Population Ecology Definition of Population Group of individuals

Population Ecology

Definition of Population: • Group of individuals of a single species living in a specific geographic region at the same time

Study of populations in relation to environment – Environmental influences on: • population density • age structure • population distribution (dispersion)

• Density is the result of a dynamic interaction of processes that add individuals to a population and those that remove individuals from it Births and immigration add individuals to a population. Births Immigration How do these factors Contribute to Population Size? ? Popu. Iation size • Births • Deaths • Immigration • Emigration Deaths and emigration remove individuals from a population.

Clumped Dispersion – Individuals aggregate in patches – May be influenced by resource availability and behavior

Uniform Dispersion – – Individuals are evenly distributed May be influenced by social interactions such as territoriality

Random Dispersion • Position of each individual is independent of other individuals (c) Random. Dandelions grow from windblown seeds that land at random and later germinate.

How do wildlife biologists quantify populations? Defined Populations -complete counts -indirect counts Undefined Populations Mark and Recapture

Life history traits are products of natural selection • Life history traits are evolutionary outcomes – Reflected in the development, physiology, and behavior of an organism • Three things needed quantify life history i. When reproduction begins ii. How often organism reproduces iii. How many offspring produced

Semelparity: Big Bang – Reproduce a single time and die – putting all available resources into maximizing reproduction at the expense of future life

Iteroparity – Repeated Reproduction – – produce offspring repeatedly over time increased parental care along with enhanced energetic investment per offspring

“Trade-offs” and Life Histories • Organisms have finite resources – Kestrels: • Produce a few eggs? – • Can invest more into each, ensuring greater survival Produce many eggs? – Costly but if all survive, fitness is better 100 Male Female RESULTS 80 Parents surviving the following winter (%) – Which may lead to trade-offs between survival and reproduction 60 40 20 0 CONCLUSION Reduced brood size Normal brood size Enlarged brood size The lower survival rates of kestrels with larger broods indicate that caring for more offspring negatively affects survival of the parents.

More is Better? • Some plants produce a large number of small seeds – Ensuring that at least some of them will grow and eventually reproduce

Fewer is Better? • Other types of plants produce a moderate number of large seeds – That provide a large store of energy that will help seedlings become established

Demography • Study of the vital statistics of a population – And how they change over time • Death rates and birth rates • Zero population growth – Occurs when the birth rate equals the death rate

Exponential Population Growth Population increase under idealized conditions No limits on growth • Under these conditions – The rate of reproduction is at its maximum, called the intrinsic rate of increase

Example-understanding growth Question: I offer you a job for 1 cent/day and your pay will double every day. You will be hired for 30 days. Will you take my job offer? Answer: If you said YES, you will have made $~21 million dollars for 30 days of work. How is this possible? ? ?

1 ST DAY OF WORK: 1 cent pay/day 30 TH DAY OF WORK: ~10. 2 million/day Amount of Pay/Day How is this possible? ? ? # of Days

Exponential Growth Model *Idealized population in an unlimited environment *Very rapid doubling time; steep J curve *r= N=(b-d)N t r=instrinsic rate of growth d. N dt rmax. N

Exponential Growth in the Real World • Characteristic of some populations that are rebounding 8, 000 Elephant population 6, 000 4, 000 2, 000 0 1900 1920 1940 Year 1960 1980 –Cannot be sustained for long in any population

Logistic Population Growth • More realistic model of population growth • Carrying capacity (K) – Is the maximum population size the environment can support • In the logistic population growth model – The per capita rate of increase declines as carrying capacity is reached

Logistic Population Growth – Produces a sigmoid (S-shaped) curve 2, 000 d. N dt Population size (N) 1, 500 1. 0 N Exponential growth K 1, 500 Logistic growth 1, 000 d. N dt 1. 0 N 1, 500 (K N ) d. N rmax N dt K 0 0 5 10 Number of generations Figure 52. 12 15

The Logistic Model and Real Populations – Fits an S-shaped curve 1, 000 800 Number of Paramecium/ml • The growth of laboratory populations of Paramecium 600 400 200 0 0 5 10 15 Time (days) (a) A Paramecium population in the lab. The growth of Paramecium aurelia in small cultures (black dots) closely approximates logistic growth (red curve) if the experimenter maintains a constant environment.

