Term
Productivity (define)
What measures of productivity are used? |
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Definition
Productivity is the rate at which (potential) energy flows through an ecosystem (kj/m2/yr).
Primary Productivity
1) The rate of change of plant biomass (g/m2/yr)
2) The standing crop of plant biomass (g/m2)
What measures of productivity are used?
PET: Max amount water lost from leaf surfaces due to evapotranspiration when water is not limiting; reflection of the energy available to evaporate water to the atmosphere and thus depends also on wind velocities.
AET: Measured amount ofwater lost from leaf surfaces due to EvapoTrans
other... rainfall, temperature, resources.... |
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Term
| Hawkins et al (2003) Ecology |
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Definition
Looked at productivity-diversity relationsips at continental scale: # of spp over increasing PET.
Found a more or less unimodal distribution for diversity - with maximum diversity at intermediate levels of productivity.
As you change the scale, different factors become limiting.
-Above a certain latitude, energy is limiting. Below it, water is limiting. |
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Term
| What are the ultimate determinants of animal diversity? |
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Definition
1) animal productivity
2) plant diversity |
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Term
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Definition
Huge review - how many times do papers support four relationships within and across communities: 1) unimodal, 2) positive, 3) negative, 4) none.
Didn't control for scale
Found that there were all sorts of explanations, varying within and across communities, as well as for plants and animals. |
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Term
| What are the 4 components of scale? |
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Definition
| extent, grain, focus, sampling unit |
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Term
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Definition
Scale is important!
Scheiner et al (2000) EER:
-took the same hypothetical set of regions,, communities, and landscapes to show that diversity vs productivity curves may look entirely different depending on the scale at which the analysis is performed.
Chase and Leibold (2002)
-spatial scale affects the form of the relationship (same as above)
-local scale (diversity within a community) vs regional scale (diversity across many communities)
-found unimodal distributions at the local scale and monotonic at regional (ponds).
Simpson's paradox: scale at which you aggregate data can determine outcome. (Maybe we've been arguing for nothing over richness/productivity??) |
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Term
| Assuming that there is a productivity/biodiversity relationship, how do we explain it?? |
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Definition
| According to Rosenzweig and Abramsky (1993) there are 9 hypotheses. Here are 4: 1) More individuals/Energy 2) Environmental heterogeneity or "more specialization" 3) Disturbance-productivity dynamics 4) one more trophic level |
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Definition
| 1) Productivity is limiting 2) More productive sites support more individuals 3) Species richness increases with the number of individuals (apportionment (the cake)) 4)therefore, more species at more productive sites Prediction: increasing (Hutchinson 1959, Brown 1981, Wright 1983) |
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Term
| One more trophic level: keystone predation |
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Definition
| 1) number of trophic levels is limited by energy input 2)adding a trophic level by increasing productivity (resource input) will suppress dominant prey populations. 3) Competitive exclusion amongst prey is less likely 4) Therefore, the addition of trophic levels at more productive sites can lead to predator-mediated increases in diversity (Paine 1966) Prediction: unimodal * You can get unimodal relationship if more energy flows and you get a destabilized system (ie. fluctuations of predator prey populations) |
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Term
| Environmental Heterogeneity: "More Specialization" |
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Definition
| * adding resources allows you to add more species. Prediction: linear 1) productivity = availability of difference resource states or types 2)a minimum amount of resource is required to support a specialist 3) increasing productivity increases resource availability and more specialists 4) specialization prevents competitive exclusion, so greater productivity = more species prediction = linear (Abrams 19995) Ecology *eg. bacterial speciation occurs more rapidly with an O2 gradient (Kassen el al 2000, Nature) |
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Term
| Disturbance-Productivity Interaction |
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Definition
| 1) More productivity = faster growth rates 2)faster growth rates = faster population recovery after disturbance 3) populations at low abundance, due to disturbance, are more likely to suffer extinction if they recover slowly 4) therefore, more species at more productive sites, as long as disturbance frequency is not too high or low. Prediction: variable outcome (some times up, down, or unimodal) |
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Term
| Productivity-diversity Conclusions |
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Definition
| Species Diversity is constrained by the productivity of the environment both at large and small scales, but not universally so. Whether the relationship b/w prod and diversity within communities is unimodal or linear depends upon the taxon and scale: this remains a controversial topic. Theory provides several explanations for both types of relationship: eg. more individuals, specialization, disturbance and trophic constraints. Evolutionary theories are also relevant (e.g. speciation rates). Convincing experiments are few but increasing in number. Theories that consider several explanatory variables and scales together will be the way forward. |
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Term
| Chase and Leibold (2002) Nature |
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Definition
"Spatial scale dictates the productivity-biodiversity relationship"
the shape of the relationship should vary if different mechanisms are responsible for diversity at different scales
-found hump-shape relationship locally, and monotonic regionally
-reason is that higher productivity = local dissimilarity within region
-found that species dissimilarity increased with productivity
-individual ponds in regions with higher productivity had few spp, but composition b/w ponds was different
Take home message
-scale matters because dissimilarity is predicted by productivity
Key Concepts (to explain dissimilarity)
-spatial heterogeneity (rejected)
-temporal variation (couldn't test)
-multiple stable states (couldn't test)
Implications
-reserve design
-managing for hotspots, not regions
-maybe we have to sacrifice local for regional diversity |
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Term
| Three mechanisms could cause spp dissimilarity to increase with productivity |
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Definition
| 1) regions with higher productivity may have higher degree of environmental heterogeneity (did not find this in Chase and Leibold study) 2) regions with higher averave productivity may also have a higher propensity for temporal variation in local spp composition 3) community composition can strongly depend on the order in which spp initially entered a community (multiple stable states) |
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| Questions regarding Chase & Leibold 2002 |
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Definition
Is it possible that a unimodal relationship exists at the regional scale as well but that it is not evident in this design??
-i.e. monotonic increase in first part of local scale relationship could be analogous to what we see at regional scale
-ponds in a watershed = samples in a pond??
-scale difference
2)Is there a third variable that controls both productivity and biodiversity? (ie. they never mention why certain regions are more productive). |
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