SBI4U Population Dynamics

1. SBI4U Population Dynamics Characteristics of Populations

3. Population Dynamics • Population ecologists • Monitor • Quantify • Monitor changes • Monitor interrelationships between species • Assess health of individual species and ecosystems • Develop policies and plans to save species from extinction

4. What is a Population? • Population: a group consisting of members of the same species that live together in a certain area at the same time • Populations live in a particular habitat, that provides them with the resources they need • Community: consists of all populations of all species that live and interact in the same area • Ecosystem: A community plus it’s abiotic environment • Population Dynamics: the study of changes in populations

5. Populations • Ecologists use quantitative measurements to study, predict, and describe populations • Can you think of any examples? • Size • Density • Distribution • Life history

6. Terminology • Brainstorm with your lab partner to define the following terms in your own words AND provide an example. • Population size (N) • The number of individuals of the same species living within a specific geographical area. • Population density (Dp) • Number of individuals of the same species that occur per unit of area or volume.

7. Can you determine the population size?

8. Characteristics of Populations – Population Density • Who cares how big or dense a population is? • The density of a population can be related to how healthy the population is. We will talk about this and what influences population size/density in more detail later.....

9. measuring Population Size and Density • How do we determine the human population? • Can we use the same methods with other species? Why or why not? • Instead of counting individuals in a populations inefficiently, ecologists estimate population size by studying smaller samples  extrapolation • 3 methods: • Transects • Quadrats • Mark-Recapture

10. Transects Transect– a long line or narrow area used for population sampling • Researchers choose a line of specific length (i.e. 100m) • Walk along the line and count number of individuals of each species being monitored within the area • For sessile organisms – within 1m • Mobile organisms – within 50m Example: http://www.countrysideinfo.co.uk/wetland_survey/transec1.htm

11. Transects Useful for: • low population densities or • larger organisms like trees

12. Quadrats Quadrat – a box used to sample a population • Location is chosen at random • Quadrat is drawn  area can be large or small depending on size of species under study (A) • Number of individuals are counted within quadrat boundaries (N)

13. Quadrats • Information can be used to calculate population density: DP = N/A Sample Problem: • Ecologists are sampling the distribution of flowering white trillium plants in a section of forest covering 100m x 100m (so what is the area)? • They place four 1m by 1m quadrats randomly • They find 5, 4, 3, and 1 individuals in the four quadrats Calculate the population density 

14. Quadrats The calculated population density can be used to determine the estimated population size Estimated Population Size = DP x total study area What is the estimated population of trilliums?

15. Quadrats What type of species do you think this method would be most useful for? Useful for: • Sessile organisms or • Organisms with low motility

16. Mark-Recapture • Animals are captured • Then, marked with a tag/collar/band • Released back into their habitat • Recaptured at later time (days/weeks)  Watch this capture Data is used to estimate the population size according to the following formula: Population size (N) = M (number originally marked) x n (total individuals in recapture)/ m (marked individuals in recapture)

17. Mark-Recapture Sample Problem 1 A group of researchers captured 20 warblers, which were marked with leg bands. They were released soon after. One week later, 50 warblers were captured. Of the 50 birds, 10 had bands on them. What would be their estimated population size?

18. Mark-Recapture What type of species do you think this method would be most useful for? Useful for: Highly mobile populations

19. Population Dispersion • Dispersion:The population dispersion for a species is the pattern in which individuals in a population are distributed or spaced throughout an area. • Often related to density • Clumped Dispersion: occurs when individuals are concentrated in specific parts of the habitat • Often due to patchy resource distribution • May be social benefits ie. schooling fish

20. Population Dispersion • Uniform Dispersion: Individuals are spaced evenly throughout the habitat • Often due to intense competition. Eg. Nesting, feeding or mating territoriality, toxins released by plant roots

21. Population Dispersion • Random Dispersion: The population is spread out in an unpredictable manner that is unrelated to the presence of others • Least common and hardest to observe • Resources are not often distributed randomly

22. DONE!

23. Hold up! Dispersal patterns • Resource distribution is uniform • Resource distribution is clumped • Resource abundance varies • Resource abundance is scarce • Resource abundance is abundant • Interaction between members of a population is positive • Interaction between members of a population is negative • Interaction between members of a population is random.