1. Population Dynamics Chapter 8

2. Sea Otter – the other, other white meat Why are sea otters considered keystone species? They control urchin populations which feed on kelp, hence they keep the kelp forests healthy Why did their populations decline? Originally due to hunting, now chemical pollution is suspected

3. Characteristics of a population Size – number of organisms Density – number /space Dispersion – spatial distribution Age distribution – pre-breeding, breeding, or post breeding age Population dynamics – how these factors change due to environmental stresses

4. Population growth Population change (growth) = (births + immigration) – (deaths + emigration) ZPG – zero population growth is when incoming equals outgoing Biotic potential – max growth for that particular population Intrinsic rate of increase – rate of growth with unlimited resources

5. High intrinsic growth rates Reproduce early in life Have short time between generations Reproduce many times Have many offspring each time Roaches, mice, fish, flies

6. Environmental Resistance These are the vast assortment of environmental factors which help keep populations from growing out of control This is a way a population finds an equilibrium point

7. Fig. 9.3, p. 200 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

8. Carrying capacity Biotic potential and environmental resistance will determine the population a given area can hold and sustain indefinitely A population must not drop below the minimum viable population or lowest number needed to keep population from disappearing due to environmental resistance

9. Fig. 9.5, p. 201 2.0 1.5 1.0.5 Number of sheep (millions) 180018251850187519001925 Year

10. Logistic growth Exponential growth (J curve) is not possible forever because resources and space eventually run out. When a population reaches a certain point, environmental resistance increases causing the population size to stabilize. This is known as logistic growth (s curve) and this generally happens to all populations

11. Fig. 9.4, p. 201 Time (t) Population size (N) K Exponential GrowthLogistic Growth

12. Can you overshoot your carrying capacity? Absolutely, it happens all the time When you have too many individuals for the area to support you will have a population crash If the overshoot was not too drastic, and the crash was small the population re-stabilizes

13. Types of population curves Stable – nearly flat line Irregular – widely fluctuating pattern with no periodicity Cyclic – regular growth and crash at set intervals, usually seasonal Irruptive – normally stable, but with a random spike or crash

14. Fig. 9.7, p. 202 Number of individuals Time Irruptive Stable Cyclic Irregular

15. Top-down or bottom-up? Evidence seem to show both happening Top-down – predators hunt and kill prey keeping their population stable Bottom-up – prey are the food source that allow predators to keep the populations up

16. Types of reproduction Asexual – cloning, single parent donates both parts of DNA (bacteria) Sexual – two parents donate DNA Females have to give birth more (males do not as in asexual) More genetic errors from combining Mating is more damaging, and energy intensive Does provide more genetic diversity, hence a stronger species

17. R-selected species Also known as r-strategists and fill generalist niche Have many offspring Reach reproductive age early Short time between generations Little to no parental care and adapted to unstable climate (low survivorship) Short life span (usually under a year) Algae, rodents, bacteria, annual plants and insects

18. Fig. 9.10a, p. 205 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

19. K-selected species K-strategists or competitors, specialist niche Fewer, larger offspring (usually develop inside) Mature slowly (often protected while vulnerable) Lower population growth rate Long lived with stable population near carrying capacity Depend heavily upon suitable habitat Large mammals, birds of prey, long lived plants such as oaks, redwoods, some cacti

20. Fig. 9.10b, p. 205 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

21. Survivorship curve Late loss - typical for k-strategists Early loss – typical for r-strategists Constant loss – for species in the gray area in- between k and r strategists with intermediate reproductive patterns Song birds, lizards, and small mammals

22. Fig. 9.11, p. 206 Percentage surviving (log scale) 100 10 1 0 Age

23. Conservation biology Sensible use of natural resources Originated in 1970’s – uses current science Investigate human impact on the biodiversity Develop practical approaches to maintain biodiversity Maintain – endangered species, wildlife reserves, ecological restoration, ecological economics, environmental ethics

24. Assumptions of conservation bio Biodiversity is necessary Humans should not affect extinction or vital environmental processes Protecting ecosystems is the best way to protect Based on Aldo Leopold’s ethical principle, that if we maintain the earth’s life-support system it is appropriate

25. Human impact on ecosystems Fragmentation – breaking up large tracts with roads, fences, towns, etc. Habitat loss/degradation – pollution, lumber, mining, etc. Simplifying ecosystems – lower biodiversity through habitat change (monocultures) Strengthening species – pesticide use, antibiotics

26. Human impact continued Predator elimination – wolves, coyotes, bear, etc. Introduce alien species Overharvest potentially renewable resources – trees, soil, other biomass (grasses, nuts, etc) Interfere with natural chemical cycling – clear cutting, monocultures, pesticides (we kill and simplify a system)

27. Way to go humans!! You’re the best! Goals for the future (if we want to be a part of it) Maintain balance between human impacted simple ecosystems and natural rich ecosystems Slow down rates at which we alter nature for our own purpose Realize that we never do merely one thing, everything is interdependent and unpredictable

28. How can you help Use consumer power – buy products that are friendly to the environment Use voting power – elect officials that will strive to protect the environment Educate – most people have no idea about the consequences of their actions Identify “mother culture” that says spend, buy, consume and learn to tune it out Exploit nature for its aesthetics and renewable resources

29. That’s all folks Have a nice day