Today is Thursday, October 2 nd , 2014

1. In This Lesson: Population Ecology (Lesson 2 of 3) Today is Thursday,October 2nd, 2014 Pre-Class: What’s the smallest biological unit in which evolution can be detected?

2. Today’s Agenda • Large scale biological interactions. • Also known as “locking evolution, physiology, and behavior together in a room and watching what happens.” • Where is this in my book? • Chapters 52-53, but mostly 53.

3. By the end of the lesson… • You should be able to identify the parameters by which a population is measured. • You should be able to describe limits to a population’s growth. • You should be able to solve mathematical problems involving population growth and density.

4. Populations: “What” • So what’s a population? • It’s a group of individuals of the same species in the same place at the same time. • Finding the “boundaries” of the population is based on whether the individuals… • draw on the same resources. • Interact. • interbreed.

5. Populations: “Why” • Like a good experiment, studying entire populations automatically provides a high sample size and therefore can lead to meaningful understanding of what’s happening. • Practically, this can also allow for population management: • Increasing populations (endangered species) • Decreasing populations (pests, invasive species) • Maintaining populations (global marine ecosystems)

6. Populations: “Factors” • Complete analysis of a population requires studying the abiotic factors… • Climate • Sunlight and photoperiod • Soil and nutrients • …as well as the biotic factors… • Competition • Prey/predator populations • Disease • …and the intrinsic factors… • Genetics and evolution

7. Populations: “Descriptions” • Populations are usually described through the following characteristics: • Range • Density • Size • Range, to start, is how far a population spreads and is limited by both abiotic and biotic factors: • Temperature, food availability, predators, humans, New Jersey, et cetera.

8. Population Range Case in Point • Polar bears are migrating further south and are interbreeding with grizzlies (!). • Why? Because rising temperatures and ice surface area (abiotic factors) are forcing them to seek out prey (biotic factor) and land further south.

9. Population Range Case in Point • Case in point deux: Golden Lion Tamarins • They are highly endangered largely because their natural range is small. • Human encroachment is shrinking it further. http://ih2.redbubble.net/image.9367479.1727/flat,550x550,075,f.jpg http://pin.primate.wisc.edu/fs/sheets/maps/leontopithecus_rosalia_range_large.gif

10. Population Spacing • Are there packs? Are they loners? Do all the males need a certain amount of territory? • Importantly, with the answers to those questions in mind, how do we deal with habitat fragmentation. http://www.eoi.es/blogs/mariagutierrez/files/2014/01/bridge.png

11. Population Spacing Clumped dispersion: Uniform dispersion: Random dispersion:

12. Population Dispersion(same as “spacing”) • Clumped is the most common in nature because it indicates “oases” of resources or social behaviors. • Uniform spacing, by the way, is usually distinguished from random or clumped by the presence of territoriality (or maybe something like trees that block out too much sun…which is basically territoriality). • Random is, well, random. Nobody’s territorial or overly social either. • Macaroni Penguins video! What kind of dispersion do they exhibit? • Note to students: That bit about the first egg being bad, but possibly an insurance egg? Remember that. It’s coming back later…

13. Population Size • The size of a population is pretty easy to define. More important is how it changes. • Population size is determined/will change based on: • Sex Ratio (males vs. females) • Generation Time (when is sexual maturity) • Age Structure

14. Generation Time Case in Point • Chilean Sea Bass (Patagonian Toothfish) • If you see this on the menu, don’t order it! • Why? • They live to 50 years old, but they don’t reach sexual maturity until around 20 years old. • As Nature News said, fishing for them is “almost like logging for trees.” • Not a sustainable population! http://graphics8.nytimes.com/images/2006/11/08/dining/08bass.600.jpg

15. Population Size • All those factors (generation time, male/female ratio, et cetera) are considered part of a population’s demography. • Take a look at the life table below:

16. Demography: Survivorship Curve • Take that life table from the previous slide and turn it into a graph. What do you get?

17. Demography: Survivorship Curve • Generally, three different patterns may emerge from a life curve: • High death rate but after reproduction age. • Constant mortality rate. • High initial death rate with longevity for survivors. 1000 Human (type I) Hydra (type II) 100 Survival per thousand Oyster (type III) 10 1 0 25 50 75 100 Percent of maximum life span

18. Demography: Age Structure • You’ve heard the term “baby boomer,” right? • Terms like that describe a cohort of, in this case, people. • What can you learn about the growth rates of these countries using the graphs?

