Species abundance and diversity (Ch. 16)

New Unit: Communities/Ecosystems Community: Interacting species in defined area. Functional groups: subdivide organisms based on life history –Guild: Organisms living in same fashion Animal Ex.: granivore guild Harvester ants K-rat

New Unit: Communities/Ecosystems Growth form: Combination structure + growth pattern. Ex.: tree, shrub, graminoid, forb, climber

Species Abundance How express? Log abundance (x-axis), number species in abundance category (y-axis) –Ex, plant species (% cover measures abundance) –Ex, bird species (counts measure abundance) Curve?

Species Abundance Normal (bell-shaped) curve –x-axis log scale: lognormal distributions

Species Abundance Often only part curve seen. –Why? Sample size. Ex, moth community & sample size Tiger moth (Arctiidae) Sphingid moth (Sphingidae)

Species Diversity Two factors: –1) Species Richness Number species

Species Diversity Two factors: –2) Species Evenness Relative abundance of species

Species Diversity How integrate? Diversity Index. Gives single number

Species Diversity Common: Shannon Wiener Index –Fish diversity lab! Ecology SU 2005

Species Diversity Shannon Wiener Index: s H´ = -  p i log e p i i=l H ´ = Value of index p i = Proportion individuals of i th species log e = Natural log S= Number species in community

Species Diversity Ex: b greater diversity (same richness)

Rank Abundance Curves Rank abundance curves: –Relative abundance (proportional abundance: y-axis, log scale) vs. abundance rank (x-axis) a vs. b

Rank Abundance Curves Ex: reef fish communities (Gulf of California)

Rank Abundance Curves Which more diverse? (Richness, evenness)

Environmental Complexity In general: diversity increases with environmental complexity (heterogeneity) Ex, warblers (eat insects on trees) Environmental complexity = foliage volume

Environmental Complexity Foliage height diversity correlates positively bird species diversity

Environmental Complexity Hutchinson (1961): –Phytoplankton: simple environments, compete same nutrients –But many species coexist

Environmental Complexity Algal niches. –Ex, Diatoms (Protists, Phylum Bacillariophyta) –Photosynthetic –Cell walls: silicate

Environmental Complexity Coexistence depends on ratio silicate:phosphate Different niches: different diatoms dominate

Environmental Complexity Do nutrients vary in “real world?” Ex, Pyramid Lake, Nevada

Environmental Complexity Ex, Pyramid Lake, Nevada

Environmental Complexity Tropical rain forest diversity? Amazon: 1 hectare (2.47 acres) up to 750 tree species USA has 850 native tree species!

Environmental Complexity Diversity due to: –1) many species per community –2) many communities per unit area Complexity helps explain diversity

Environmental Complexity Relationship nutrients and rainforest richness? –Negative! –Competitive exclusion by best competitors

Environmental Complexity Reducing environmental complexity –When humans add nutrients (intentionally or not!) Reduces diversity –Reduces limiting nutrients

Environmental Complexity Ex, English grassland fertilized since 1856!

Environmental Complexity Ex, N fertilization & ectomycorrhizal fungi diversity –N aerial pollutant (Alaska factory)

Environmental Complexity Contributes to diversity But so does…disturbance Define??

Disturbance and Diversity Disturbance: departure from “average?” Sousa: –Discrete, punctuated, killing, displacement, or damaging of individuals that directly or indirectly creates an opportunity for new individuals to establish. White and Pickett: –Relatively discrete event that disrupts ecosystem, community, or population structure and changes resources, substrate availability, or physical environment.

Disturbance and Diversity Two major characteristics: –Frequency (how often) –Intensity (how severe) Abiotic: fire, hurricanes, ice storms, flash floods Biotic: disease, predation, humans

Intermediate Disturbance Hypothesis

Intermediate Disturbance Ex: intertidal zone –Disturbance depends on boulder size.

Intermediate Disturbance Richness greater medium boulders

Temperate Grasslands American prairie dog disturbance….

Disturbance

Prairie dog control: reduced populations 98%

Humans as disturbance Human disturbance & diversity –Ex, chalk grasslands (Europe) –Graze livestock, cut hay –What happened when “protected”?

Humans as a disturbance Diversity dropped (Brachypodium dominated)