05 measuring species richness

Slide 1: 

Measuring species diversity Species diversity considers both the number of species and their relative abundances: species richness = # of species species evenness = relative abundance

Slide 2: 

Both forests have 5 species. Which one is more diverse?

Slide 3: 

Calculating Index of Species Diversity Shannon Index (H’) H’ = -  pi x ln(pi) pi = proportion of ith species s = # species in community H’ = 0 in community with single species H’ = large with species richness and evenness increasing

Slide 4: 

Calculate H’ for each community H’ = 0.7 H’ = 1.6 Community A Community B

Slide 5: 

Rank Abundance Curves X-axis is rank in abundance vs. Y-axis is relative or proportional abundance (log-scale) What does it look like for community A and B?

Slide 6: 

Differences in species richness shown by differences in where line ends up (x intercept) Differences in species evenness shown by slope of line

Sampling Plant Abundance & Relative Abundance : 

Sampling Plant Abundance & Relative Abundance How does one determine plant abundance in a complex vegetation matrix? Need an accurate, but simple and replicable method to estimate species-specific abundances. Several methods exist, each with strengths and weaknesses SO – need to know what your goals are before choosing a method.

Basic Issues in Estimating Plant Abundance : 

Basic Issues in Estimating Plant Abundance What is the sample unit? Define in advance, with good reasons related to your question Sample should be random or stratified random Why? What are the implications of random sampling What technique (of many) should be used to estimate plant abundance? How many replicates are needed to get a good estimate? Need to know your plants for species-level IDs

Different Estimates of Abundance : 

Different Estimates of Abundance Frequency: quantitative expression of presence or absence of individuals of a species in sample unit Canopy cover: % of the ground covered by a vertical projection of the outermost perimeter; small openings within canopy are included Density: Number of individuals or stems per unit area (does not equate to cover measurement) Production: Total biomass in sample unit Basal Cover: cross-sectional area of stems of plants – different than canopy cover

Frequency : 

Frequency Easiest and fastest of methods Describes how common a species is and how it is distributed over space Highly influenced by size & shape of quadrats used

Canopy Cover : 

Canopy Cover Important vegetation & hydrologic characteristic Usually expressed as a %, but can be made absolute (m2/ha) Repeatability can be iffy when multiple individuals are gathering data.

Density : 

Density Useful when need absolute counts of individuals/ unit area Problems arise if comparing plants with different life forms and size May be difficult to identify individuals, but stem density can be useful nonetheless

Daubenmire Method : 

Daubenmire Method Place 20 x 50cm frame over randomly selected locations along transect in systematic way Estimate cover data by species using cover class category 6 different cover classes – note marks on frame Repeat estimates with a series of replicates Calculate average cover estimate using mid-point value for each category 5% 25%

Line Transect Method : 

Line Transect Method Very reliable method unless vegetation dense Horizontal, linear measurements of plant intercepts along the course of a line (tape) Lines of 15-30m are recommended with replicate transects Best for foliar and basal cover and composition by cover Best suited for semiarid bunchgrass-shrub vegetation Line

How can we estimate the amount of salt in soil? : 

How can we estimate the amount of salt in soil? We can measure the electrical conductivity of a soil Measures how well a solution conducts electricity Units of Siemens per meter (S/m) or dS/m Related to the total cations (Ca2+, Mg2+, K+, Na+, H+) and anions (NO3-, SO42-, Cl-, HCO3-, CO32-, OH-) that are soluble in the soil High soil conductivity values indicate a saline soil Salt concentration can be estimated mg/L salt = 640 x EC (dS/m) Generally prepare a 1:1 soil:water mixture (by mass) and then measure conductivity using a conductivity meter 0 - 1.2 dS/m  nonsaline 1.2 – 2.5 dS/m  slightly saline 2.5 – 4.8 dS/m  moderately saline 4.8 - 9.0 dS/m  strongly saline > 9.0 dS/m  very saline