Community and Biodiversity Consequences of Drought. Tom Whitham

Transcription

1 Community and Biodiversity Consequences of Drought Tom Whitham Northern Arizona University & Merriam-Powell Center for Environmental Research Flagstaff, AZ USA

2 Pinyon mortality North side of the San Francisco Peaks, AZ Photo mosaic by Paul Heinrich taken December 2003

3 Key Questions 1. As the dominant plant suffer water stress and die during a record drought, how will the rest of the dependent community be affected? 2. Will all vegetation types be equally affected or is it just restricted to certain species like pinyon and ponderosa pine? 3. What are the management implications for preserving biodiversity?

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5 On Trees Growing Under Low Stress Mean Arthropod Abundance / Tree Mean Arthropod Richness / Tree Figure 0 1B: Overall Mean Arthopod Abundance Is Highest On Herbivores Trees Growing Predators Under Low Parasites Stress A A B B A A B B Herbivores Predators A A Parasites High Stress Low Stress B High Stress Low Stress B In an arthropod community of 266 species, species richness is 2 X higher and abundance is 12 X higher in low stress sites than high stress sites. Trotter et al. 2004

6 Figure 2: Canopy Arthropod Community Composition Differs Significantly Between Trees Growing In High and Low Stress Environments 0.6 Stress Changes Arthropod Communities 0.4 High Stress Sites Y Axis High Stress 1 High Stress 2 High Stress 3 Low Stress 1 Low Stress 2 Low Stress Low Stress Sites X Axis Trotter et al. 2004

7 Ectomycorrhizae on fine root of pinyon pine

8 Environmental Stress Shifts Ectomycorrhizal Community O'Neill Crater RFLPs R = P < Low Mortality Sites High Mortality Sites Low Mortal High Morta Swaty et al Ecology

9 May 23, 2003 Watering experiment conducted by Crescent Scudder to test for community release.

10 Mean Athropod on Non-watered Arthropod vs Abundance Watered Pinyons 40 p= Watered Control Mean Arthropod Richness on Non-watered vs Watered Pinyons Species Richness p=.031 Watered Pinyons Non-watered Pinyons Supplemental watering increases arthropod abundance and species richness Scudder unpub. data 0 Watered Control

11 Low Stress High Stress Plant stress affects arthropod and microbial communities differently.

12 Ring width expansion (mm) a Tree ring widths b b c d d Climatic stress negatively affects pinyon growth. 0.0 % Ectomycorrhizal Colonization Mycorrhizal abundance c b a a a Mycorrhizal mutualists increase with intermediate stress, but decline at high stress levels Low Tree Rank High Stress Level Swaty et al Ecology

13 Tree Rings Predict Arthropod Species Richness 30% Richness vs. Ave Species Richness per Tree Y Data Adrian Stone unpub. data Ave vs 30% Richness Plot 1 Regr X Data Average Tree Ring Width

14 Moth Resistant Pinyon These phenotypes are genetically based and have extended phenotypes that have community consequences. Susceptible Pinyon Photo by Tom Whitham

15 Moth Resistant Tree 3X More Lilkely to Die During 2002 Drought Than Moth Susceptible Trees % mortality Moth Resistant Pinyons Stulz et al. unpub. data Moth Susceptible Pinyons

16 The extended phenotypes of moth resistant and susceptible trees affect a diverse community of about 1000 species. Whitham et al Ecology

17 Drought impacts on dominant plants will negatively affect their dependent communities. Photos by Tom Whitham & Alicyn Gitlin

18 Mortality of dominant plants at 20 randomly selected sites for each species within a 80km radius of Flagstaff. Population mortality (%) P = < Trees like cottonwoods should be of special concern due to low coverage. Gitlin et al. unpub. data Landscape coverage (%) Juni. Pond. Asp. Cotton. Manz. Pin. Dominant plant species

19 Summary 1. Through its effects on community drivers (i.e., dominant and keystone species), drought negatively affects biodiversity. 2. Arthropod and mycorrhizal mutualist communities are negatively affected by extreme drought, but differ in their community responses at low stress levels. 3. Unexpected outcomes are likely (e.g., insect resistant trees are more likely to die). 4. Extreme drought is a bottleneck event that is also an evolutionary event.

20 Mistletoe (Phoradendron juniperinum) on One-Seed Juniper (Juniperus monosperma) As a two-way interaction, a classic example of a parasite-host interaction

21 Juniper and Mistletoe Share a Common Avian Seed Dispersal Agent

22 Stands with mistletoe support 2x more seed dispersing birds Stands with mistletoe have 4x more juniper seedlings van Ommeren & Whitham 2002 Oecologia

23 Scales associated with reversals Number of species Time Spatial scales Any mix of above

24 Interactions Increase With the Addition of Factors 100 % of Significant Interaction Terms Observed Total Observed Significant Interactions Observed Reversals Number of Statistical Factors (Species, Time, Space) # of Statistical Factors Bailey & Whitham 2003

25 Management & Research Issues 1. In the absence of long-term community-level studies, fundamental errors in interpretation are likely due to the high probability of reversals. Need to support such studies to minimize these errors. 2. Need to minimize human impacts that exacerbate the effects of drought. 3. Need special emphasis on rare habitat types that are especially sensitive to drought (e.g., riparian habitat and springs). 4. Marginal or edge habitats that suffer chronic stress can be barometers of change and may be crucial to preserve as sources of extreme genotypes that may be best adapted to changing environments. << FHM Working Group Agenda