Logistic Growth and The Real World • Some populations overshoot K Before settling down to a relatively stable density 150 Number of Daphnia/50 ml – 180 120 90 60 30 0 0 20 40 60 80 100 120 140 160 Time (days) What type of feedback loop is this? (b) A Daphnia population in the lab. The growth of a population of Daphnia in a small laboratory culture (black dots) does not correspond well to the logistic model (red curve). This population overshoots the carrying capacity of its artificial environment and then settles down to an approximately stable population size.

Logistic Growth and the Real World 80 • Some populations Number of females – Fluctuate greatly around K 60 40 20 0 � 1975 � 1980 � 1985 � 1990 � 1995 � 2000 Time (years) (c) A song sparrow population in its natural habitat. The population of female song sparrows nesting on Mandarte Island, British Columbia, is periodically reduced by severe winter weather, and population growth is not well described by the logistic model.

Natural selection (diverse reproductive strategies) a) Relatively few, large offspring (K selected species) b) Many, small offspring (r selected species) (K selected species) (r selected species)

Populations Regulated Biotic and Abiotic Factors Two general questions we can ask about regulation of population growth 1. What environmental factors stop a population from growing? 2. Why do some populations show radical fluctuations in size over time, while others remain stable?

Competition for Resources • In crowded populations, increasing population density – Intensifies intraspecific competition for resources 4. 0 3. 8 Average clutch size Average number of seeds per reproducing individual (log scale) 10, 000 100 3. 6 3. 4 3. 2 3. 0 2. 8 0 0 10 100 Seeds planted per m 2 (a) Plantain. The number of seeds produced by plantain (Plantago major) decreases as density increases. 0 10 20 30 40 50 60 70 Density of females (b) Song sparrow. Clutch size in the song sparrow on Mandarte Island, British Columbia, decreases as density increases and food is in short supply. 80

• Many vertebrates and some invertebrates are territorial – Territoriality may limit density

Territoriality: Ocean birds – Exhibit territoriality in nesting behavior

Health Population density. Can influence the health and survival of organisms In dense populations, pathogens can spread more rapidly

Fluctuations in Population Size • Extreme fluctuations in population size – Are typically more common in invertebrates than in large mammals Commercial catch (kg) of male crabs (log scale) 730, 000 10, 000 1950 Figure 52. 19 1960 1970 Year 1980 1990

Population Cycles 160 Snowshoe hare 120 Lynx 9 80 6 40 3 0 1850 1875 1900 Year • Influenced by complex interactions between biotic and abiotic factors 1925 0 Lynx population size (thousands) Hare population size (thousands) • Many populations undergo regular boom-and-bust cycles

Human Populations • No population can grow indefinitely and humans are no exception 6 4 3 2 The Plague 1 0 Figure 52. 22 8000 B. C. 4000 B. C. 3000 B. C. 2000 B. C. 1000 B. C. 0 1000 A. D. 2000 A. D. Human population (billions) 5

Global Carrying Capacity • Just how many humans can the biosphere support? • Carrying capacity of earth is unknown…. http: //www. youtube. com/watch? v=9_9 Sut. Nmf. Fk http: //www. youtube. com/watch? v=UUOEc. Nomakw&feature=rec -LGOUT-exp_fresh+div-1 r-8 -HM http: //www. youtube. com/watch? v=4 B 2 x. Ov. KFFz 4&feature=relat ed

• Age structure is commonly represented in pyramids Rapid growth Afghanistan Male Female 8 6 4 2 0 2 4 6 8 Percent of population Figure 52. 25 Age 85 80– 84 75– 79 70– 74 65– 69 60– 64 55– 59 50– 54 45– 49 40– 44 35– 39 30– 34 25– 29 20– 24 15– 19 10– 14 5– 9 0– 4 Slow growth United States Female Male 8 6 4 2 0 2 4 6 8 Percent of population Age 85 80– 84 75– 79 70– 74 65– 69 60– 64 55– 59 50– 54 45– 49 40– 44 35– 39 30– 34 25– 29 20– 24 15– 19 10– 14 5– 9 0– 4 Decrease Italy Female Male 8 6 4 2 0 2 4 6 8 Percent of population

