Population Dynamics Exam 2
1. When would you choose to use an age structured model and when would you use a stage structured model instead?

Age Structured: Equal time intervals • All surviving individuals progress to the next time step t = 0, 1, 2, 3, 4, 5, 6….x

      Deer or humans.

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Stage Structured: Individuals are difficult to age • Demographic characteristics (fecundity, survival) are relatively consistent within discrete ‘stages’.

      Salamanders or frogs.

 

For humans, age is a meaningful descriptor of an individual • For many wild pops, vital rates (i.e. reproduction & survival) depend on developmental, morphological or behavioral stages • Stage is often more easily identified in field than age

2. Discuss the difference between the transition matrix elements for stage-based vs. age-based population models.

Age-Based (Leslie Matrix): Each individual will move on to the next age class no matter what. This means the fecundity will be present each step.

Stage-Based (Lelfovitch Matrix): Each individual may or may not move on to the next stage each time step. And so each amount that does and does not move on needs to be accounted for. Fecundity will only be accounted for at the adult stage.

3. Given a set of fecundity and survival rates be prepared to construct a transition matrix.
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4. Given a simple Leslie matrix and age structured population (vector), be able to calculate the age-structured population for the next time step.
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5. As used in the Leslie matrix how is fecundity defined?

• Each element in top row represents fecundity (Fx) for that age group – Combination of mj (maternity) and p j (survival) of newborns.

 

Fecundity = # young produced that survive to next time step

 

           Fx = # young produced / # adults of age x  OR  Fx = # daughters produced / # females of age x

6. Distinguish between the following measures of reproduction: maternity (also known as natality or fertility), fecundity, and recruitment (as I defined them in the class notes).

Maternity (natality, fertility) – average # offspring born/female that reproduces (litter size, clutch size).

Fecundity – average number of offspring born per individual of a given age (or stage) surviving until the next age – product of maternity & proportion of the cohort that breeds.

 Recruitment ? net population production after both births & deaths accounted for. May include only female offspring.

7. Discuss how skewed sex ratios affect populations for monogamous and polygamous species.

Monogamous – population growth declines with a departure from 1:1 ratio for either sex. Skewed sex ratio means some wont get to breed if its not even.

 

 Polygamous – effect depends on which sex declines because it is a function of number of breeding aged females. Take deer, one male breeds with many females. Drop in females means less young while drop in males inconsequential.

8. Using vernal pool breeding salamanders as an example, discuss why biased sex ratios may be difficult to detect.

Males and females have different migration patterns for breeding. Males stay while females travel = more mortality in females. Or males leave soon after breeding while females stay = a sample appears that there are more females. Some can change sex later?

9. What are some measures of reproduction that can be used for mammals? Birds? Reptiles and amphibians?

Birds : • clutch size • hatching success • young fledged.

 

Mammals:  • litter size • juvenile numbers • corpora lutea scars.

 

Herps: • clutch/egg mass size • hatching success • # of larvae/hatchlings • # of metamorphs.

10. What is net reproductive rate and how is it calculated?

Average # of female offspring produced by each female during her life.

 

Equation: R0 =  ? l fx bfx

                 

The sum of lx (proportion of original cohort that survives to start of age x) times bx (# of female offspring produced by adult females of age x).at each time interval.

 

11. What does “reproductive value” represent and why is it important for population management? Understand how the concept of reproductive value can be used in developing strategies for population reintroductions or in culling a herd to prevent overpopulation.

The relative number of offspring that remain to be born to individuals of a given age

 

 # offspring produced by individuals of age x or older / # individuals of age x

 

Age that produces most offspring (highest reproductive value) is the one that should be saved/culled the most.

12. Distinguish between standing crop and cohort data.

Cohort – a group of individuals born at the same time: “year class”. Data followed through time. More difficult.

 

Standing Crop – a count of all individuals by age class at one point in time. Can be used to determine cohort if recruitment and survival rates constant.

13. Under what condition(s) can standing crop data be substituted for cohort data?

Can be used to determine cohort if recruitment and survival rates constant.

14. What is the difference between survival and survivorship as used in a life table? Given a life table, be able to calculate age-specific survival and survivorship rates.

Survivorship is the proportion of the original number of individuals in the cohort that are still alive at the beginning of age x.

 

Survival rate, which is the probability of surviving from a given age to the next, whereas survivorship is the probability of surviving from birth to a given age.

 

Calculate survivorship by n(x)/n(0).

Calculate survival rate using S(x) = l(x+1) / l(x).

