Succession & Disturbance PDF

Lecture 21: Succession & Disturbance - Defining succession - Types of succession - Types of species involved in succession - Classic examples of primary succession - Agents of change (e.g., disturbances)  Semester Schedule Date Day Quiz Open Quiz D...

Lecture 21: Succession & Disturbance - Defining succession - Types of succession - Types of species involved in succession - Classic examples of primary succession - Agents of change (e.g., disturbances)  Semester Schedule Date Day Quiz Open Quiz Due Lecture Topic 22-Oct Tues 22-Oct 24-Oct 15 Life and the Physical Environment 24-Oct Thu 24-Oct 26-Oct 16 Origins of Evolution 29-Oct Tues 29-Oct 31-Oct 17 Speciation 31-Oct Thu 31-Oct 2-Nov 18 Phylogenies 5-Nov Tues Midterm 3 (Lectures 15-18): 4 lectures 7-Nov Thu 7-Nov 9-Nov 19 Community Structure 12-Nov Tues 12-Nov 14-Nov 20 Biotic Interactions 14-Nov Thu 14-Nov 16-Nov 21 Succession 19-Nov Tues 22 Trophic Structure 21-Nov Thu 23 Landscape Ecology and Conservation 26-Nov Tues 24 Review | buffer time 28-Nov Thu Thanksgiving (no class) 3-Dec Tues Midterm 4 (Lectures 19-23): 5 lectures 5-Dec Thu 25 Macroecology 10-Dec Tues 26 Global Environmental Change 17-Dec Tues FINAL (cumulative) 8-10am  Lecture 21: Succession & Disturbance - Defining succession - Types of succession - Types of species involved in succession - Classic examples of primary succession - Agents of change (e.g., disturbances)  Succession: Defined Succession is the change in species composition in communities over time Influenced by both biotic (living) and abiotic (non-living) factors (e.g., climate, soil, nutrients)  Succession: Change in species composition in communities over time (usually introduced as being directional) “beginning” “end”  Succession: Frederic Clements (1916) “Superorganism” Hypothesis Plant communities are groups of species working together toward some deterministic end. Succession is directional, always tending toward a “climax” community in any given area. “Climax communities” are stable and resistant to Alder trees following disturbance. forest harvest in BC  Succession: Henry Gleason (1917) “Individualist” Hypothesis Individual species respond to fluctuating environmental conditions. Community composition changes gradually. Communities are not a predictable and repeatable result of all species working Alder trees following together. forest harvest in BC Succession: Not a Simple Cycle! Let’s Simplify the Cycle Interactions often result in the replacement of one species with another.  Lecture 22: Succession & Disturbance - Defining succession - Types of succession - Types of species involved in succession - Classic examples of primary succession - Agents of change (e.g., disturbances)  Primary vs Secondary Succession Primary Succession: Occurs when bare land is settled for the first time by living organisms. Development of biotic community is slow. Examples: bare rock, shifting sand dunes, cooled lava, retreating glaciers, etc. Secondary Succession: Occurs in an area where life existed earlier but many species destroyed (soil remains largely intact). Development of biotic community is fast. Examples: abandoned farmland, burnt/cutover forest, windstorm, insect outbreak, etc.  Primary Succession: bare land Volcanoes: Mount Saint Helens, WA (1980) Glaciers Shifting Sand Dunes  Secondary Succession: intact soil Hurricanes and Fire Anthropogenic Severe Weather Influences “Old Field” Example: ________ Succession University of Florida Natural Teaching Area “Old Field” Example: Secondary Succession Newly abandoned field “Old Field” Example: Secondary Succession ~1 year after abandonment: grasses and weeds dominate  Secondary Succession: Old Field ~5 years after abandonment: perennial weeds dominate  Secondary Succession: Old Field ~15 years after abandonment: woody saplings establish  Secondary Succession: Old Field ~40 years after abandonment: large trees in canopy, shrubs/saplings in understory Larger, woody species have replaced saplings and herbaceous plant species  Secondary Succession: Old Field Left undisturbed, will support “climax community”  Climax Community: Traditionally “Final”, late stage of succession (“stable” community) Continues to change in “small” ways Remains “the same” through time if not disturbed  Climax Communities in Practice “Patchy” with multiple stages occurring at once Changes in unpredictable ways Disturbances are stochastic and dynamic disturbances larger trees grasses smaller trees shrubs  Climax Communities in Practice “Patchy” with multiple stages occurring at once Changes in unpredictable ways Disturbances are stochastic and dynamic disturbances larger trees grasses smaller trees shrubs Case Study in Mendocino, CA 0-20 years since harvest 41-60 years since harvest 81-100 years since harvest  Old Growth: “Climax” Community Large Gaps in the patches of canopy native plant communities Stochastic Events: Unpredictable, random Succession can be defined as the species composition in communities: A. at one given place in time B. as they change over time C. that are only affected by abiotic disturbance D. that are only affected by biotic disturbance  Lecture 22: Succession & Disturbance - Defining succession - Types of succession - Types of species involved in succession - Classic examples of primary succession - Agents of change (e.g., disturbances)  Species Categories of Succession Pioneer Species Late-Successional Species (among first to colonize) (colonize after pioneers) Hardy, adapt easily Stable conditions Many, small seeds Fewer, larger seeds Short life cycle Longer life cycle Fast growth rate Slower growth rate Smaller size at maturity Larger size at maturity Wind pollinated/dispersal Animal pollinated Asexual life cycle Sexual life cycle Intolerant of shade Tolerant of shade Replaced by incoming Not replaced by species incoming species  Species Categories of Succession Pioneer Species: the first ones to colonize (e.g., lichen growing on rock