Functional indicators of ecosystem processes

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Functional indicators of ecosystem processes

• David HooperDept. of Biology, Western Washington
  University

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Overview

• 1. Introduction scope of this talk
• 2. Three questions
• What processes? (very broadly)
• What functional traits? (just as broadly)
• What indices of ecosystem condition? Examples?
• 3. Conclusions, questions, considerations, and
  caveats

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Introduction

• Objective To identify and develop a suite of
  habitat-based biodiversity standards that, if
  achieved, will sustain the complexity of habitat
  and natural species assemblages necessary to
  preserve ecological processes within the
  ecoregions of Canada.

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Phase I Identify Representative biodiversity
indicators
Step 1 Identify ecosystem types of interest
Step 2 Identify goals (key ecological processes)
and threats
Step 3 Identify functional elements or
biodiversity predictors associated with each
stressor (or process?)
Step 4 Establish protocol to select thresholds or
standards for biodiversity predictors.
(Population viability analysis, Scenarios)
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Questions

• What types of processes?
• - Processes maintaining habitat
• - Ecosystem processes/services
• 2. What functional characteristics of species are
  important?
• - Response and effect traits
• 3. What indices of ecosystem condition might be
  used?

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Questions

• 1. What types of processes?
• 2. What functional characteristics?
• 3. What indices of ecosystem condition?

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Process-based approach

• A. Processes maintaining diversity Threats
• 1. abiotic characteristics
• resource availability Nutrient loading
• disturbance regime Fire suppression
• climatic conditions Climate change
• 2. Biotic interactions
• keystones Overexploitation,
• habitat loss, invasives
• mutualisms Nutrient loading
• critical prey Habitat loss

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Process-based approach

• B. Processes affected by diversity
• 1. Ecosystem properties (nonqualitative)
• Productivity, nutrient cycling, hydrologic
  cycles
• 2. Processes influencing other species
• (feedbacks to composition)
• disturbance regime, resource availability,
  biotic interactions
• 3. Ecosystem services (qualitative)
• Pollination, Pest control, Soil fertility,
  Protection against erosion, Nutrient
  uptake/control

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Habitat-forming processes
A
A
A
Abiotic conditions
Species
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Questions

• 1. What types of processes?
• 2. What functional characteristics?
• 3. What indices of ecosystem condition?

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External (environmental filters) and internal
dynamics (assembly rules)
Narrow range of response traits, e.g., Díaz,
Walker et al.
Widen range of coexistence traits, e.g., Weiher
et al.
Loreau et al. 2001
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Response vs. Effect Traits

• What traits allow survival in a given
  environment? (response to abiotic conditions)
• What traits allow coexistence in a community?
• (species interactions traits)
• What traits affect ecosystem properties?
• (effect traits)
• Are these the same? Are they linked or
  independent?

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Biodiversity and ecosystem functioning The
context
Response traits
Effect traits
(Chapin et al. 2000)
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?
Community changes
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Example of linked traits

• Low nutrient environment

Low RGR, high CN, low biomass turnover
Slow decomposition
Low productivity
Slow mineralization
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Community changes
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Examples of unlinked traits

• Optimum temperature for growth, plant morphotype
  (herbaceous, evergreen shrub, deciduous shrub)
  (Chapin et al. 1996)
• Responses to elevated CO2, any plant functional
  classification (Körner 2000)
• Disease resistance and community dominance (e.g.,
  American Chestnut/chestnut blight)
• Regeneration niche and adult niche (e.g., Grubb
  1977, Grime 1979)

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Importance of functional diversity

• Presence of relevant/necessary effect functional
  groups
• Diversity of response traits within functional
  effect groups (or vice versa)
• Likely persistence of ecosystem properties in
  face of a variety of environmental changes.

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The point

• We need a better understanding of the
  relationships between traits that determine
• - response to environment
• - species interactions
• - effects on processes

Improved capability to predict the consequences
of changes in drivers for biodiversity, ecosystem
functioning, and ecosystem services, together
with improved measures of biodiversity, would aid
decision-making at all levels. Millenium
Ecosystem Assessment (2005)
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Questions

• 1. What types of processes?
• 2. What functional characteristics?
• 3. What indices of ecosystem condition?
• - Examples of approaches
• a. Surrogate and direct measures
• b. Functional traits/species composition
• c. Functional diversity vs. species diversity

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Linking communities to processesSurrogate
and/or direct measures (no species intermediates)

• Abiotic conditions/habitat characteristics -
  when direct species/population measures arent
  possible or necessary.

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b. Linking communities to processesFunctional
traits/community composition

• When there are clear links between species
  present and processes/conditions of interest.

