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Prospects for a Broader Understanding of Ecosystem Function in the Mojave Desert Region

Prospects for a Broader Understanding of Ecosystem Function in the Mojave Desert Region. J. Mark Porter Rancho Santa Ana Botanic Garden Claremont Graduate University. Ecosystem Function and Diversity. Controversial hypotheses of relationship.

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Prospects for a Broader Understanding of Ecosystem Function in the Mojave Desert Region

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  1. Prospects for a Broader Understanding of Ecosystem Function in the Mojave Desert Region J. Mark Porter Rancho Santa Ana Botanic Garden Claremont Graduate University

  2. Ecosystem Function and Diversity • Controversial hypotheses of relationship. • Changes in biodiversity cause changes in ecosystem function. • Increased biodiversity produces greater ecological stability (MacArthur 1955; but see also Goodman 1975).

  3. Ecosystem Function and Diversity • Increased biodiversity is associated with increased ecosystem function.

  4. Ecosystem Function and Diversity • Increased biodiversity is associated with increasing but saturated ecosystem function (Diaz and Cabido 2001).

  5. Three Complications with Ecosystem Function and Diversity • How we measure ecosystem function. • How we measure diversity. • Overly simple model used to describe a very complex series of interactions (too reductionist).

  6. Measuring Ecosystem Function • Pathways of energy flow. • Carbon/nitrogen cycling. • Water cycling. • "…ecological and evolutionary processes, including gene flow, disturbance, …" (Noss 1990): the key to a broader understanding.

  7. Ecosystem Function and Reproductive Ecology • Examination of breeding systems and pollination biology are a direct assessment of niche parameters (ecosystem function). • Current knowledge is meager. • Example: Linanthus maculatus (Parish) Milliken, margin of the Mojave Desert.

  8. Linanthus (Gilia) maculatus • Diminutive annual. • Coachella, Morongo Valleys, Joshua Tree NP area. • Because of the miniscule flowers assumed to be self-compatible and autogamous (Patterson 1989, pers. comm.).

  9. Pollination biology • Corolla pigmentation with “nectar guides” but no nectar production. • Visited by minute beetles, Trichochorus (Melyridae).

  10. Breeding System • Cross-pollination studies, examination of pollen tube growth (LaDoux 2002). • Self pollen will not germinate on the stigma. • Outcrossed pollen germinates and grows to the ovule. • Linanthusmaculatus is apparently self-incompatible, requiring insect-mediated pollination.

  11. Linanthusmaculatus • Caged bird in a mine: a species that is most susceptible to loss of habitat and population reduction, indicating functional problems in an ecosystem. • Sporophytic SI requires high genetic diversity at SI-loci. • Loss of genetic diversity will result in reproductive failure.

  12. Measuring Ecosystem Function • Reproductive capacity and gene flow is perhaps the most important biotic function in ecosystems. • Genetic data can be used to express patterns of gene flow. • Example: three taxa from the Colorado Plateau.

  13. Pediocactus winkleri K.D. Heil • 15 populations, 12 individuals. • Sampling chloroplast haplotype diversity DNA sequencing of trnL intron, trnL-trnF intergenic spacer (ML analysis).

  14. Pediocactus winkleri • San Rafael Swell populations share a common origin. • There are substantial genetic differences. • Genetic topography does not correspond with named species.

  15. Astragalusdesperatus M.E. Jones • 18 populations; 25 individuals. • Survey of 35 RAPD primer pairs. • UPGMA, Neighbor joining.

  16. Astragalus desperatus • San Rafael Swell populations are similar. • There is great genetic diversity within the Swell. • There is moderate correspondence with taxonomy.

  17. Hymenoxys (Tetraneuris) acaulis (Pursh.) Parker • 18 populations; 25 individuals. • Survey of 30 RAPD primer pairs. • UPGMA, Neighbor joining.

  18. Hymenoxys acaulis • Pronounced genetic gradient associated with San Rafael Swell. • Remarkable genetic diversity within the Swell. • Genetically divergent populations are not taxonomically recognized.

  19. A different perspective on ecosystem function and biodiversity • Different plant species may possess similar patterns of genetic architecture. • This may also reflects dynamic processes within the ecosystem. • Addition of a temporal dimension can allow a direct assessment of genetic response to change in habitat or management.

  20. Measuring diversity • Species and subspecies counting • Based on taxonomy rather than biology • May represent an underestimate or overestimate of biodiversity • Functional groups • Groups of species with “similar niches” and represent functionally equivalent entities • Based on assumption rather than biology

  21. Measuring biodiversity by taxon counting • Taxon counting represents current understanding (or opinion) of diversity. • Example: Aliciella (Gilia) leptomeria group • Cronquist (1984) recognized 1 species with 2 varieties. • Day (2002) recognizes 5 species

  22. Maximum likelihood analysis of cp DNA trnL-F, 1240 bp. • -ln(L)= 3699.16693 • Aliciellialeptomeria complex: blue. • Cronquist: black and white. • Day: color.

  23. Aliciella leptomeria complex A. “subacaulis” A. humillima A. triodon A. micromeria

  24. Measuring biodiversity • Taxonomic perspectives influence measures of diversity. Historical taxonomies have underestimated diversity. • ML analysis provides evidence of at least 10 genetically unique lineages. • Cryptic biodiversity

  25. Measuring biodiversity • Need for greater analysis of biodiversity. • Focus on genetically cohesive units rather that taxonomic entities. • It is critical to develop a knowledge base of biodiversity. • This can best be accomplished by encouraging basic scientific research on public lands.

  26. Ecosystem Function and Biodiversity • Perhaps the greatest challenge in developing more appropriate models is the paucity of observational data. • Observational data provides the “biological reality” needed to refine models. • Needed sources of insight include reproductive biology, genetics and biodiversity studies at a landscape level.

  27. Ecosystem Function and Biodiversity • As important as the research, is access to the results and the data. • Web access can facilitate greater trans- disciplinary collaboration and meta-analysis. • There are currently several resources: • Desert Managers Group (www.dmg.gov) • Mojave Desert Ecosystem Program (www.mojavedata.gov)

  28. I’ll see your research online…

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