in primary succession) Lichen: mutualism between algae + fungi  Lichen Mutualism Lichen: mutualism between algae + fungi Fungus à housing, nutrients, & water Algae à sugar & C from photosynthesis  Early Successional Species Examples Glacier Bay, AK Yellowstone Dryas genus: Fireweed genus: small seeds, young age at seeds germinate readily, first reproduction, short life wind dispersed, prolific seed span, nitrogen-fixing producer, reproduce vegetatively via rhizomes  Succession Mechanisms Succession may be linked in one of three processes: 1. Facilitate the colonization for subsequent species (most often occurring model) by making the habitat MORE suitable (e.g., fix nitrogen) 2. Inhibit the colonization for subsequent species by making the habitat LESS suitable (e.g., casts too much shade) 3. Tolerate the colonization of subsequent species but have NO IMPACT on their establishment  Facilitation Example Softwoods are often replaced over time by hardwoods during succession. Many softwood species prefer sunlight à establish quickly in open sites, harsh conditions. Hardwood species tolerate low light levels as seedlings à do not tolerate open, harsh sites. Softwood development facilitates the colonization of hardwoods in the understory (e.g., habitat becomes more suitable, shady).  Facilitation Example Softwoods (e.g., pines) are often replaced over time by hardwoods (e.g., oaks) during succession.  Facilitation and Nutrient Changes Nutrient availability (e.g., nitrogen) in soil influences species composition. In early primary succession, there is little organic matter and nitrogen (N limits primary production). As N in soil organic matter increases, primary production increases. N-fixing species (e.g., alder, Dryas) facilitate colonization by other species. Which of these is a feature of an EARLY successional species? A. Fewer seeds produced B. Slow growth rate C. Sexual life cycle D. Wind pollinated  Lecture 22: Succession & Disturbance - Defining succession - Types of succession - Types of species involved in succession - Classic examples of succession - Agents of change (e.g., disturbances)  Sand Dunes Succession (Cowles, 1899) Observed changes in dune ecology along the shores of Lake Michigan in Indiana over several seasons.  Sand Dunes Succession (Cowles, 1899) Noticed that the dunes moved steadily away from the shore and different types of plants grew in the sand dunes.  Sand Dunes Succession (Cowles, 1899) Dunes are among the least stable landforms on Earth; changes happen fast and plants must adapt quickly to new environments. Sand Dunes Succession (Cowles, 1899) Predict how communities change over time without actually waiting for the pattern to unfold (would have taken decades to centuries)… Primary Succession: Glacier Bay, Alaska Student of Cowles set up permanent plots (still used today). As time and distance from melting from increased, plant species richness and change in species composition ALSO increased. Glacial retreat at 0.4 km/year  Succession in Glacier Bay, Alaska Pioneers: lichen (mutualism) ~30 years: moss (hardy, low) Dryas fireweed (rhizomes) (N-fixing) ~50 years: alder ~100 years: (N-fixing) spruce (shade tolerant) As communities develop and grow, do you think competition becomes MORE or LESS important in shaping community structure? A. More B. Less  Summary of Succession Early in succession, facilitative interactions are often important drivers (physical conditions are more stressful). Later in succession, competitive interactions among and between species plays a more important role (resource use more stressful). As succession progresses, larger, slow-growing, and longer-lived species usually dominate. Succession is driven by many mechanisms, but throughout, disturbances are an important factor.  Lecture 22: Succession & Disturbance - Defining succession - Types of succession - Types of species involved in succession - Classic examples of succession - Agents of change (e.g., disturbances) Agents of Change: Stress and Disturbance During succession, interactions results in the replacement of one species with another. Stress: A factor that reduces the growth or reproduction of individuals (e.g., reduced nutrients, competition). Disturbance: A large event that injures or kills some individuals, creating opportunities for other individuals to invade. Agents of change can be abiotic or biotic.  Abiotic Disturbance Examples Hurricanes (Hurricane Fran, 1996) Volcanoes (Mount St. Helens, 1980) Fires (Yellowstone, 1988)  Biotic Disturbance Examples Insect infestations Bison grazing  Scale of Disturbance Small, frequent disturbances (e.g., tree windthrow), can open patches of resources for other individuals. A mosaic of disturbed patches can promote change in species diversity over time. Late successional ecosystems are NOT static!  Intermediate Disturbance Hypothesis At a local scales, species richness and diversity PEAK at intermediate: values of disturbance frequency (e.g., time elapsed since last disturbance) spatial extents of disturbance (e.g., severity)  Intermediate Disturbance Hypothesis Modified from Connell 1978 Intermediate Disturbance mixture of species coexist (max diversity) Small, Large, rare common little to no only most turnover resilient in species species diversity survive  Human Impacts on Disturbance Can INCREASE the frequency, magnitude, and intensity of disturbance (e.g., farming) à areas are… dominated by early successional species. depleted of biomass, soil organic matter, and nutrient pools. Can DECREASE the frequency, magnitude, and intensity of disturbance (e.g., fire suppression) à areas are… dominated by late successional species. more susceptible to catastrophic disturbance (e.g., recent fires in western U.S.). Human Impacts: Fire Suppression  Lecture 22: Succession & Disturbance - Defining succession - Types of succession - Types of species involved in succession - Classic examples of succession - Agents of change (e.g., disturbances)