential growth when it has few/no resource limitations (J-shaped curve) Logistic growth- exponential population growth that approaches carrying capacity and levels off (S-shaped curve)

15 © 2004 Brooks/Cole – Thomson Learning Time (t) Population size (N) K Exponential Growth Logistic Growth

16 What Happens If Population Size Exceeds Carrying Capacity? Overshoot-exceeds carrying capacity Dieback-happens unless individuals change resources or move to another area Humans are not exempt from this! Potato fungus in Ireland; 1 million died/3 million emigrated Overshoot-exceeds carrying capacity Dieback-happens unless individuals change resources or move to another area Humans are not exempt from this! Potato fungus in Ireland; 1 million died/3 million emigrated

17 2.0 1.5 1.0.5 Number of sheep (millions) 180018251850187519001925 Year Overshoot

18 How Does Density Affect Population Growth? Density-independent population controls (do NOT depend on size of population): floods, fires, hurricanes, habitat destruction, pesticides Density-dependent population controls (depend on size of population): competition, predation, disease, parasitism Density-independent population controls (do NOT depend on size of population): floods, fires, hurricanes, habitat destruction, pesticides Density-dependent population controls (depend on size of population): competition, predation, disease, parasitism

19 Population Curves in Nature Stable: fluctuates slightly above and below carrying capacity (undisturbed areas) Irruptive: fairly stable with occasional explosions Irregular: chaotic, no recurring pattern Cyclic: regular cycles Stable: fluctuates slightly above and below carrying capacity (undisturbed areas) Irruptive: fairly stable with occasional explosions Irregular: chaotic, no recurring pattern Cyclic: regular cycles

20 Natural Population Curves

21 Do Predators Control Population Size? YES! Lynx-Hare Cycle: Shortage of hares reduces lynx population Hare population builds up because there are fewer predators Lynx population increases because there are more hares Cycle begins again YES! Lynx-Hare Cycle: Shortage of hares reduces lynx population Hare population builds up because there are fewer predators Lynx population increases because there are more hares Cycle begins again

22 Two Ideas About Lynx-Hare Cycle Top-down control hypothesis: lynx controls hare population Bottom-up control hypothesis: hare controls lynx population Top-down control hypothesis: lynx controls hare population Bottom-up control hypothesis: hare controls lynx population

23 Population size (thousands ) 160 140 120 100 80 60 40 20 0 Year Hare Lynx

24 Reproductive Patterns and Survival Asexual reproduction: all offspring are exact copies (clones) of a single parent Sexual reproduction: combination of gametes (97% of species) r-selected species K-selected species Asexual reproduction: all offspring are exact copies (clones) of a single parent Sexual reproduction: combination of gametes (97% of species) r-selected species K-selected species

25 Reproductive Patterns r-selected: opportunist species; high intrinsic rate of increase; reproduce early; algae, bacteria, rodents, insects Many offspring each time they reproduce Reproduce at young age Short generation times Little or no parental care Short life-spans Irregular and unstable changes in population size r-selected: opportunist species; high intrinsic rate of increase; reproduce early; algae, bacteria, rodents, insects Many offspring each time they reproduce Reproduce at young age Short generation times Little or no parental care Short life-spans Irregular and unstable changes in population size

26 r-Selected Species cockroachdandelion 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

27 Reproductive Patterns, continued K-selected: competitor species; mammals, long-lived plants, birds of prey Reproduce late in life Few offspring Long generation times Nurture and protect their young Logistic growth curve K-selected: competitor species; mammals, long-lived plants, birds of prey Reproduce late in life Few offspring Long generation times Nurture and protect their young Logistic growth curve

28 Fewer, larger offspring High parental care and protection of offspring Later reproductive age 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 elephantsaguaro K-Selected Species

29 Figure 9-9 Page 196 Number of individuals Time Carrying capacity K species; experience K selection r species; experience r selection K

30 Survivorship Curves Shows the number of survivors of each age group for a species 3 Types: 1. Late Loss Curves: high survivorship to a certain age, then high death rate (elephants, humans) 2. Constant Loss Curves: constant death rate at all ages (songbirds) 3. Early Loss Curves: survivorship is low early in life (r-selected species) Shows the number of survivors of each age group for a species 3 Types: 1. Late Loss Curves: high survivorship to a certain age, then high death rate (elephants, humans) 2. Constant Loss Curves: constant death rate at all ages (songbirds) 3. Early Loss Curves: survivorship is low early in life (r-selected species)

31 Percentage surviving (log scale) 100 10 1 0 Age

32 Conservation Biology Started in the 1970s Uses science to take action to preserve species and ecosystems 3 principles 1.Biodiversity is necessary to all life on earth and should not be reduced by humans 2.Humans should not disrupt vital ecological processes 3.The best way to preserve earths biodiversity is to protect ecosystems Started in the 1970s Uses science to take action to preserve species and ecosystems 3 principles 1.Biodiversity is necessary to all life on earth and should not be reduced by humans 2.Humans should not disrupt vital ecological processes 3.The best way to preserve earths biodiversity is to protect ecosystems


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