Community Ecology - Diversity-Productivity Relationships

Community Ecology
Diversity-productivity relationships

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Outline:

1. What is productivity, anyway?

A. Surrogates: rainfall, PET, biomass, veg height

2. Types of diversity-productivity relationships

A. Positive

B. Unimodal (hump-shaped)

C. Others (Waide et al.’s review)

3. Mechanisms?

A. Facilitation

i. Nitrogen-fixers

B. Complementary resource use

C. Sampling effect

4. Things to consider:

A. Supply vs. variety of resources

B. Examples mainly from grasslands

C. Temporal scale

D. Assumption of resource homogeneity

E. Spatial scale

F. Taxonomic bias

G. Proxies of productivity are not the same thing as productivity

H. Few data

I. High variance in data

Terms/people:

unimodalproductivitybiomass

potential evapotranspiration (PET)facilitationeutrophication

complementary resource usesampling effect

paradox of enrichment

productivity-

Indicators/proxies/surrogates of productivity: rainfall, potential evapotranspiration (PET), biomass, vegetation height

Diversity-productivity relationships:

I. may be positive:

- possible mechanisms:

1. facilitation-

2. complementary resource use -

3. sampling effect-

- but not always: paradox of enrichment

II. other communities exhibit a hump-shaped (unimodal) response (but see Adler et al. 2011)

- “paradox of enrichment” (Rosenzweig 1971)

- mechanisms

III.other patterns are also possible, including negative associations

Also consider:

1. If higher productivity is associated with a wider range of available resources, then species richness should increase (because different species can take advantage of different resources in different ways, thereby partitioning the available niches [topic of a future lecture]). However, a more productive environment may have a higher rate of supply of resources but not a greater variety of them. In this case, species richness might also be higher (since some species may need critical thresholds of resource levels to be met before they can persist) OR it may be lowered through dominance (e.g. by competition, topic of a future lecture).

2. Most studies have been carriedout in grasslands –> what about other biomes? (See van Ruijven and Berendse 2005.)

3. Most studies lasted only two growingseasons or reported data from a single year –> what about longer-term patterns? And some effects may not be seen until after a year of getting going. (See van Ruijven and Berendse 2005.)

4. Most studies assume resource homogeneity within a given patch. However, spatial effects may be crucial in determining species establishment, and temporal changes in resource availability or quality may also be important (Willig 2011).

5. Most studies have been conducted at small (< 0.5 ha) spatial scales. Scaling up from such local to regional properties may be perilous! (See Cardinale et al. 2004.)

6. Most studies have been carried out on plants (primary producers). What about other taxa or trophic levels?

7. Most studies have used proxies of productivity and not measured productivity directly (e.g. Mittelbach et al. 2001, Pärtel et al. 2007, Lannisto et al. 2008). Because of nonlinear relationships between proxies and actual productivity (Whittaker and Heegaard 2003; Gillman and Wright 2006, 2010; Huston and Wolverton 2009), using surrogates can lead one to misclassify the shape of the diversity-productivity relationship.

8. Many studies have few data points (i.e., are based on sampling few areas), yet determining the appropriate shape to few points can result in gross misclassification of the relationship (Whittaker 2010a).

9. Moreover, these data may have high variance (i.e., a lot of scatter), also making the true relationship (if any) difficult to determine (Whittaker 2010a).

Summary:

Diversity-productivity relationships are observed (especially positive and hump-shaped ones) for many taxa throughout the world, with animals and plants generally differing in the shape of the relationships(What is the shape of each?). The mechanisms accounting for these patterns are not clearly understood (possibly facilitation, complementary resource use, or a mere sampling effect).

Thus far we have focused primarily on richness, yet diversity = richness + evenness. Next lecture: species-abundance relationships (evenness)

References:

NOTE: Ecology vol. 91, no. 9 (2010) has a special (and argumentative!) forum on the diversity-productivity relationship. Some of the notes from this lecture were based on that forum.

Adler, P.B., E.W. Seabloom, E.T. Borer, et al. 2011. Productivity is a poor predictor of plant species richness. Science 333:1750-1753.

Cardinale, B.J., A.R. Ives, and P. Inchausti. 2004. Effects of species diversity on the primary productivity of ecosystems: extending the spatial and temporal scales of inference. Oikos 104:437-450.

Gillman, L.N., and S.D. Wright. 2006. The influence of productivity on the species richness of plants: a critical assessment. Ecology 87:1234-1243.

Gillman, L.N., and S.D. Wright. 2010. Mega mistakes in meta-analyses: devil in the details. Ecology 91:2550-2552.

Gross, K.L, M.R. Willig, L. Gough, R. Inouye, and S.B. Cox. 2000. Patterns of species density and productivity at different spatial scales in herbaceous plant communities. Oikos 89:417-427.

Hoffmann, M.D., and S.I. Dodson. 2005. Land use, primary productivity, and lake area as descriptors of zooplankton diversity. Ecology 86:255-261.

Huston, M.A., and S. Wolverton. 2009. The global distribution of net primary production: resolving the paradox. Ecological Monographs 79:343-377.

Laanisto, L., P. Urbas, and M. Pärtel. 2008. Why does the unimodal species richness-productivity relationship not apply to woody species: a lack of clonality or a legacy of tropical evolutionary history? Global Ecology and Biogeography 17:320-326.

Mittelbach, G.G., C.F. Steiner, S.M. Scheiner, K.L. Gross, H.R. Reynolds, R.B. Waide, M.R. Willig, S.I. Dodson, and L. Gough. 2001. What is the observed relationship between species richness and productivity? Ecology 82:2381-2396.

Pärtel, M., L. Laanisto, and M. Zobel. 2007. Contrasting plant productivity-diversity relationships across latitude: the role of evolutionary history. Ecology 88:1091-1097.

Rosenzweig, M.L. 1971. Paradox of enrichment: Destabilization of exploitation ecosystems in ecological time. Science 171:385-387.

Rosenzweig, M.L. 1995. Species Diversity in Space and Time. Cambridge Univ. Press, Cambridge, UK.

Trenbath, B.R. 1974. Biomass productivity of mixtures. Advances in Agronomy 26:177-210.

van Ruijven, J., and F. Berendse. 2005. Diversity-productivity relationships: Initial effects, long-term patterns, and underlying mechanisms. Proceedings of the National Academy of Sciences 102:695-700.

Venterink, H.O., M.J. Wassen, A.W.M. Verkroost, and P.C. de Ruiter. 2003. Species richness-productivity patterns differ between N-, P- and K-limited wetlands. Ecology 84:2191-2199.

Waide, R.B., M.R. Willig, C.F. Steiner, G. Mittelbach, L. Gough, S.I. Dodson, G.P. Juday, and R. Parmenter. 1999. The relationship between productivity and species richness. Annual Review of Ecology and Systematics 30:257-300.

Whittaker, R.J. 2010a. In the dragon’s den: a response to the meta-analysis forum contributions. Ecology 91:2568-2571.

Whittaker, R.J. 2010b. Meta-analyses and mega-mistakes: calling time on meta-analysis of the species richness-productivity relationship. Ecology 91:2522-2533.

Whittaker, R.J., and E. Heegaard. 2003. What is the observed relationship between species richness and productivity? Ecology 84:3384-3390.

Willig, M.R. 2011. Biodiversity and productivity. Science 333:1709-1710.