esa 2014 a massive and a tiny herbivore species drive patterns of plant community structure and...

Download ESA 2014 A massive and a tiny herbivore species drive patterns of plant community structure and landscape heterogeneity

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My 2014 ESA talk on the role of termites and elephants in shaping plant communities and landscape heterogeneity. On one hand, termites and elephants change plant communities by themselves. Termites create mounds which have different soil, nutrients, and water availability. These mounds form separate plant "islands" that are home to distinct plant communities. Elephants, meanwhile, eat mostly trees and shrubs, and this diet can also change plant communities by reducing the numbers and abundance of certain plant species. Together, however, it appears that these two species also affect each other. Elephants reduce trees, which means there are fewer resources available for termites. As a result, termites form fewer mounds in areas where elephants are present. This changes landscape-scale patterns in plant communities.

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  • 1. A massive and a tiny herbivore species drivepatterns of plant community structure andlandscape heterogeneityGrace CharlesUC Davis

2. Linking ecological drivers andlandscape heterogeneity Landscape heterogeneity is a major driver andmaintainer of biodiversity Conversely, certain subsets of species(keystones) can actually create heterogeneity What drives the creation and maintenance oflandscape heterogeneity? Can keystonesinteract, and what are the consequences ofthese interactions? 3. Savanna ecosystems Cover around 20% of earths land surface Some of the last repositories of largemammalian fauna Community structure is highly heterogeneousand is heavily influenced by both biotic andabiotic drivers 4. Study siteSemi-arid, Acacia drepanolobiumwooded grassland Kari Veblen 5. Striking heterogeneity at the landscape scaleLow termite mound 6. KLEE Kenya Long-Term ExclosureMWO WCCMWC C W200mSix combinationsoflarge mammalianherbivoresC = Cattle allowedW = Wildlife allowedM = Mega-herbivores allowed(elephants and giraffes)ThreereplicateblocksExperiment 7. KLEE Kenya Long-Term ExclosureMWO WCCMWC C W200mSix combinationsoflarge mammalianherbivoresC = Cattle allowedW = Wildlife allowedM = Mega-herbivores allowed(elephants and giraffes)ThreereplicateblocksExperiment 8. A tale of two keystones1. Termites(Odontotermes spp.)Fungus growing, generalistherbivores/detritivores Forage for woody biomass,dung, even bone(!)(Freymann 2007)Mounds have high soil nutrients,water infiltration rates, differentsoil texture (less clay, more sandand silt)Herbaceous vegetation on, andsurrounding termite mounds isdistinctMounds are generally treeless 9. A tale of two keystonesTermite moundsHyperdispersed, highlyproductive mounds havecascading effects on theproductivity of surroundingbiotic communities (Pringle 2010) 10. A tale of two keystones2. ElephantsKnown to radicallyaffect landscapeheterogeneity throughreductions in woodystandsTree and shrubconsumption mightreduce resourceavailability to termites 11. Q1: Do termite mounds createheterogeneity in plant communities? H1: Plant communities on termite mounds aresignificantly distinct from those off termitemounds H2: Because both keystones forage for acommon resource, woody biomass, theremoval of megaherbivores should increasewoody biomass and, in turn, lead to anincrease in termite density 12. Do termite mounds createheterogeneity in plant communities? Censused plantcommunities on and offtermite mounds in KLEEexperimental plots(15/plot) Vegetation surveys:Presence/absence andpercent cover of all plantspecies within 1m2quadrats NMDS analysis of plantcommunities 13. Termites mounds support distinctplant communities PERMANOVAVegetation~ Microhabitat P = 0.001*** 14. Q2: Do megaherbivores influencetermite abundance? H1: Plant communities on termite mounds aresignificantly different than those off termitemounds H2: Because both keystones forage for acommon resource, woody biomass, theremoval of megaherbivores should increasewoody biomass and, in turn, lead to anincrease in termite density 15. Do megaherbivores influence termiteabundance? Methods 10m x 200m transects across all KLEE plot area(72,000m of transects in all) to determinetermite mound density and abovegroundtermite mound footprint in plots includingand excluding megaherbivores. Integration with previously collected KLEEdatasets on tree density/HA. 16. Do megaherbivores influence termiteabundance? Methods 10m x 200m transects across all KLEE plot area(72,000m of transects in all) to determinetermite mound density and abovegroundtermite mound footprint in plots includingand excluding megaherbivores. Integration with previously collected KLEEdatasets on tree density/HA. 17. Do megaherbivores influence termiteabundance? Methods 10m x 200m transects across all KLEE plot area(72,000m of transects in all) to determinetermite mound density and abovegroundtermite mound footprint in plots includingand excluding megaherbivores. Integration with previously collected KLEEdatasets on tree density/HA. 18. Megaherbivores allowed 19. Do megaherbivores influence termiteabundance?Tree density/ HATermite moundfootprint (m2) per plotMegaherbivore presence+ _ 20. Do megaherbivores influence termiteabundance?R2 = 0.780.56** -0.28**R2 = 0.310.84*** 21. Putting it all together Termites and megaherbivores interact inprofound ways that strongly affect plantcommunity structure and ecosystemheterogeneity Megaherbivores reduce tree density, andthis leads to a reduction in termite mounddensity and footprint Megaherbivores reduce the landscapeheterogeneity produced by termites byreducing termite mound area Extirpation of megaherbivores may haveprofound consequences for large-scalepatterns in community composition,community structure, and nutrient cycling-+ 22. Putting it all together Termites and megaherbivores interact inprofound ways that strongly affect plantcommunity structure and ecosystemheterogeneity Megaherbivores reduce tree density, andthis leads to a reduction in termite mounddensity and footprint Megaherbivores reduce the landscapeheterogeneity produced by termites byreducing termite mound area Extirpation of megaherbivores may haveprofound consequences for large-scalepatterns in community composition,community structure, and nutrient cycling 23. Next steps Exploring multiple scales of landscapeheterogeneity- how do we rectifycounteracting patterns in heterogeneity? How do biotic interactions impactbelowground communities and overallecosystem function? What are the effects of other large herbivoreson termite mounds and plant communities? Cattle also appear to have a strong effect ontermite mound density 24. Thanks!KLEE:Truman YoungKari VeblenCorinna RiginosDuncan KimuyuField assistance:Mathew NamoniJackson Ekadeli 25. Questions?

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