 

15. Discuss the difference between type I and type III survivorship curves and give an example for each.

Type I ? humans & other mammals that invest much in their offspring

 

 Type II – rare, some birds but with more mortality at egg & chick stages

 

Type III – many insects, marine invertebrates & flowering plants

16. What is generation time?

Average age of reproduction or the average age of the parents of all the offspring produced by a single cohort

17. Distinguish between a stable age distribution and a stationary population. Given a table of age-structured population numbers for multiple time steps be able to determine whether the population has a stable age distribution and whether it is a stationary population.

Stable age distribution ? proportions of individuals in each age group are constant

 

Stationary age distribution ? proportions of individuals in each age group are constant AND constant population size

18. Why was the Mayfield Method developed for calculating nest success?

How many nests survived a breeding season? Used to estimate survival from a cohort of nests when data are missing. – Nests typically not found until after incubation begins – Typically not checked daily. How many nests were initiated & failed before you found them? Exact date of failure?

19. Explain the concept of metapopulations and the linking processes that drive them. Provide at least two real world examples of metapopulations.

• A “regional” population made up of two or more “local” populations.

 • Discontinuous in distribution – distributed over spatially disjunct habitat (patches)

• Movement among local populations occurs but is not routine, usually due to intervening unsuitable habitat (matrix)

 

Linking processes: • Extinction • Colonization • Population turnover

 

Examples are salamanders in vernal pools and spotted owl habitats.

20. What are the metapopulation processes that serve to maintain local populations over time?

• Supplementation (“rescue effect”)

• Gene flow

 • Re?colonization

 

21. What are the four factors that affect metapopulation dynamics?

• Number & geographic configuration of habitat patches

• Similarity of environmental conditions for various patches

• Dispersal patterns

• Interaction between environmental conditions & dispersal patterns

22. What are the four elements that Hanski uses to define a metapopulation?

1. Local breeding populations occur in “relatively discrete” habitat patches (spatially structured)

2. No local population is so large that its life expectancy is long relative to the metapopulation

3. Dynamics of local populations are sufficiently asynchronous so simultaneous extinction of all local populations is unlikely

4. Habitat patches are not so isolated that recolonization is prevented

 

23. What is the rescue effect?

? occurs when a local population is saved form extinction by immigration from other local populations (e.g. from sources to sinks)

24. Why is it so important for a biologist to distinguish between source and sink populations and their relationship with each other?

Only a small proportion of the total population may be located in source habitat (measures of population density can be misleading; need to evaluate demographic characteristics of population)

 

Adding habitat to a reserve may result in a smaller metapopulation if most of the additional land is sink habitat

26. Discuss the effects of environmental correlation and dispersal patterns on extinction rates of metapopulations.

Greater correlation and dispersal = greater risk of extinction over time.

27. Briefly discuss the primary trade-offs (positive and negative consequences) of how the proximity of (distance between) subpopulations may affect the long-term viability of a metapopulation.

Greater proximity (farther they are), the less enviro correlation and more survival against natural disasters. BUT farther means more dispersal which means less survival when dispersal needed.

28. What is the SLOSS debate and how is it relevant to decisions about reserve design?

Should a reserve design emphasize a Single Large habitat patch Or Several Small patches. Depends on what species but over all big, less divided, more circular is always better.

29. Discuss the concept of rarity and explain how a locally abundant species could be considered rare.

Based on three factors and having one will make it rare.

 

Geographic Range: • Species near the limits of their geographical ranges or habitat spectra

Population Size: • Species that exist at low population densities wherever they occur

Habitat Specificity: • Species that specialize on certain types of patchily? distributed habitats


Locally abundant over a large range in specific habitat, Locally abundant in several habitats but restricted geographically, or Locally abundant in a specific habitat but restricted geographically

30. What are the three hypotheses/theories that have been proposed to explain the observed species-area relationship on islands? Be able to briefly explain each of these hypotheses.

Habitat Diversity Hypothesis – Larger islands contain a higher diversity of habitats and therefore support more species.

 

Passive Sampling Model –  • Islands function as passive targets for immigration that randomly accumulate individuals

 • Large islands would be expected to accumulate more species by chance alone.

 

Equilibrium Theory –  Once an island is at its equilibrium for a particular taxa group, the rate at which species are lost  =  the rate at which unrepresented species colonize the island

 

31. Explain the various processes that affect species diversity according to island biogeography theory. How does distance and area affect these processes?

