Week 4: Macroecology before Macroecology (cont.)
Paper
for Thursday, Feb. 9: Net Primary Productivity of Terrestrial Communities:
Prediction from Climatological Data (1968)
About the commentary author: S. K.
Morgan Ernest
We’ve already heard from Ernest in past
discussions. Ernest is a biologist at the University of Florida studying
macroecology and community ecology. She conducts much of her research with the
Portal Project, a research site for long-term ecological studies in the desert.
About the author: Michael L. Rosenzweig
About the author: Michael L. Rosenzweig
Dr. Rosenzweig received his PhD in in
Zoology in 1966 from University of Pennsylvania. He hopped around from school
to school as a professor for a few years (even landing at UNM from 1971-1975)
before founding the Department of Ecology and
Evolutionary Biology at the University of Arizona, where he’s been since
1975. Among his interests are species diversity, desert mammal ecology, and
environmental issues, and he focuses much of his efforts on species-area
relationships (this study led him to develop “reconciliation ecology”). He has
been an editor for Ecological Society of America since 1977, among others, and
founded [the journal] Evolutionary Ecology Research.
Cliffnotes:
In this study, Rosenzweig hopes to find a way to quantify energy flow through a community. He gets this idea from earlier studies that attempt to find relationships between diversity and productivity, and the abiotic factors affecting this, but the influences were not quantified in these studies. Specifically, Rosenzweig tries to find one abiotic variable in the system that can predict primary terrestrial production. His hypothesis revolves around “actual evapotranspiration” (AE) of plants in a community – AE is the amount of water actually being transferred into the atmosphere through evaporation and transpiration, and is an effect of both water in the system and solar energy required for these processes to take place.
Data for this study are collected from various climatological datasets and studies on production and AE of various environments across latitudes. Rosenzweig came across a few issues to correct for when collecting his data; namely, a lack of AE and production values collected from the same location, arid environments with lots of runoff, different AE processes in higher altitudes, and young vs. mature communities. He plots all his data in log units as a regression line and acquires an equation of net annual above-ground productivity (NAAP) based on actual evapotranspiration.
In this study, Rosenzweig hopes to find a way to quantify energy flow through a community. He gets this idea from earlier studies that attempt to find relationships between diversity and productivity, and the abiotic factors affecting this, but the influences were not quantified in these studies. Specifically, Rosenzweig tries to find one abiotic variable in the system that can predict primary terrestrial production. His hypothesis revolves around “actual evapotranspiration” (AE) of plants in a community – AE is the amount of water actually being transferred into the atmosphere through evaporation and transpiration, and is an effect of both water in the system and solar energy required for these processes to take place.
Data for this study are collected from various climatological datasets and studies on production and AE of various environments across latitudes. Rosenzweig came across a few issues to correct for when collecting his data; namely, a lack of AE and production values collected from the same location, arid environments with lots of runoff, different AE processes in higher altitudes, and young vs. mature communities. He plots all his data in log units as a regression line and acquires an equation of net annual above-ground productivity (NAAP) based on actual evapotranspiration.
Rosenzweig finds a correlation between AE and NAAP. He explains that photosynthesis, an integral part of productivity, is affected by solar energy and water, and AE is a measure of these two variables. Although this study supports the idea that AE predicts productivity in mature terrestrial communities, more studies need to be conducted on different aspects of the study. He lists mature vs. young and variation in transpiration as possible further steps. Although it only presented a correlation, this paper provides groundwork for more specific productivity studies, including latitudinal diversity gradients and the species richness-energy Hs.
A few things to mention. Evapotranspiration as a proxy for primary productivity? Brilliant.
ReplyDeleteBut what about environments that always have very high relative humidity? I.e. Rainforests, wetlands, etc. where the air is usually saturated with water vapor and plants can't respirate effectively? What about just measuring air moisture concentration as a whole instead specifically targeting evapotranspiration?
Sorry... It might not make sense... I wrote that yesterday but I couldn't posted... Here is what I wrote yesterday:
ReplyDeleteTo start my comment, I would like to point out that the author didn’t specify very well how NAAP or AE were actually measured. This made it hard for me to understand where the numbers in the table came from and what they actually mean. What I got out from this paper as pretty basic summary (and from the only figure present) is that the water available in a system is directly correlated with the biomass production (and/or lost because at the end NAAP is grams of dry matter/m2). That makes a lot of sense but, most important than the dry matter in a system is the biomass energy that is available to this system, where microbes have a really important role. Also, the author only considers mature communities that are in a “climax” state but he never defines what is “climax” to him. Is there such a thing as “climax” vegetation? What about the fact that the author only considers mature communities? Are mature communities climax vegetation communities?