Community effects on ecosystem processes CMM Chap. 12 I. Introduction A. The context – 1. ClORPT 2. Loss of biodiversity 3. Species invasions B. What is biodiversity? C. What is ecosystem functioning? II. Organism effects on ecosystem processes A. Community determinants B. Functional determinants: interactive controls III. Effects of diversity on ecosystem processes A. Magnitudes of processes B. Stability of processes C. Synthesis Powerpoint modified from Chapin (http://www.faculty.uaf.edu/fffsc/)

A.1. State factors and interactive controls: Species effects on interactive controls determine ecosystem consequences 1.3 How will changing biodiversity affect ecosystem functioning?

2. The context: altered biodiversity Chapin et al. 2000

2a. Loss of Global Biodiveristy: Current extinction rates are 10-100 fold higher than past - Extinction rates ~100-1000 fold greater than background - Caused by human activities - What are the ecosystem consequences? 100 well-documented extinctions in last 100 years of birds, mammals and amphibians Examples: great auks, passenger pigeons, numerous birds on guam (brown tree snake), others? Which? Where? IUCN red list has 784 documented extinctions since 1500. 12.1

The “Sixth Extinction”? 2. Devonian 370 mya 5. Cretaceous 65 mya 1. Ordovician 440 mya 4. Triassic 210 mya The scale of the current extinctions is on par with known extinctions from the geological record, of which there have been 5. Most famous: end of the cretaceous when dinosaurs went extinct probably because of an asteroid impact. Biggest was the Permian extinction about 230 mya, when ~50% of families of taxa disappeared. Not known why. 3. Permian 250 mya National Geographic 1999

2b. Loss of Regional Biodiveristy: Problems can occur long before species go extinct. - Local or regional extinction (extirpation) can be just as important and maybe more important than global extinctions. It is certainly more common. - Complete species loss from a given area not required - Changes in relative abundance of native species can have large impacts, especially if changes involve a dominant species - Caused by human activities - What are the ecosystem consequences? © National Geographic Magazine 2007

3. Introductions of exotic species Washington examples (to name just a few): Cheatgrass (Bromus tectorum) (eastern WA) http://www.cabnr.unr.edu/CABNR/Newsletter/FullStory.aspx?StoryID=41 Biotic change of global proportions Local or regional “exotics”; e.g. Mountain Goats in the Olympics. Mountain goats are native to the Cascades but geologic evidence indicates they never occurred in the Olympics prior to introduction. Spartina alterniflora (cordgrass) in Gray’s Harbor European Green crab (Carcinus maenas) http://baycenter.wordpress.com/2007/10/17/43/ http://massbay.mit.edu/exoticspecies/exoticmaps/images/carcinus_big.jpg

Shifts in species can be difficult, expensive, or impossible to reverse. Changes in species can lead to new ecosystem states from which it is very difficult to change back – difficult, expensive, time consuming if at all. Costs: $138 billion/yr (1999 dollars) according to researchers at Cornell (OTA ~$1.1 billion/yr; NASA – 100-200billion/yr for monitoring, containment, eradication of invasive species (http://www.news.cornell.edu/releases/Jan99/species_costs.html) compared to cost of war in Iraq ~$420 billion over the last 4 years. (http://nationalpriorities.org/index.php?option=com_wrapper&Itemid=182) ~$9 billion/mo as estimated by Congressional Budget Office (CBO) = $108 billion/yr (http://usgovinfo.about.com/library/weekly/aairaqwarcost.htm) Reed canary grass, Whatcom County

Introductions Establishment Invasions Noxious pests Not all introduced species become problems in their new habitat, but those that do can cause extensive ecological and economic damage. Introductions Establishment Invasions Noxious pests

B.What is biodiversity? Genetic Species Functional groups Effect Response Community types Ecosystem arrangement on the landscape

Salmon - Genetic diversity maintains local adaptation Risk of extinction of Chinook stocks Individual stocks show a different picture, however. Ok in AK, but S parts of range is problematic on both continents Represents evolutionary potential http://www.pnl.gov/news/ Augerot 2005