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Index of Biological Integrity (IBI)

• Uses multiple indicator taxa correlated with
  changes in habitat condition.
• Commonly used to monitor streams (fish Eastern
  U.S., benthic macroinvertebrates Eastern
  Pacific NW U.S.).
• Terrestrial insect version under development
  (Kimberling et al. 2001, Karr Kimberling 2003)

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IBI Approach

• Select sites over a gradient of human impacts.
• Measure a variety of taxa select as indicators
  only those that show consistent change across
  gradient.
• Determine reference community from minimally
  impacted sites.
• Score indicator taxa from monitored sites
  relative to reference sites 5 within range of
  reference sites 3, 1 split range of disturbed
  sites.
• Sum scores across all taxa scale for ecosystem
  condition from 10-50 (for 10 taxa index) 46-50
  (exc) 38-44 (good) 28-36 (fair) 18-26 (poor)
  10-16 (very poor)

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Example Benthic-IBI in PNW Streams(Morley
Karr 2002)

• Table 1. The 10 metrics of the B-IBI
• Taxa richness and composition
• total taxa richness
• mayfly taxa richness
• stonefly taxa richness
• caddisfly taxa richness
• long-lived taxa richness
• Tolerance and intolerance
• intolerant taxa richness
• tolerant taxa ()

Feeding and other habits clinger taxa
richness predators () Other
dominance by top 3 taxa ()
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Morley Karr 2002
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Pros

• Calibrated to ecosystem condition (by design).
• Standardized methodology for monitoring.
• Biotic indicators of habitat condition often
  better than abiotic indicators alone (integrate
  chemical, physical, biotic conditions over time).

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Cons/Room for research

• Based on response traits not necessarily a
  direct link to ecosystem processes or services of
  interest (e.g., inverts ? salmon bearing?).

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Cons/Room for research

• 2. Not yet diagnostic no direct connection to
  specific stressors limits use for recommending
  remediation action.

Biological response
Direct and indirect stressors (driven by human
pop. and resource consumption)
Modified from Booth et al. 2004
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Cons/Room for research

• 4. How to use in a predictive/scenario-driven
  way?
• - Not yet linked to population/community models
  of indicator taxa.
• 5. Finding appropriate reference reaches
• 6. Sensitivity?

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c. Linking communities to processes Functional
diversity
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How to measure functional diversity?

• - Select process of interest.
• - Measure functional traits in species likely to
  influence that process.
• - Standardize scales/determine weighting
• - Calculate multidimensional ecological
  distances among species
• - Sum differences across species in a community
• - Test different components of functional
  diversity for effects on processes (if using
  candidate functional characteristics).

Walker et al. 1999, Petchey and Gaston 2002
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How to measure functional diversity?

• Which traits to use?
• - Petchey et al. (2004)
• N-fixation
• height, mature biomass, SLA (RGR), longevity,
  leaf litter quality
• Predict response of productivity to changing
  functional diversity in BioDEPTH

But is diversity of these traits most important
for ecosystem properties?
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Functional Diversity in River Monitoring (Bady et
al. 2005)

• Q. Does using functional diversity give better
  accuracy and more precision with less effort than
  trying to measure taxa richness?
• Use Raos Q as measure of FD.
• Assess functional traits for all taxa
• Calculate dissimilarity matrix among species for
  each trait
• Calculate functional diversity of a given
  community based on relative abundances of species
  and their trait dissimilarities.

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Invertebrate traits
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Invertebrate traits (continued)
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Functional group delineation
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Monitoring results
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Their conclusions
1. Greater accuracy with less effort with FD
(sample a greater proportion of the total
diversity) 2. Greater precision with FD
(replicates in space or time were more similar
than with taxa richness)
BUT no explicit link to ecosystem processes or
habitat conditions. How do we know that this FD
metric tells us what we need to know about the
state of this ecosystem? NEED either response or
effect link to know if their points are true!
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Conclusions, questions, considerations and caveats

• Distributions and linkages between effect and
  response traits are not well known except in a
  few cases.
• Once appropriate functional traits are
  identified, they need to be explicitly linked to
  relevant processes - or rather, to identify
  appropriate traits, relevant processes must be
  identified first.

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Conclusions, questions, and considerations

• 3. Multimetric indices (IBI)
• - useful response metrics
• - calibrated to ecosystem condition
• - may not give diagnostic or predictive
  capabilities or direct links to ecosystem
  processes/services.

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Conclusions, questions, and considerations

• 4. Tension between species conservation and focus
  on ecosystem processes/services

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Monitoring approaches where will
diversity/biotic measures work as indicators?

• Processes maintaining diversity
• Processes affected by diversity
• Yes? Pollination, pest control
• No? Soil fertility (soil food webs too complex)
• Erosion (likely buffer sizes, placement,
  landscape metrics rather than populations of
  particular species
• Circular? Wetland functions nutrient uptake,
  denitrification, species preservation

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Millenium Ecosystem Assessment 2005
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Diversity where and why?
Where parks preserves, managed landscapes
(fringes, habitat remnants), managed fields
(genetic diversity of crops, soil
biodiversity). Why protection of species
persistence of individual ESUs (species,
subspecies), habitat processes, protection of
ecosystem services
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How to measure functional diversity?

• Which traits to use?
• - Walker et al. 1999
• height, mature biomass, SLA (RGR), longevity,
  leaf litter quality
• predict response to grazing less common
  species that are functionally similar to lost
  species will maintain ecosystem properties
• -But predicting which species will persist
  depends not just on EFFECT traits, but on
  RESPONSE traits

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Example Benthic IBI in Streams(Morley Karr
2002)

• 1. Disturbance gradient

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Taxa, response patterns
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Reference reaches
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Monitoring examples