Area Effect:  • Smaller islands support smaller populations • The probability of a species going extinct increases with smaller population sizes  

 

Distance Effect • The more isolated the island, the less likely colonization will occur. • Thus, distance acts through immigration rates to limit the number of species

32. Explain why different taxa (i.e. birds, mammals, herptiles) have different vulnerabilities to habitat fragmentation.

• Dispersal is greatly enhanced in the flying taxa over the non?flying taxa

• Lower metabolic rate of ectotherms allows for higher population densities, thus less vulnerability to extinction than endotherms

• Larger body size + higher metabolic demands also lead to lower densities

33. Why might birds and bats not be good choices for testing whether species-area relationship found on islands also apply to habitat patches?

They can fly, they may use areas between patches, and have more mobility.

34. Extinction is a natural process so why should resource managers be concerned about extinctions today?

Rates of extinction above natural extinction. Current rate 1000 times faster than natural. 

35. Explain the concept of an “Extinction Vortex” and why it is an important considering when managing declining populations.

• Population levels decline due to some deterministic factor (e.g. over?harvesting)

 • Deterministic stressors are eliminated or reversed (e.g. regulation)

 • However, small populations remain vulnerable

Need to prevent deterministic factors from ever happening and is they do happen, then you need to be vigilant even after stressor relieved due to stochastic vulnerability.

36. What is Population Viability Analysis and how might a manager use one?

The quantitative branch of viability assessment The application of data and models to estimate likelihoods of a population crossing thresholds of viability within various time spans. Generally combine: • Field studies on important demographic parameters • Simulation modeling of the possible effects of various extinction factors.

 

Components: Criterion for viability (quasi?extinction threshold) – Extinction threshold – Quasi?extinction threshold (e.g. based on Allee effects) – Triggers for management action

• Time frame

 • Probability of reaching a threshold

 

Applications: • Planning research & data collection

• Assessing vulnerability

• Ranking management options

Not an exact science

37. Discuss the three components that are central elements of a Population Viability Analysis (PVA).

Criterion for viability (quasi?extinction threshold) – Extinction threshold – Quasi?extinction threshold (e.g. based on Allee effects) – Triggers for management action

• Time frame

 • Probability of reaching a threshold

38. Island species are generally more vulnerable to extinction than those that occur on continents. Which taxa have the greatest percentage of island extinctions and why are island species more vulnerable?

Birds have highest rate of extinction.

• Small restricted ranges – essentially 1 population

• Isolation ^vulnerability

       Predation – Disease – Low reproductive rates

39. Explain why we must consider both biological and social considerations when defining persistence for a species or population.

A value judgment by society is needed to determine the time frame to use in conservation planning, and the degree of security sought for the population being conserved.

 

40. Describe and distinguish among the following: polymorphism, heterozygosity, and allelic diversity.

Polymorphism: Occurrence of more than one allele for a gene within the subject population or subpopulation

 

Heterozygous: An individual having two different alleles for a particular gene.

Homozygous: An individual having two copies of the same allele for a particular gene

 

Allelic diversity: Average number of alleles per locus (Location of a gene on a chromosome)

41. What are the three fundamental levels used to measure genetic diversity?

• Within individuals – Fitness

 

 • Among individuals (within a population) – Fitness of progeny – Adaptive capacity

 

 • Among populations – Adaptation to local environmental conditions – Adaptive capacity

42. What is genetic drift?

The random changes in gene frequency, including loss of alleles, that is likely to  occur in small populations because each generation retains just a portion of the gene pool of the previous generation and that sample may not be representative.

43. What is inbreeding depression?

The loss in heterozygosity arising from mating of closely related individuals. Increases likelihood of recessive, non-desirable traits to be expressed because allele more common.

44. When might outbreeding be a problem for population conservation?

• Populations may be locally adapted to different environmental conditions – Offspring of parents from different populations are not well adapted to either location

 

 • Different populations evolve different coadapted gene complexes – Outbreeding can disrupt these gene complexes and decrease fitness

45. What is a bottleneck event and how does it affect population genetics? Under what conditions might a species that experiences a bottleneck maintain much of its genetic variability?

            A dramatic collapse of population numbers – sudden or gradual environmental change

A bottleneck is a sampling event – taking a relatively small sample of items, i.e. genes from a large population

 

Can recover after if low population numbers do not persist.

47. Describe the 50/500 rule of conservation genetics. What threats to small populations was the 50/500 rule created to address?

Ne = 50 to conserve genetic diversity during the short term (several generations) and to avoid inbreeding depression

 

Ne = 500 to avoid serious genetic drift in the long term

48. Be prepared to discuss the situation with Javan and Sumatran rhinos and to propose steps that you think should be taken to decrease the risk of extinction over the next 50-100 years.

Decline due to poaching and habitat loss. Captive breeding in home range is best. 

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