Functional group diversity: Need to understand how responses link to effects on processes. Different response groups Suding et al. 2008

Understanding interactions Cows are good?! Bay checkerspot Invasive grasses Plantago erecta Need knowledge of biology – in this case grazing done in concert with conservation biologists assessing populations of the endangered Bay Checkerspot butterfly. L. Gonzalez photos 2005 D. Hooper photos 2005

Ecosystem distribution matters for some services Wetlands & riparian buffers: Flood control, Nutrient filtration Good, Bad and Beauty. Include student photos. http://extension.umd.edu/environment/index.cfm

C. What is ecosystem functioning? Ecosystem properties (non-qualitative) (production, nutrient cycling, energy flux, etc.) Ecosystem goods – (“Provisioning services”) directly marketable Ecosystem services – benefit human endeavor, but harder to quantify in economic terms Regulating: pollination, pest control, water purification, maintenance of soil fertility, climate regulation, etc.; Cultural: recreational, educational, spiritual, etc.

II. Organism effects on ecosystem processes A. Community context

Impact of organisms on ecosystems depends on: D. Species interactions What are keystone species?

B. Functional Effect Traits Species’ functional traits influence ecosystem properties via direct processing (2)(e.g., photosynthesis, trophic interactions) and by altering other interactive controls: 3a – limiting resources, 3b – disturbance regime, and 3c – “modulators” such as temperature. 3a: water; plants differ in rooting depths? Differences in water use efficiency influence water available for run-off and transfer of water from soil to atmos.? 3b. Species differ in flammability 3c. Moss cover in boreal forests insulate soil from warm summer air temp; keep soil temp low; cold anaerobic soils with reduced decomposition; enhance peat formation, tie up nutrients. influence permafrost? Effect and respons groups Chapin et al. 2000

Species effects are an important interactive control Affect most ecosystem processes

1. Species effects on resource supply: Invasion of exotic N fixer augments N cycling Myrica faya is a N-fixing exotic tree in Hawaii

Deep-rooted species access more resources Enhanced NPP Alters ecosystem structure and functioning Native perennial bunch grasses of Calif. Have been replaced either by European annual grasses or by deep-rooted Eucalyptus trees that can access more water and nutrients

Deep-rooted species access more water Augments water available to support NPP

Relative growth rate is key trait with strong ecosystem impacts Determines NPP Influences nutrient requirement and litter quality

Plant species differ predictably in litter quality High-resource-adapted leaves decompose quickly Enhance nutrient cycling rates

Species effects on nitrogen mineralization Associated with differences in litter quality Agrostis scabra (As) Agroyron repens Poa pratensis Schizachyrium scoparium Andropogon gerardii 12.5

2. Species effects on climate a. in tropical forests Climate changes predicted for the Amazon Basin if rain forests were replaced by pasture.

2. Species effects on climate b. in boreal forest

3. Species effects on disturbance a. Many animals are ecosystem engineers Soil disturbance (worms, gophers, ants) Landscape disturbance (beavers) Harvester ant mound http://www.cwp.mines.edu/~norm/Photos/CBAutumn04/images/Cement%20Creek%20Beaver%20Dam.jpg

3. Species effects on disturbance b. Plants influence disturbance Decrease: Stabilize soils (e.g., sand dunes) Increase: Fire probability

Linked response and effect? Species effects on succession

Boreal conifer forests are born to burn After fire are replaced by less flammable deciduous forests (effect and response functional groups differ)

Fire in California chaparral (effect and response groups the same) http://www.werc.usgs.gov/fire/ http://www.csulb.edu/depts/geography/jpegs/woodsfirefreq.jpg

Fire in Hawaiian woodlands (effects of invasive grasses) - Schizachrium scoparium is an invasive grass that both promotes fire and resprouts quickly after burning. - Effect and response groups are the same  positive feedback. - Native Hawaiian shrubs and trees are not adapted to frequent fire and are eliminated.

