Regulation and control of population size

1. Regulation and control of population size

2. Variation in Populations • Populations tend to vary in size over time and space. • Long-term records often reveal fluctuations that might be overlooked in shorter term

3. Infestation by chinch bugs in Illinois monitored over decades reveals populations fluctuations: • In some years, populations averaged 1000/m2 over an area of 300,000 km2 • In other years farmers reported little damage

4. Extremes of population control • Logistic population control (life is hard) • Logistic with time-lag (sins of the parents) • Density independence (stuff happens) • Plastic growth (if you’ve got it, flaunt it) • Disease & predation (watch your back)

5. Domestic sheep in Tasmania

6. David Lack - Density Dependent Regulation The case of the great tits

10. Maine Warblers • Winter flocks - spring territories; • Limit food by possible territories; • Surplus animals = social outcasts • Maine boreal forest; Insectivorous birds eat caterpillars; USDA & Fish & Wildlife Service experiment. • In 40 acres = 148 pairs, shot; After 2 weeks shot another 302 males, still territorial birds singing. • Second years 154 pairs 352 mails shot before gave up. No female replacement. Why? • Would this be true today?

11. Lack’s conclusions • Constant numbers, relatively speaking • Constant reproduction • Excess tend to waunder • Mortality is often in bad season or out of territory

12. Andrewartha and Birch Density independent control. • Austriocetes cruciata: South Australian grasshopper • Swarms in 1935-1939; 1940 went away • Mediterranean climate with uncertain spring rains. One generation per year, eggs diapause, 50 days to mature. Race against time to grow & reproduce. • Andrewartha & Birch watched them die in spring 1940

13. Fresh annual plant growth, and few others to exploit it. • Good times lead to massive breading & reproduction • Seaward (=moist): P/e = 1.0 in September (spring); • Inland (=dry): P/e = 0.25 October

14. Thrips imaginis • Black slivers on flowers of rose family plants (e.g. ornamental roses & apples); • If >=40, damage ovary on apple; • No diapause, active all seasons; eggs in flowers; pupae in ground; Summer especially bad season • Andrewartha and Birch observed 20 roses a day for 14 yrs = 6 million thrips • Warmth and wetness matter

15. STOP !! We have not gotten past this point in the lectures yet.

21. Relationship between density and yield in herbaceous plants. The “Law of constant final yield” Note that after a critical density is reached, yield is independent of density.

22. Plant weight as a function of plant density, and its change with plant growth

23. y=w.d 1/w = d(1/y) 1/w = Ad + B

24. Survivorship in 7 populations of Loblolly Pine established in 1925 in the Duke Forest.

26. G= { ΣiΣj |yi-yj| }/(2n**2)ybar all plants equal --> 0.0 ; all plant but one infinitely small --> 1.0

27. The -3/2 thinning rule w= c.p-3/2 area proportional to L2 weight proportional to volume proportional to L3 Therefore, area proportional to w2/3 and area proportional to 1/density Thus, weight = c.p-3/2

29. Natural thinning in loblolly pine populations of differing initial density.

31. Butterflies Erebia epipsodea Euphydryas aurinia Heliconius ethilla Euphydryas editha