Lecture – Populations Properties Estimation of Size Population Growth

1. Lecture – Populations Properties Estimation of Size Population Growth

2. What is a population? • ‘members of a particular species that inhabit a particular area’ • Various aspects: • Range and distribution • Size • Density • Age structure • Growth • Genetic uniqueness  subpopulations (ecotype)

3. Size of Populations • Abundance: number of individuals within a specified area • Abundance/area = Density • How do we determine how many individuals there are? • Two primary techniques: • Capture-mark-recapture • estimate of total population = (total number captured (second time) x number marked) / (total number recaptured with mark) • sampling

4. Estimation of population sizes • Choice of technique depends on • motility of target species • Nature of habitat • Resources • Resolution required • Generally rely on statistical sampling /various assumptions • http://www.pwrc.usgs.gov/monmanual/approaches/popsize.htm

6. Population growth rate: • Discrete-time • Geometric growth • Species which have discrete breeding seasons • Continuous time • Exponential growth

7. Geometric Growth: • N(t+1) = N(t) λ : at each interval of time population grows by the multiple λ • Exponential Population growth • logeλ = r Change over time Intrinsic rate of increase • Growth rate = dN/dt = rN No. of individuals in a population • The actual rate of population increase is Birthrate Deathrate Net immigration • r = (b – d) + (i – e) Net emigration

8. Geometric Growth – with discrete reproductive seasons • Estimate population at same time in each year • Mortality of young

9. Log population size increasing exponential against time produces straight line Slope (at any point) = dN/dt = rN

10. Logistic Population Growth

11. Carrying Capacity • No matter how fast populations grow, they eventually reach a limit • This is imposed by shortages of important environmental factors • Nutrients, water, space, light • The carrying capacity is the maximum number of individuals that an area can support • It is symbolized by k

12. As resources are depleted, population growth rate slows and eventually stops: logistic population growth. • Sigmoid (S-shaped) population growth curve.

13. K – N ( ) • dN/dt = rN K = rN(1-N/K) Growth slows as N approaches value of K or as (1-N/K) approaches 0

14. Limits to Population Growth • Environment limits population growth by altering birth and death rates. • Density-dependent factors • Disease, Resource competition • Density-independent factors • Natural disasters

15. Song sparrow • Density-dependent effects • Competition for resources • food • Suitable habitat – example: nesting sites • Effects that are dependent on population size and act to regulate growth Reproductive success decreases as population size increases • These effects have an increasing effect as population size increases

16. Density-independent effects • Effects that are independent of population size but still regulate growth • Most are aspects of the external environment • Weather • Droughts, storms, floods • Physical disruptions • Fire, road construction

18. Where is a species found? • Range: Geographical boundaries a species occupies • Determined by basic ecological parameters • No indication of distribution or abundance • Fundamental niche: • Indication of parts of habitat in which a species may be found • Typically patchy locally aggregated) w/i range • Realized niche: • Portion of fundamental niche in which species is actually found

19. Factors which impact range: • Physiological adaptations • Available food, nesting sites, etc. – factors which define suitable habitat • Predators • Competition – competitive exclusion principle – to be discussed later • Chance – past climatic and physiological events • Species could/does survive elsewhere, has not been introduced • Current and past climate influences all these things

20. Example: • Range of Canyon Wren • Distribution: • ‘confined to areas with rock faces’, canyons, bluffs

22. Fundamental niche: • Indication of parts of habitat in which a species may be found • Typically patchy locally aggregated) w/i range • Realized niche: • Portion of fundamental niche in which species is actually found

24. Patchiness and Subpopulations • Metapopulations – Local Populations (demes) in suitable habitat isolated in matrix of unsuitable habitat • Source/Sink Populations – source population over-reproduces, sink absorbs population • Landscape – Metapopulations linked in matrix of varied quality

27. Marmots on Vancouver Island • Unique species – isolated populations in cleared areas – impacted by fire/forestry practices • Loss of local populations results in fewer ‘stepping stones’ – genetically isolated metapopulations • Loss in genetic diversity • Movement between populations maintains variability within species • Important to continued viability of species • From: http://www.marmots.org/notes_vim.html

28. Ecotypes • Sub-populations adapted to particular local environments • Unique genetic make-up? • Same species • Common Garden Experiment • Seed collected from plants of same species growing in different environments grow in same location(s) (p 282) • Isolation may lead to differentiation into different species – uniquely adapted to specific environments –( see p 200)  restricted range