III. Effects of species diversity A. Magnitudes of processes Enhance efficiency of resource use Primary productivity Mechanisms B. Stability of ecosystem processes C. Synthesis

Efficiency of resource capture/retention - greater plant species richness led to lower pool sizes of available N - from greater plant uptake? 12.8 Hooper & Vitousek 1997

2. Responses of Primary Productivity to Changing Plant Diversity Tilman et al. 1996 Hector et al. 2001 A number of experiments debate about both pattern and mechanism particularly, degree of comp vs. sampling effect define yr) Hooper and Vitousek 1997 Figure from Inchausti 2001

3. Mechanisms of diversity effects Complementarity - niche differentiation that leads to greater overall resource use in more diverse communities. My initial results seemed to indicate that compositional effects outweighed complementarity effects in productivity and nutrient retention. But I wanted to revisit the question of complementarity in more depth, for a couple of reasons.

Complementarity in plants with strong functional differences (Gulmon et al. 1983) Rooting depth E L (Vandermeer 1990) Light interception First I had assigned functional groups based on strong differences among species in phenology, rooting depth and other traits that I would expect would lead to complementarity. Opportunities for complementarity among plants in terms of “feeding niches” seem fewer than perhaps for animals - all plants depend on water, light, CO2 and the same suite of mineral nutrients for growth. But can have spatial and temporal separation of maximum demand. Examples from intercropping and serpentine grassland. Also nitrogen type (NO3, NH4, DON) as seen in some Arctic tundra species.

3. Mechanisms of diversity effects Complementarity - niche differentiation that leads to greater overall resource use in more diverse communities. Sampling - statistical probability of choosing a highly productive species. My initial results seemed to indicate that compositional effects outweighed complementarity effects in productivity and nutrient retention. But I wanted to revisit the question of complementarity in more depth, for a couple of reasons.

Detecting complementarity Sampling for dominant Complementarity Tilman et al. 1997

NO comp. General trend Again significant diffs among SFG’s, P’s highest, E’s, N’s lowest. Important for understanding effects later. but note that not all mixtures have L’s, the most prod. monoculture

B. Stability of ecosystem properties 1. Different kinds of stability a. Resistance b. Resilience 2. Mechanisms of diversity effects a. Compensation 12.2 Species richness Process rate

Response variation in species leads to less variation in ecosystems Portfolio effect Too technical? Cottingham et al. 2001

Many species with a continuum of trait differences can lead to compensation. 12.9 There may be little compensation for species with very distinct functional roles (e.g., keystone species) 12.2

B.3. Experimental tests of diversity effects on stability of ecosystem properties Note experimental difficulties 12.10 What else could cause this pattern?

Microbial diversity decreases ecosystem variability Focus on “supporting” services That’s fine in a microcosm, what about in the real world? McGrady-Steed et al. 1997

Report Warns of ‘Global Collapse’ of Fishing By CORNELIA DEAN Published: November 2, 2006 (Worm et al. 2006 Science) Extinction Collapse A paper by Boris Worm and colleagues in the journal Science got a lot of press last fall If you extrapolate this line down, you get to all fisheries collapsed by about 2048 – assuming we keep doing just what we’re doing now. Inset shows how collapses correlate with species richness in various regions of the world. Note that this is correlation, not causation! One implication is that less diverse systems less resistant to the disturbance imposed by harvest, and therefore less able to provide food in the long term. SYMBOLS???

Correlated response and effect traits: large ecosystem change Land use change and pollinator loss: effects on pollination efficiency Different response groups Suding et al. 2008 (data from Larsen et al. 2005)

C. Synthesis of diversity effects Figure from Field 1996 One year/one site Zone accessible to intensive management + site to site variation + year to year variation + different successional stages Without knowledge of exact functional roles

Summary Differences in species functional traits can influence ecosystem properties (effect and response groups) Direct effects and effects on interactive controls (climate, disturbance, resource availability) Diversity effects Magnitudes of processes Stability of processes Understanding mechanisms needs critical evaluation of alternative hypotheses.