19. Demography: Age Structure • Kenya shows the birth rate is higher than the death rate. • The U.S. shows a slight increase in birth over death. • Italy has a birth rate equal to its death rate. • Key note: These graphs show the youngest cohort at the bottom.

20. So what’s it all mean? • Here’s the big idea, both for population ecology and for biology as a whole: • Life is a trade-off between costs and benefits. • I’m going to say that again for emphasis. • Life is a trade-off between costs and benefits. • You know what? Here’s one more. • Life is a trade-off between costs and benefits.

21. Trade-Offs • How many kids do you (think you) want? • Why? • Whether we think consciously about it or not, there’s always a trade-off in reproduction. • From an evolutionary perspective, reproduction is the ultimate goal, but exactly how many offspring you churn out (especially at one time) can be…interesting.

22. Costs/Benefits of Reproduction • Benefits: • Reproduction. Duh. • Costs: • Reproduction involves a lot of investment in energy, resources, and behavior changes. • Doing so may also lead to increased vulnerability to predation or other risks. • If it weren’t for reproduction, species wouldn’t reproduce.

23. Case in Point: European Kestrels • Researchers artificially increased brood (nest) size in European kestrels, then measured how many birds survived the next winter. • The results?

24. Life Histories • Looking at these various traits – reproductive strategies, timing of reproduction, survivorship…these are all part of an organism’s life history. • Think of life history like “demography,” except something evident in an individual and not just over a population. • Of course, the most obvious element of life history is how an organism reproduces. • Do they tend to have just one or two babies? • Do they tend to “go big or go home?”

25. Reproductive Strategies • Two main reproductive strategies: • r Selection • Reproduce early in life, have lots o’ babies, invest little time in caring for offspring as a parent. • Think insects, many plants, Finding Nemosorta… • K Selection • Have relatively few offspring later in life, invest a lot of parental care. • Primates, elephants, coconuts.

26. Implications of r and K Selection • r selected • Environment is unstable • Density does not adversely affect interactions • Organisms are small • Relatively low energy needed to reproduce • Sexual maturity reached soon • Many offspring • Individuals reproduce only once • Type III survivorship curve • K selected • Environment is stable • Density does affect interactions • Organisms are large • High parental investment in offspring • Sexual maturity reached late • Few offspring • Individuals reproduce multiple times • Type I or II survivorship curve http://www.bio.miami.edu/tom/courses/bil160/bil160goods/16_rKselection.html

27. r and K Selection • Where did these variables come from? • They come from the logistic growth equation. • Population growth rate approaches zero as the population size nears the maximum that can be supported. • r represents the growth rate of a population. • So r selected populations have high growth rates. • K represents the limit of population density. • So K selected populations exist near the density limit.

28. Aside: Within-Species Patterns • Here’s something weird: • In biology, there is certainty of maternity (it’s easy to tell who the mother of a child is), but even if you witness a birth, there is uncertainty of paternity. • Males, therefore, across the animal kingdom are never fully sure they’re the father, and therefore they’re never fully sure they’ll be caring for their genes as they are passed on.

29. Aside: Within-Species Patterns • Therefore, most males, as we know, tend to invest less in their offspring than females do. • The interesting part? • This applies even on a cellular level! • Males churn out a TON of sperm that have relatively small cell volumes and basically just carry DNA. • Females make fewer, relatively LARGE eggs that contain nutrients and protective structures in addition to the DNA.

30. Back to Population Size • The growth of a population also takes a predictable pattern, at least under idea (read: fictional) conditions: More on these in a little bit…

31. Population Growth • That’s an exponential curve, of course, but it represents ideal conditions that lack limiting factors. • These have been achieved a few times, mainly for endangered species: Whooping Cranes (back from extinction) African Elephants (banned hunting)

32. And those limiting factors are…? • As you might guess: • Density-Dependent: • Competition (food, mates, nest sites, et cetera). • Hint hint: Macaroni Penguins! • Disease • Predation • Waste • Density-Independent: • Sunlight, temperature, rainfall.

33. Growth Equations • You may have noticed what looked a little like…calculus?...on those graphs. • Stuff like dN/dt = 1.0N. • These are equations that can help us discuss population growth…quantitatively. • You can expect some of these problems on the AP Test as well as mine. • Let’s explore the types of questions you may be asked.

34. But first! • You do need to remember two things: • r is the growth rate. • So r is positive for growing populations and negative for shrinking populations. • K is the carrying capacity. • The formulas on the next few slides are given to you for the AP Exam and for my tests too, however, not all variables are identified on the formula sheet. • I’ll name them all here so you can learn them.

