Population Ecology

1. Population Ecology

2. Learning Outcome • Define population and its parameter • Describe the approaches to estimate population density • Distinguish between potential and realized of natality and mortality • Distinguish between population distribution pattern • Explain the demographic technique

3. Population as a Unit of Study • Population • A group of organisms of the same species occupying a particular space at a particular time • Deme • Groups of interbreeding organisms, the smallest collective unit of a plant or animal population • Individual that have possible chances to mate with each other

4. Population as a Unit of Study • Population has group and not individual characteristics • Basic characteristics of a population: • Density (no/area; no/vol) • Size (numbers) of the defined area • Age structure (based on age distribution) of the population group • Dispersion (the spread of individuals in relation to one another)

5. Four basic population parameters emigration mortality natality DENSITY immigration

6. Density: no of organisms per unit area or per unit volume Natality: the reproductive output of a population (birth, reproduction) Mortality: the death of organisms in a population Immigration: the no of organisms moving into area occupied by the population Emigration: the no of organisms moving out of the area occupied by the population Immigration and Emigration = Migration

7. Population parameters • Population parameters affect population density

8. How to estimate population density? • Techniques differ between organisms such that the technique to estimate deer cannot be applied to plant sp. or barnacles or vice versa. • There are 2 fundamental attributes that affect and ecologists choice of technique for population estimation.

9. 1) Mobility • - based on movements of the organisms • Animal- mobile • Plant- sessile 2 attributes affecting the choices of estimation technique 2) Size - small animals/plants are usually more abundant than large animals/plants - Elephant vs ant population

10. Why do we need to estimate population density? • Estimates of population are made for two reasons: • To quantify nature 2. Allows for comparisons between different populations in terms of space and time measure

11. 1) Absolute density No of individual per area/ volume Important for conservation and management 2 approaches to estimate pop density 2) Relative density Comparative no of organisms Which area has more organism e.g, between area x and y Area x has more organism than area y

12. Absolute density • Total counts • Sampling methods a) Quadrat b) Capture-recapture method

13. Absolute density- Total count • Total counts - direct counting of populations. e.g: • human pop census, • trees in a given area, • breeding colonies can be photographed then later counted • in general, total counts are possible for few animals eg. cat, butterfly, grasshoppers, bugs.

14. Absolute density- sampling method • Sampling methods • to count only a small proportion of the population - sample • Using the sample to estimate the total population • 2 general sampling techniques: a) Quadrat b) Capture-recapture method

15. Absolute density- sampling method (quadrat) a) Quadrat • Definition – An ecological sampling unit consisting of a small • square area of ground within which all species of interest are • noted or measurements taken. • 2. Method- Count all individuals on several quadrats of known size, • then extrapolate the average count to the whole area by using • diversity index or relative density formula. • 3. Requirements: • area of the quadrat must be known • the pop in the quadrat must be determined exactly • iii) quadrat/s must be representative of the area • - achieved by random sampling

16. What is random sampling? Absolute density- sampling method (quadrat) • Done many times at different points within the habitat to give a large number of different samples. • Toss coin/or small objects into the square or draw lots • Usually carried out when the area under study is fairly uniform, very large, and/or there is limited time available. • The quadrate frame is placed on the ground (or on whatever is being investigated) and the animals and/or plants inside it counted, measured, or collected.

17. Absolute density- sampling method (capture-recapture) b) Capture recapture method Capture, marking, release, and recapture- important for mobile animals Why?-it allows not only an estimate of density but also estimates of birth rate and death rate for the population being studied Peterson method Involves 2 sampling periods: Time 1- Capture, mark and release Time 2- Capture and check for marked animals Time intervals between the 2 samples must be short because this method assumes a closed population with no recruitment of new individuals into the population between time 1 and 2 and no losses of marked individuals

18. What is the formula? Absolute density- sampling method (capture-recapture) Marked animals in 2nd sample = Marked animals in 1st sample Total caught in 2nd sample Total population size

19. e.g of capture-recapture method Absolute density- sampling method (capture-recapture) • Dahl marked trout in small Norwegian lakes to estimate the size of the population that was subject to fishing. • He captured, marked and released 109 trout, and in 2nd sample a few days later caught 177 trout, of which 57 were marked. • From the data, what is the estimate population size?