Infant Mortality and Life Expectancy • Infant mortality and life expectancy at birth 50 40 30 20 60 40 20 10 0 Figure 52. 26 Life expectancy (years) Infant mortality (deaths per 1, 000 births) – Vary widely among developed and developing countries but do not capture the wide range of the 60 80 human condition Developed countries Developing countries 0 Developed countries Developing countries

Search for the Missing Sea Otters Case Study in Population & Community Ecology

Sea Otters Enhydra lutris

Otter Behavior http: //www. youtube. com/wat ch? v=d. Q 2 Lrnr 0 g. Lc http: //www. youtube. c om/watch? v=YQXKy TWMvp. M

Population Distribution

GROUP QUESTION: 1) What is happening to sea otter populations at several locations in the Aleutian Islands, Alaska? 2) What factors could be contributing to such a rapid change in the size of sea otter populations? Create a list of possible factors.

Could the otters simply have migrated from one part of the region to another? To find out, the researchers analyzed populations over a 500 -mile-long stretch of the Aleutians from Kiska to Seguam …. By 1993 otter numbers in that whole stretch had been cut by half. Here the geographical scope of the research effort became critical; a smaller region would not have been large enough to reveal the decline. In 1997, they … found that the population decline had worsened, to about 90 percent …. “That told us for sure it was a very large-scale decline, but we were still trying to understand the cause, ” Dr. Estes said …. The researchers … ruled out reproductive failure. Their studies enabled them to keep track of how often otters gave birth and how many young survived, and this revealed that reproduction was continuing to re-supply the population. With other possible causes eliminated, … mortality had to be the explanation. In the past, they had seen temporary declines in otter populations because of starvation, pollution or infectious disease. “In all those cases, ” Dr. Estes said, “we find lots of bodies. They get weak and tired and come ashore to die. ” This time not a single dead otter was found—a clue, he said, that “something really weird was going on. ” (Excerpted from Stevens, William K. “Search for missing sea otters turns up a few surprises. ” New York Times, January 5, 1999. ) Group Question: Read above and eliminate some of the reasons for changes in the relative abundance of sea otters at several locations in the Aleutian Islands, Alaska? What does it have to be?

Orca or Killer Whale Orcinus orca

Male vs. Female

Orca prey

Orca predation behavior https: //www. youtube. com /watch? v=yp. Ng 19 et. Jg 0 http: //www. youtube. com/w atch? v=Ks 40 wor. W_g. Q (hunting sea lions) Orcas & learned hunting behavior? (great white sharks? ? ) : http: //www. youtube. com/watch? v=SS 6 Njd. GLVZs &feature=related

Group Questions 1. Make a list of the types of information about killer whales you believe the scientists might need to test their hypothesis that increased predation by the whales was the cause of the sea otter decline. 2. Describe two experiments that would allow you to test the hypothesis that increased predation by killer whales was the cause of the sea otter decline. Keep in mind the following key components of any good experiment: a control (something to which to compare the treatment), replication (do it more than once), and consideration of confounding factors (what might cause differences other than what you manipulate in your experiment? ).

Group question: Interpret the two figures. What do they show? How does this provide evidence that orcas were responsible for the decline in sea otters in Kuluk Bay?

Group question: Why do you think Orcas started eating Sea Otters? Generate a list of possible ideas.

Why did Orcas start eating Sea Otters? • Fish community of the Bering Sea: – Past: – Ocean perch & herring – High abundance – Very high oil content

Why did Orcas start eating Sea Otters? • Fish community of the Bering Sea: • Present: – Pollock – High abundance – Low oil content

Why this change in species composition? • Where did the herring & perch go? ? ?

What were Orcas eating before? Harbor Seals Stellar Sea Lions on Amak Island

Population decline

Why care about Sea Otters? ? • Habitat:

Giant Kelp Forest

Biodiversity Sea urchins (Echinoderms)