1. COMMUNITY CHANGE (SUCCESSION) Krebs cpt. 21; pages 403-424; 431

2. Connell and Slatyer 1977 Connell and Slatyer 1977 Succession driven by interactions between species:  FACILITATION  TOLERANCE (COMPETITION)  INHIBITION

3. Facilitation SUCCESSION PATHWAYS ABCD AB C D Tolerance & Inhibition

4. Succession models (Krebs 5 th Fig. 21.4) + + + + + + - - - o o o Species interactions + - o

5. FACILITATION …only certain pioneer species can establish after disturbance. Early species enhance the ability of later species to establish. INHIBITION …any species can invade. Once established, species resist further invasion and are displaced only by death or further disturbance. TOLERANCE …any species can invade. Early species have little or no effect on abilities of later species to invade. Later species can displace early species by reducing resources to levels below those tolerated by earlier occupants.

7. A study from abandoned farmland illustrates some aspects of Facilitation, Tolerance and Inhibition (see Krebs pp 419-422) FIELD ABANDONED IN FALL 1. INITIAL INVASION: Horseweed Horseweed a winter annual a winter annual produces abundant seed produces abundant seed self-allelopathic self-allelopathic Conyza canadensis

8. 2. NEXT SEASON: AstersAsters More susceptible to decaying roots of horseweed, than horseweedMore susceptible to decaying roots of horseweed, than horseweed Tolerant of dry conditionsTolerant of dry conditions

9. 3. SECOND AND THIRD SEASONS 3. SECOND AND THIRD SEASONS: BluestemBluestem Seedlings invading since initial abandonmentSeedlings invading since initial abandonment BroomsedgeBroomsedge Seedlings invading since initial abandonmentSeedlings invading since initial abandonment More tolerant of dry conditions than AstersMore tolerant of dry conditions than Asters Decaying roots of Horseweed promote growthDecaying roots of Horseweed promote growth

10. Bluestem Broomsedge

11. FACILITATION: Broomsedge is promoted by decaying roots of horseweed & aster TOLERANCE: Broomsedge displaces aster through competition for water INHIBITION: Horseweed litter prevents aster from persisting SUMMARY

12. FORCIER 1975 Succession driven by interaction of disturbance & life history traits of species Studied trees in a New Hampshire forest Trees with dbh >2 cm (400 plots) 90% of canopy: Sugar maple American beech Yellow birch

13. Eastern deciduous hardwood forests Several tree species

14. Grey Birch, Betula populifera Black Gum, Nyssa sylvatica

15. Red Maple, Acer rubrum Beech, Fagus sylvatica

16. YELLOW BIRCH SUGAR MAPLE BEECH r K

17. SPECIES Density (#/m 2 ) (d min /d max ) x 100 % plots with at least 1 seedling Mass/ind (mg) Yellow birch 21.32928 Sugar maple 105773268 Beech 3.96655569 Many small offspring (r-type) Fewer large offspring (K-type) Variable density and high dispersal More even density and lower dispersal

18. Number of cohort alive at beginning of interval Age interval Yellow birch Sugar maple Beech 0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 1000 70 <30 1000 583 317 225 166 118 84 54 48 42 1000 410 262 188 138 121 110 92 87 83

19. CANOPYSEEDLINGSSAPLINGS < 0.5m tall0.5 – 2 m tall Yellow birch Sugar maple Beech ++0++0 -+--+- Sugar mapleYellow birch Sugar maple Beech 0++0++ 0 ++ BeechYellow birch Sugar maple Beech 00+00+ 0 Sprouts + (seeds -) + = significantly present 0 = no relation - = significantly absent

20. CATASTROPHIC DISTURBANCE Yellow birch Sugar Maple Beech (seed) Beech (sprouts) MINOR DISTURBANCE Successional communities