COMMUNITY CHANGE (SUCCESSION) Krebs cpt. 21; pages 403-424; 431 Biol 302 succession
SUCCESSION …. Is the non-seasonal, directional and continuous pattern of colonization and extinction on a site by populations. Is the replacement of one kind of community by another kind; the progressive changes in vegetation and animal life that may culminate in the climax community (Krebs 622) Biol 302 succession
SECONDARY SUCCESSION …. … recovery of a disturbed site. PRIMARY SUCCESSION …. … recovery from a new sterile area that has been uncovered by a retreating glacier, or created by an erupting volcano. SECONDARY SUCCESSION …. … recovery of a disturbed site. Biol 302 succession
PRIMARY SUCCESSION Mt. St. Helens pp403-405 Lake Michigan dunes pp416-419 Biol 302 succession Glacier Bay pp413-416
SECONDARY SUCCESSION Krebs pp419-422 Biol 302 succession
Succession driven by interactions between species: Connell and Slatyer 1977 Succession driven by interactions between species: FACILITATION TOLERANCE (COMPETITION) INHIBITION Biol 302 succession
FACILITATION …only certain pioneer species can establish after disturbance. Early species enhance the ability of later species to establish. 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. INHIBITION …any species can invade. Once established, species resist further invasion and are displaced only by death or further disturbance. Biol 302 succession
A B D C A B C D SUCCESSION PATHWAYS Facilitation Tolerance & Inhibition A B D C Biol 302 succession
Biol 302 succession
FACILITATION TOLERANCE INHIBITION Biol 302 succession
FIELD ABANDONED IN FALL 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 a winter annual produces abundant seed self-allelopathic Conyza canadensis Biol 302 succession
More susceptible to decaying roots of horseweed, than horseweed 2. NEXT SEASON: Asters More susceptible to decaying roots of horseweed, than horseweed Tolerant of dry conditions Biol 302 succession
3. SECOND AND THIRD SEASONS: Bluestem Seedlings invading since initial abandonment Broomsedge More tolerant of dry conditions than Asters Decaying roots of Horseweed promote growth Biol 302 succession
Bluestem Broomsedge Biol 302 succession
Broomsedge is promoted by decaying roots of horseweed & aster SUMMARY 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 Biol 302 succession
Studied trees in a New Hampshire forest 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 Biol 302 succession
Eastern deciduous hardwood forests Several tree species Biol 302 succession
Grey Birch, Betula populifera Black Gum, Nyssa sylvatica Biol 302 succession
Beech, Fagus sylvatica Red Maple, Acer rubrum Biol 302 succession
YELLOW BIRCH SUGAR MAPLE BEECH r K Biol 302 succession
% plots with at least 1 seedling SPECIES Density (#/m2) (dmin/dmax ) x 100 % plots with at least 1 seedling Mass/ind (mg) Yellow birch 21.3 2 92 8 Sugar maple 10 57 73 268 Beech 3.9 66 55 569 Biol 302 succession
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 <30 583 317 225 166 118 84 54 48 42 410 262 188 138 121 110 92 87 83 Biol 302 succession
CANOPY SEEDLINGS SAPLINGS < 0.5m tall 0.5 – 2 m tall Yellow birch Sugar maple Beech + + 0 - ++ Seed - Sprouts + Biol 302 succession
CLIMAX MICROSUCCESSION Beech (sprouts) Beech (seed) MINOR DISTURBANCE Sugar Maple Yellow birch CATASTROPHIC DISTURBANCE Successional communities Biol 302 succession