Timing of arrival. Krakatoa (Krakatau) dispersal types. Timing

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1 Dispersal and colonization of habitats Colonization of a site: dispersal adaptations requirements sequence r and K strategy Consequences More examples Example Location: present Indonesia, island of Krakatoa The 1883 eruption ejected more than 25 cubic kilometers of rock, ash, and pumice The explosion destroyed completely life on the volcano and adjacent islands. A new cone formed and its ecological development was monitored, with decent ecological surveys made as early as Example Only fraction of the surface is alive Colonization and development of communities was interrupted several times 1

2 Krakatoa (Krakatau) dispersal types Ridley s dispersal classification on the then known floras on Krakatau (up to 1919 only), Christmas Island and Cocos- Keeling Dispersal type Krakatau Christmas Cocos Sea borne Wind Berry or drupe Adhesive Mud on birds Doubtful Total Pteridophyta After Whittaker et al Timing The colonization of the newly built Krakatoa island by plants & animals took 50 years; First: Hawaii (more isolated): one plant species every years, one land snail every years and one bird species every years These estimates are based on the average age of the islands being 5 million years Timing of arrival Category Sea dispersed flowering plants Animal dispersed flowering plants Wind dispersed flowering plants Ferns (all winddispersed) A shift from sea to animals 2

3 Empty space: primary sites Primary sites where no prior communities existed 5-20 years Ferns appear to dominate first settlers. Why? Empty space: secondary sites Secondary sites where new space opens at the partial expense of an old community New secondary site Implications: modified physical habitat, propagules Two steps: arrival and settlement Primary sites who arrives first? - transient animals - seeds or spores carried by wind or transient animals - small seeds before large ones What are typical properties of early arrivals? - small - resistant to high temperature, low humidity - adapted to fast or delayed germination - adapted to transport (burs, wings, hairs) - require light, i.e., no shade from other plants 3

4 Water Dispersal adaptations Fur Wind Consumer Ocean currents Non-consumers Hoarders Requirements Ability to survive travel in a physically demanding environment (rock, air, ocean, dry and hot mineral soil) Ability to survive germination or birth in the above Ability to reach reproductive maturity, or reproduce vegetatively, or parthenogenetically (animals) High reproductive rates, colonial nature (examples.?) e.g., beach creepers (vine like plants) Differential performance Who (plants) stays on site? Plant Characteristic Photosynthesis light saturation efficiency at low light photosynthetic rates Water use efficiency transpiration rates Seeds number size dispersal distance viability induced dormancy Root/shoot ratio Mature size Growth rate Value High Low High high High Small Large Long common low small high 4

5 r and K strategy Recall: r = net rate of N increase (speed). Thus: K = carrying capacity (~max N). Thus, if there is a limit: From this: If N is small, a species must grow fast; if N is near K, it should keep it without large fluctuations N Pioneer communities dn rn dt Mature communities Time (t) dn K N rn dt K Invading plants grow quickly, and make lots of seeds ( r strategists). K strategists focusing their energy and resources on growth and long-term survival (usually come in later in the settlement of new habitat). General concepts Dispersal limitation: limitation of distribution or abundance because of either constraints on dispersal or inadequate production of dispersing individuals. Resultant community Initial community Recruitment limitation: limitation of distribution or abundance because of either constraints on survival of individuals that arrive or were born at a site (local filter). How would we demonstrate it empirically? Things may become complicated Just for fun 5

6 Seedlings Seeds Predation rate Things may become complicated Propagules (young, seeds) are often easy, nutritious and abundant food for other organisms Their survival should thus depend on: Kinds of predators Number of predators Pattern of foraging Payoffs from foraging (number of propagules predator can find) Attalea butyracea Theory Distance from parent tree Number of seeds Distance from parent tree However 6

7 Seedlings Seeds Predation rate Results Distance from parent tree Number of seeds inverts agoutis squirrels Distance from parent tree Thus, a complex system emerges Agouti (attack high densities) - Red-tailed squirrel (attack low densities) - Seed density or health - Seedling density + Invertebrates - + What is a site anyway? 7

8 Differential performance Who arrives in greatest numbers? - those that are close - those that are more numerous - those that more mobile Likely candidates Small insects and arachnids (young spiders, mites) Also, small birds and mammals if site is not very isolated 3 months old lava flow 10 years 15 year old lava flow 20 year old lava flow Effects of scale What if the site is large (relative to dispersal distance? Diagrammatically.. Role of monkeys, parrots 8

9 Effects of scale What if the site is large (relative to dispersal distance? spatial waves; short distances from the source site if: a) dispersed by tree animals (monkeys, birds, bats) that do not enter open areas) b) seeds belong to K-strategists (heavy, adapted to germinate in shady understory) These are patterns produced by dispersal limitation Effects of scale What if the site is small (relative to dispersal distance? Recolonization will be synchronous throughout the site Other consequences of new sites Consider the case of forest regeneration after logging Rich structure, multiple levels Same age; simpler structure 9

10 After Pickett et al. Dispersal initiates another process (succession) Vegetation dynamics Inspection of right-hand lists alerts to the fact that all these phenomena, factors, or constraints depend on the area and time considered (scale-dependence) Site availability Species availability Species performance Initial coarse disturbance Dispersal Propagule pool Resource availability Stress Life history Ecophysiology Competitors Allelopathy Consumers Soil Microclimate Identity Cycles Defenses Patchiness Size Severity Dispersion Agents Landscape Decay rate Land use Climate Prior occupants Allocation Reproductive timing Reproductive mode Germination Assimilation Growth rate Identity Consumers Fine-scale disturbance Resources Soils Microbes Neighbors 10