35. The Variables • dN/dt = change in population size over time. • This is an actual number, not a percentage. • N = population size. • b = per capita birth rate. [per individual] • B = births. • So B/N = b. • d = per capita death rate. [per individual] • D = deaths. • So D/N = d. • r = per capita growth rate [sometimes shown as rmax]. • So r = b – d. • BUT! r ≠ B – D.

36. The Equations (1 of 2) • Population Growth • That’s births minus deaths. • Exponential Growth • That’s the growth rate times population size.

37. The Equations (2 of 2) • Logistic Growth • That’s growth rate times population size, adjusted for how close the population is to carrying capacity. • Population Density • Measured as ___ per ___.

38. Population Growth Rate Example In a population of 312 Andean condors, 17 die over the course of the year while 22 are born. What is the growth rate of the population? The birth rate (B) is 22/312 = 0.071; the death rate (D) is 17/312 = 0.054. 0.017 tells us the population is slightly growing.

39. Exponential Growth Example A population of 43 mice exists in a predator-free field. Each individual mouse has an average litter size of 5 pups each month. How many mice will there be next month? There’s no death rate here, so we’re expecting a large number as an answer. This is an r selected population.

40. Logistic Growth Example An African elephant wildlife refuge has a carrying capacity of 511 elephants. The population is currently at 443 elephants. Assuming a growth rate of 0.009 elephants/year, what will be the change in population size this year? This is a K selected population.

41. Population Density Example • If there are 500 chameleons living in a 3 mi2 area, what’s the density? • 166.67 chameleons/sq. mi.

42. Key Notes • dN/dt is not itself a mini-formula. Think of it as one variable. • It represents the change in a population over a time period, and frequently is either a whole number (like 17) or a rate (like 0.03). • Think of r as the “rate” of growth, and dN/dt as the “amount” of growth. • R is typically, but not always, a decimal. • dN/dt is expressed in terms of “individuals.” • Round any answer that lists an amount of individuals. • So it’s 134 turkeys, not 133.5 turkeys. • Don’t round anything that’s population density.

43. Putting them together… • Let’s try these on our own: • Population Growth Problems 1 • The formula reference section at the top is identical to what you’ll have on the test/AP Exam. • This is the harder worksheet. • Population Growth Problems 2 • This is the easier worksheet.

44. The (Introduced) Elephant in the Room • One of the hottest topics of population ecology is the effect of introduced species on a population. • If the introduced species doesn’t really survive…no big deal. • If it does, however, it may become an invasive species capable of dramatic ecological imbalance. • Invasive species get their name because they tend to explode in number once they find a new niche to occupy in a different habitate.

45. Invasive Species Examples • Brown Tree Snake • Introduced to Guam around WWII. • Nearly eliminated native Micronesian Kingfisher population (yay Philadelphia Zoo!). http://upload.wikimedia.org/wikipedia/commons/e/e2/Micronesian_Kingfisher_1644.jpg http://photos.the-scientist.com/legacyArticleImages/2012/05/05_12_Notebook_snake01.jpg

46. Invasive Species Examples • Zebra Mussel • Native to East Europe/West Russia. • The only freshwater mussel that can attach to objects. • Can attach to and kill native mussels, destroy equipment, and eliminate larval fish food supplies. http://www.fws.gov/midwest/mussel/images/zebra_mussels_on_native2_620.jpg http://3.bp.blogspot.com/-96Yfb0lrtFI/ToXwLf557wI/AAAAAAAAACM/Q7El411zveM/s400/zebra_mussel_shopping_cart.gif

47. Invasive Species Examples • European Starling • Introduced to Central Park, NYC, by a woman who wanted the park to have all the animals mentioned in Shakespeare’s plays. • Not particularly harmful other than providing an unnecessary level of competition. • Despised by lots of birders, nevertheless. http://www.allaboutbirds.org/guide/PHOTO/LARGE/european_starling_16.jpg

48. Invasive Species Effects • Broadly: • Exponential growth of introduced species. • Lack of predators or adequate competition. • Overall decline in biodiversity. • Eradication of native species. • Sound familiar? • Humans are invasive species!

49. Back to Population Growth • In the absence of predators, competition, and other limiting factors, we know we’ll see exponential growth. • In reality, populations reach a point at which their environment and resources can no longer sustain further expansion. • Not to mention the predator population may start to become overwhelming. • This point is called the carrying capacity of a population, and it’s geo-specific (depends on the environment). • At carrying capacity, population growth can still fluctuate but generally has little net change. • One more thing: Carrying capacity is given, confusingly, by the letter K.

50. Population Growth Without Limiting Factors With Limiting Factors