Nature: a harmonious & peaceful place?! What disturbs the peace?

Nature: a harmonious & peaceful place?! What disturbs the peace?

Disturbance Disturbance: a relatively discrete event in time that causes abrupt change in ecosystem, community, or population structure, and changes resource availability, substrate availability, or the physical environment Cause, Frequency, Severity, Size/Dispersion

Examples of disturbance in nature Glaciation the Little Ice Age ca. 1300-1750 Norway 2500km2 of glacier but retreating

Examples of disturbance in nature Feb 1, 2014. Mount Sinabung, Jakarta, Indonesia

Examples of disturbance in nature Fraser River Flood 1948

Examples of disturbance in nature avalanches

Examples of disturbance in nature Wave action in the intertidal

Examples of disturbance in nature

Examples of disturbance in nature Bioturbation

Examples of disturbance in nature Herbivory natural or anthropogenic is a common disturbance

Disturbance and. Disturbance: an abrupt change in the ecosytem, community or population structure and resource availability, substrate availability, or the physical environment Succession: directional change in community composition or structure over time following a disturbance

Succession of ecological communities Change in species composition over time progresses from pioneer species to climax community the sequence can be predictable Primary succession after catastrophic disturbance in newly formed habitats (no plants or organic soil) Secondary succession after disturbances that remove plants but soil & nutrients remain (moves away from climax)

Primary vs. Secondary Succession (regeneration) Which proceeds faster??

Classic old field succession What is the disturbance? What kind of succession is this?

Studying succession 15 Direct Measures: - Collect data at regular intervals following disturbance

Succession in Poland! oak-hornbeam forest 0 yr 7 yr 15 yr 30 yr 95 yr 150 yr

Studying succession 17 Direct Measures: - Collect data at regular intervals following disturbance - Experimentally induce disturbance or create new habitat and monitor species colonization

Direct Measures: Example: Intertidal primary succession on new habitat 18 Sousa et al. 1979

Studying succession 19 Direct Measures: - Collect data at regular intervals following disturbance - Experimentally induce disturbance or create new habitat and monitor species colonization Indirect Measures: Chronosequences: compare communities in same location with different start times

Succession on sand dunes

Lake Michigan, sand dune succession Lake What type of succession is this?

Succession of ecological communities Pioneer species adapted/able to survive as first colonists *often facilitate colonization by additional species Climax community final group of species the end point of succession assumed to be stable... until the next disturbance *often inhibit colonization by additional species sensu Frederic Clements 1916

Facilitation by pioneer species (alder) *N-fixing plant (via symbiosis with a filamentous bacterium)

Krakatoa Island, Indonesia 1883 What kind of succession is this? Why might animal dispersed plants arrive later?

Characteristics of early vs. late successional plants dispersal, rapid growth, early reproduction high competitive ability Which is more likely to have rapid population growth rates?

Experiment: Survival of seeds after 3 months of shade Which are more likely to be late successional species? Inhibition through shade tolerance * Smaller seeds suffered higher mortality

Case Study. Eruption of Mt. St. Helens May 18, 1980 27

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Conditions Post-eruption inorganic substrates (rock, ash) low soil moisture (drought) high erosion (shifting surfaces) high sunlight (no shading) high availability of space no organic nutrients Stress high Competition - low 30

What might limit succession in this new environment? - Dispersal - Inhospitable conditions What are the traits of the first plants to come back?? - Good dispersers - small seeds = longer dispersal distances - Ability to withstand harsh conditions - large seeds = better germination success

Facilitation by lupine Wind shade 32 C+Soil moisture + N (via nitrogen fixing bacteria in root nodules)

Facilitation by gophers Pocket gophers survived underground Mixed underlying soil with ash! Facilitation = a Biological legacy Allen and MacMahon 1988

Facilitation by other animals

" Succession on Mt. St. Helens Home Contact

Summary so far Disturbances can be described by cause, frequency, severity and scale Primary and Secondary Succession can be studied directly and indirectly using chronosequences Pioneer species may facilitate colonization by other species Climax species may inhibit further colonization Pioneer and Climax species have different life-history traits

Succession in intertidal communities (Fig 19.12- text) Expt 1. community change after rocks are scraped bare Start expt 2 Expt 2. rocks were scarped bare of algae and received one of five treatments Both barnacles present Identify the pioneer and climax species, describe the interaction between the algae and the two barnacles

What limits succession in Glacier Bay? Dispersal or inhospitable conditions 1 2 3 4 Experimental plantings of spruce seeds Observational data 1 2 3 4

Climax communities: the final stage? Succession in Douglas fir forest clearcuts Phases Establishment/initiation Competitive exclusion Maturation/diversification Dynamic climax 39 How often do ecosystems reach the climax stage? How do you know it is a climax community?

Fire as an organizing disturbance (fire maintained climax community)

Grazing and fire as disturbances Invasive cheatgrass a fire maintained climax community?

Disturbance Succession Disturbance and Diversity 42 frequent disturbance High Low

Disturbance Succession Disturbance and Diversity 43 Intermediate disturbance High Low

Disturbance Succession Disturbance and Diversity 44 Infrequent disturbance High Low INTERMEDIATE DISTURBANCE HYPOTHESIS Species diversity is highest when disturbance is intermediate

Summary

Summary Disturbances vary in cause, severity, frequency and size Primary and secondary succession are the somewhat predictable changes in community composition following a disturbance Succession proceeds from a pioneer community to a climax community Disturbances can reset the successional clock Diversity may be higher at intermediate levels