Biosphere 2

Exercise 5: Herbivory and Plant Diversity
Module 5: Community Ecology: An Introduction to the Players and How to Measure Communities

Background Lecture

1. Instructor gives the biological background during the lecture on role of herbivores in the ecosystem, emphasizing the diversity of types of herbivory 
• Introduction to community ecology 
• Factors controlling community structure
• Interspecific competition
• Abiotic stressors
• Herbivory/predation
• Exotics - invasion
• Focus on:  Role of herbivory in structuring plant and animal communities. 
• Brief mention of coevolution and the chemical arms race between insect herbivores and their host plants 
• Background history of grazing in the West and effects on plant and animal communities
• Review ways to report  community diversity:
• Species richness
• Diversity indices
2. Students will be given background information on the recent grazing use at B2 and vicinity.
• from interview with B2 Ranch manager 
3. Students will be asked at the end of the lecture to begin thinking of how to experimentally answer the question: "What is the effect of grazing on plant diversity and abundance?" 

Independent and dependent variables

1. Independent variable in the experiment is level of grazing, this season. 
• Most other abiotic forces will be factored out because the experimental plots are immediately adjacent.  In 2000 plots, hillslope position was one factor varied with fenced study areas. This affected drainage and slope angle to some extent.  Also, ungrazed areas between road and fences were subject to enhanced runoff from road.
• Students need to sample randomly about the plot to minimize sampling biases.
• Students will need to measure dependent variables that best summarize the successional status of the plot and the effects of grazing.  
2. Dependent variables of the plants in their plots that they could use in their experimental design, not all of which are of equal utility in answering the question — several do not summarize the status of the plants within the experimental plots but are still describe aspects of the plots 
• Plant diversity of woody plants - trees and shrubs
• Plant diversity of cacti and herbaceous layers
• Plant abundance
• Plant cover (include bare ground cover)
• Average plant height (for shrubs, grasses, and forbs)
• Others? 

Preparation tasks

1. Check with B2 Ranch manager (Harold Herly, in 2000) for ok to use B2 range for class.
2. Also ask manager for this season's grazing use levels and which plots not currently occupied with cattle (!)

Implementation

1. After lecture, before the start of field time, the students will be asked to confer with their labmates and will be required to draw up a plan outlining the experimental design of their group 
• The best design will be determined by consensus and will be used for the entire class 
• This will allow for pooling of the data and enhanced statistical power 
• Students should also determine the necessary list of materials and provide the list to the instructor — the instructor will determine whether there are sufficient materials to address the experimental design 
2. Possible methodology 
• Select areas for sampling with different levels of grazing.  These will include both fenced grazed areas and ungrazed roadside areas outside of fencing.  
In 2000 —
• Study areas were just west and south of the main (first) security gate.  Three areas were selected:  (1) heavily grazed to the SE of the road, (2) moderately grazed, to the NW of the road, behind the fence, and (3) ungrazed, between the road and fencing for (2).  The ungrazed plot actually showed signs of very light grazing — by other herbivores?  The moderately grazed area had had ~65 head for ~4 months, just rotated off 2-3 prior to exercise (8/2/00).
• On the ridge NW of these areas is a watertank, that looked to be heavily impacted within the moderate grazed area.
• Within each of the study areas, students lay out line intercept transects (e.g., 50 m) and record:
• species presence.  Bag and label cuttings of unknown spp.
• cover, including bare ground.  Include plant overlaps.
• plant height, except for overstory trees (Mesquite)
• At randomly selected locations along each line (use a random number table), harvest all grass+forb biomass within a plot frame (0.5x0.5m?).  Collect in baggies.  Weigh in lab (account for tar wt). 
• Enter GPS and other eBiome data into DataLogger
• Enter line intercept and biomass data into Excel.
• Calculate species richness and alpha diversity.
• Calculate relative and absolute cover. 
• Do statistical analyses (chi-square on species diversities; t-test on continuous quantitative data = cover, height, biomass).  Analyze were appropriate by canopy classes = grass+forb, cacti, shrubs, trees) 
• Plot out data on Excel using graphing function 
• Present the work as an oral report at the end of the day, presenting hypotheses, methods, results (referring to the illustrations and statistical tests they performed), and conclusions.

Rev 4/21/01