Richness, S = number of species

Diversity, H’ = - pi log2 pi

, diversity:

alpha diversity: the diversity of a site beta diversity: the change in species composition from place to place, or along environmental gradients (turnover)gamma diversity: the diversity of a region or landscape due to either or both and

Global biodiversity patterns and changes

S

i = 1

(Begon et al. 1996)

In sea, diversity increases to 6000 m, then decreases (Sanders et al. attribute to stability, then resource deprivation…)

Macan’s Filter: If a species isn’t present at a site, is it because of…

Dispersal (age, distance/isolation) ? yes, propagules haven’t arrived and established.no, propagules arrived, but populations don’t

persist… Behavior (specialization/heterogeneity) ?

yes, colonists avoid this habitat.no, colonists settle, but don’t persist…

Abiotic factors (stress, productivity, heterogeneity) ?yes, physico-chemical conditions outside tolerable

range.no, abiotic conditions sufficiently benign…

Biotic factors (productivity, disturbance, heterogeneity) ?

yes: predators, pathogens, parasites, competitors or lack of mutualists exclude species.

no…

Interactions…

Stanley 1976 hypothesis: breakthrough that ended the Pre-Cambrian was the invention of ‘jaws’—the first herbivorous protists grazed holes in algal monocultures, producing environmental heterogeneity…

Are niches narrower (species more specialized) in the tropics (a)?

Can more niche overlap be tolerated without competitive exclusion (b)?

Are resource axes longer in the tropics?

Is niche space more completely filled?

Tropical vs temperate niches

England

Papua New Guinea

New Mexico

Lawton-Empty niches?

Bracken fern

Milankovitch theory: orbital oscillations of Earth cause cyclical changes in temperature and precipitation:

Eccentricity of orbit: 100 ky cycleAnnual timing of aphelion (point in planet’s orbit when

it is furthest from the sun) relative to summer solstice: 23 ky cycle

Tilt of wobbling pole: 41 ky cycle

Ruddiman 2000Dynesius and Jansson 2000

Orbitally forced species range dynamics (Dynesius and Jansson 2000)

• Mean duration of species 1-30 my, so species have endured many Milankovitch oscillations

• Oscillations more severe at higher latitudes than around equator, selecting in temperate, boreal and arctic species for– More vagility– Less specialization

Range restricted = < 50,000 sq. km

Dynesius and Jansson 2000

Larger effect (temperature change) at higher latitudes than near equator

Brown and Maurer 1989: Hypoth: N. Am. species with small geographic ranges are limited by local environmental conditions so should run NW, while species with large ranges limited by large scale patterns of vegetational or climatic zones that correspond to latitudinal bands (run EW)

North American reptiles Europe—small ranges should run EW

Diversity vs Productivity: a hump-shaped relationship, like intermediate disturbance?

Science 293 p. 625 (2001)

Longest running ecological experiment: 1843 - present

Parmesan, C. 1996Censused Edith’s checkerspot butterfly throughout its range for 151 previously located populations. Striking latitudinal trends in extinction: populations in Mexico 4x more likely to have gone extinct than those in Canada. Habitat loss was similar at southern and northern ends of range, suggesting range contraction due to climate change. This hypothesis also supported by less frequent extinctions at higher elevations.

Light triangles: extinctDark triangles: extant

Ice age 25-25 K y bp

SF Chronicle Nov 28 2003

Invasive species…

Over a wide range of pH in acidification experiments, and of nutrient concentrations in eutrophication experiments, ecosystem respiration and photosynthesis stayed fairly constant, while species composition varied markedly.

David Schindler whole lake manipulations in Experimental Lakes Region of southern Ontario

Schindler et al. 1985

Tilman and Downing 1994

Cedar Creek LTER

Dro

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ance

(bio

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1988/b

iom

ass

19

86)

Plots with higher plant diversity maintained more constant biomass across severe 1987 drought

Duffy et al. 2003: more diverse grazer assemblage more effective in removing algal epiphytes from sea grass beds

Ecosystem consequences of diversity loss…

(Chapin et al. 2000).• “Rivet hypothesis” (Ehrlich): which species are crucial to ‘holding

the wings on the plane’, esp. in changing environments?• Grasslands: less productivity, resilience after drought• Plant production enhanced linearly by mycorrhizal species

richness• Consortia of diverse microbes each contribute different enzymes

to speed organic matter decomposition and nutrient recycling• Societal costs of diversity loss (some speculative examples…)

– Passenger pigeons may have suppressed deer mice by competing for acorns, reducing Lyme disease reservoirs (Ostfeld)

– Cheatgrass fires reduce rangeland value and air quality (D’Antonio)– Teosinte, wild relative of corn, needed periodically to develop virus-

resistant strains—nearly lost to land conversion around Jalisco, MX, and now possibly subject to genetic engineering introgression (Chapela)

Moritz et al. 2000:Higher species diversity in tropical rainforest vertebrates because of higher rates of speciation, or lower rates of extinction?

Most sister taxa arose before Pleistocene, but recent species occur in heterogeneous, geologically or climatically unstable areas

Evidence for both gradient and allopatric diversification

Conservation strategies need to preserve both the important genetic lineages (variation) and the ecological processes that generate species (e.g. refuges and barriers: edges and forest core)