20. e.g of capture recapture method Absolute density- sampling method (capture-recapture) • By using the formula: Marked animals in 2nd sample = Marked animals in 1st sample Total caught in 2nd sample Total population size 57 = 109 177 Total pop size Total pop size = (109 x 177) 57 = 338 trout

21. Some index used in relative density: Relative density • Traps – no caught per day per trap – animals caught will depend on their density, activity and range of movement, skill in placing traps – rough idea of abundance – night flying insects, pitfall traps for beetles, suction traps for aerial insects • Fecal pellets – rabbits, deer, field mice – provides an index of pop size • Vocalization frequency – bird calls per 10 mins, can be used for frogs, cicadas, crickets • Pelt records – trapper records dates back 300 years – of lynx

22. Relative density • Catch per unit effort – index of fish abundance – no of fish per cast net or no of fish per 1 hour trawling • Questionnaires – to sportsmen (eg fish) and trappers • Cover - % ground surface covered – in botany, invertebrate studies of the rocky intertidal zone • Feeding capacity – bait taken – for rats and mice – index of density • Roadside counts – birds observed while driving standard distances

23. Natality • The production of new individuals by birth, hatching, germination or fission • 2 aspects of reproduction must be distinguished: i) Fecundity- Potential ii) Fertility- Realized

24. Natality- Fecundity vs Fertility • Fecundity-physiological concept that refers to an organism’s potential reproductive capacity ii) Fertility-ecological concept based on the no of viable offspring produced during a period time

25. Natality • E.g.: the potential fecundity rate for humans is 1 birth per 10 to 11 months per female in the childbearing ages • realized fertility rate for a human pop may be only 1 birth per 15 years per female in the child-bearing ages

26. Mortality • Biologists-interested not only in why organisms die but also why they die at a given age • Longevity-the length or duration of life • 2 types: i) Potential longevity ii) Realized longevity

27. Mortality- Potential longevity i) Potential longevity • The maximum life span of an individual of a particular sp is a limit set by the physiology of the organism, such that it simply dies of old age • However, organisms rarely live under optimum conditions-most die from disease, or eaten by predators or succumb to a number of natural hazards • Can be measured only in labs or zoos

28. Mortality- Realized longevity ii) Realized longevity • The actual life span of an organism • Shorten from the potential longevity • Can be measured in the field/nature • In nature, many circumstances can minimizes their life span e.g. competition, predation, disease and parasitism.

29. examples • European robin has an average life expectation of 1 year in the wild, whereas it can live at least 11 years in captivity • 1 yr in the wild= realized longevity • 11 yrs in captivity= potential longevity

30. Population dispersion patterns random 3 types clumped uniform

31. Population dispersion pattern

32. Population dispersion pattern- random, uniform • Random-when the position of each individuals in a pop is independent of the others • Example: plant population b) Uniform-it results as a form of some negative interactions • Common among animal pop where individuals defend an area for their own exclusive use (territoriality) • Example: penguin, lion population

33. Population dispersion pattern- clumped c) Clumped-where individuals occur in groups • Example: herd of cow, school of fish • Reason- suitable habitat or resources may be distributed as patches on a larger landscape

34. DEMOGRAPHIC TECHNIQUES Patterns of survival

35. Patterns of Survival Three main methods of estimation: 1) Cohort life table Identify individuals born at same time and keep records from birth. 2) Static life table Record age at death of individuals. 3) Age distribution Calculate difference in proportion of individuals in each age class. Assumes differences from mortality.

36. Cohort Life tables • It is based on a single year class or cohort (e.g., all animals hatched or born in 2000). • We keep track of those individuals and recount them yearly, keeping records on them from birth to death • The cohort life table approach is generally not feasible for very longlived species

37. e.g of cohort life table for the song sparrow

38. Static (Vertical) Life Table Based on Living Individuals • Record the age at death of a large number of individuals • The individuals in this sample were born at different times

39. The age of which individuals die • Tagging the newborn, recovering the tag after death and record the age at death • Estimation method: i) Mountain sheep- can be aged by counting the growth rings on their horns ii) carapaces of turtle iii) trunks of trees

40. Age Distribution Age distribution of a population reflects its history of survival, reproduction, and growth potential. Miller published data on age distribution of white oak (Quercus alba). Age distribution biased towards young trees. Sufficient reproduction for replacement. Stable population

41. Age Distribution

44. Population Age Pyramids

45. Survivorship curve summarizes the pattern of survival in a population

46. Type 1- high survival in early and middle life, followed a rapid decline in survivorship in later life e.g: Humans and large mammals, dall sheep, annual plant, rotifer Type 2- constant mortality rate is experienced regardless of age e.g: birds, squirrels, turtle, white-crowned sparrow, song bird Type 3- Greatermortality rate at early in life, followed by a period of much lower and relatively constant loss e.g: Fishes, invertebrates, parasites, perennial plant