GENERAL LAB INTRODUCTION

Communities are constantly changing.  Organisms die and new ones are born to take their places.  Nutrients cycle within communities as energy passes through them.  The process by which communities develop is called succession, or ecosystem development.  The end point of the successional process is a climax community in which species diversity and composition are in some quasi-equilibrium and in which whole ecosystem production is nearly matched by whole system respiration.  The community is at its maximum biomass at this point.  And it will remain at this state until disturbed.  An ecological disturbance is broadly defined as an event that removes biomass from a system (e.g. a timber harvest, a fire, a lightning strike in a forest, etc.).  Disturbances may be very localized or cover large areas.  Disturbances vary greatly in their frequency of occurrence and intensity.  Both factors determine how “hard hit” a community will be by a particular disturbance.  The effect of disturbance is to [relatively] instantaneously move the community to an earlier successional stage.  From there, the community again develops via the processes of succession and ecosystem development.

The process of succession or ecosystem development is orderly and relatively predictable.  It begins with pioneer species or colonizing species that are fast-growing, short-lived, and prolific (we often call them “weeds”!).  These species are steadily replaced by longer-lived and slower growing species as more and more biotic structure is added to the community.  One very important characteristic of succession and ecosystem development is that, in the process, the community actually modifies its local environment.  Soil is an excellent example of something that is a product of a community developing from nothing.  There are numerous other examples of ways that communities actually “tailor” their local environment as they develop.

Succession follows two primary routes:  Primary succession is when a community “starts from scratch”, on new habitat.  Nothing precedes the community—not even soil.  The best examples of this are lava flows, where the community literally begins with nothing but the cooled volcanic rock.  Most communities develop along a secondary succession route, however.   This involves a disturbance that merely “resets” a community’s succession clock to an earlier time.  Some biomass is removed, but the community does not start over completely.  As an example, a clear-cut or fire that removes all of the trees and shrubs from an area of forest will probably not remove all of the soil (unless erosion completely decimates the area afterwards).  That soil contains organic matter, nutrients, and seeds that will help fuel the redevelopment process.  The community is thus not starting over from scratch.

The process of community succession was one of the first ecological concepts.  It came from observations by the phytosociological scientists of the late 19^th century.  By the turn of the century, the search was on for processes that explained differences in plant species distributions and dynamic change was considered.  From this came the idea we know today as succession.  Some classic early successional research was done in sand dune habitats along the southern shore of Lake Michigan and on coastal barrier islands.  The former studies involved plant species distributions and succession in a dune habitat where wind movement of sand is the key disturbance element.  In barrier island settings, it is the ocean (with its tides, salt, and salt spray) that is the key disturbance element.

Today, we will take a trip to Crandon Park on Key Biscayne (our model of a barrier island) to study community succession in the dune systems there. You will be using 1.0 m² quadrats to sample along transects that you will set from the high tide line to the uplands.  You will need a tape measure and a way to identify random points along your transect to sample (the point-intercept method).  From the transects sampled by your entire lab, you will use the diversity indices from last week to investigate plant species diversity vs. distance from the ocean.

PRE-FIELD LAB INSTRUCTIONS

1.  Generate several testable hypotheses as a class that you can test with today’s exercise.  Think about the source of disturbance in your system.

2.  Set up field data sheets for today’s work, remembering the importance of noting total numbers of all species in each quadrat and thus the importance of keeping track of all plant species you find.

3.      Divide into groups and work as teams in the field.  Work should be divided up so that all team members get to experience each aspect of the exercise.  In other words, don’t make one person record data for the entire lab exercise!

4.      Be sure that you have all field sampling equipment that you will need.  Read below and make a list before you leave the lab.

5.      All field teams should participate in sampling at least 2 transects, with a minimum of 10-12 quadrats per transect.  After sampling, return to the lab and your TA will pool transect data from all teams to generate larger datasets for each habitat.

FIELD LAB INSTRUCTIONS

1.      Lay out your transect first, noting that it may have to be longer than your measuring tape to cover the necessary gradient. Your group should then identify 10-12 random points to sample along your transect.  In each 1 m² quadrat, first identify all species present in the quadrat.  Then count and note the number of individuals of each species present.  Be sure to note where along your transect each quadrat was located.

2.      Sample as many transects as you can, but at least two.

3.      When you return to the lab, your TA will pool data from all transects sampled. 

Answer/address all of the following questions on your own paper.  In some cases, this will require computer printouts of spreadsheets, graphics, or statistical output.

1.       Present a clear list of the hypotheses that you tested in your species diversity  After each, briefly detail how you tested this question.

2.      What were the diversity indices for the two campus communities that you studied?  (Be sure to show your raw data and calculations)  Which had higher species diversity?  Why?

3.      Were your calculated values for Shannon-Weaver and Simpson’s indices the same?  If not, why not?

4.      What is the primary source of disturbance in the barrier beach dune system you studied in the succession lab?  What ways does this disturbance act to reduce biomass in your dune system?

5.      What relationship between species diversity and ocean-uplands gradient do you expect to see along your transects?  Do your data support this hypothesis?

6.      What did you notice about differences in gross morphological adaptations by the plants along your disturbance gradient?  How do these adaptations relate to your answer to question #4?

7.      Can you come up with any kind of zonation along your disturbance gradient?  What demarcations did you use to identify this zonation?