☺ WEEK 10: ABUNDANCES AND DISTRIBUTIONS , contd- ☼

Paper for Tues- Seven Forms of Rarity (1981)

Author- Deborah Rabinowitz

About the commentator: video- 

This man is the director of the Environment and Sustainability Institute, a 30,000,000-£ facility that does research, outreach to businesses to help them become more sustainable, and even reaches out to school children. I wonder how American versions of this Institute stack up. It seems really amazing and every region should emulate these people.

About the author:

Deborah Rabinowitz did her undergrad at New College, Florida, where the lush plants no doubt instilled in her a love of plants and she followed that love into a very short but fruitful career. She became interested in mangroves in Florida and worked on mangrove population ecology for her dissertation at the University of Chicago.She discovered that the existing literature, which placed the distance from the tidal shore as the most important factor influencing mangrove community makeup, was false. All the mangrove plants grew in all the tidal zones! Instead she discovered that seed size was a key dispersal factor, with larger seeds traveling farther into the sea and becoming anchored to substrate by hooking onto seaweed. Smaller seeds were more likely to germinate more inland. 

She became the first woman faculty member at the University of Michigan's Department of Ecology and Evolution Biology and then gained tenure at Cornell. Her later work on prairie grasses was the basis for her crowning achievement in science, Seven Forms of Rarity. Unfortunately cancer took this woman soon after and she didn't even make it to 40.

About the paper:

There were three different parameters for categorizing rarity in a species- range, local population density, and how many habitats it can be found in. Rabinowitz was very careful not to conflate the mechanisms the mechanics behind the cause of rarity and the ecological and genetic consequences of being rare. She also is careful to mention that rarity is not the same thing as being endangered, but there is overlap between the two ideas.

The author gives several examples of species that fit in all possible 8 permutations of these categories except one- species that have small ranges, inhabit a large number of habitats, and are rarely found. She couldn’t come up with a single example. She also says that species that are locally scarce but also have a large geographical range and live in multiple habitats are unusual and interesting but are understudied.

Rabinowitz then does a number of experiments called De wit plots, where they planted two species of prairie grasses of different proportions either 90-10% or 50-50, being categorized as locally scarce or common and allowed them to compete for space. This immediately made me think of the “colonizer vs equilibrium species” concept from Fenchel 1974 if you think of each plot as an island. The relatively rarer species actually outcompeted the more common species. The rare ones could be thought of as the colonizer species, with the more common ones being considered the equilibrium species. It would have been interesting to see how long Rabinowitz allowed her De wit plots to run and where they would be during longer experimental periods. She also found that the size of rarer species were larger when rare and common species were larger when they were common.

At first glance this is ludicrous. As she states, rarity can not be a viable evolutionary strategy. Natural selection for rarity?! Darwin’s theory of evolution of natural selection of the loneliest???

Random thought I had- plants are not at all my thing. The selective pressures are more abstract and alien to me. We all know that when we follow energy in animal trophic levels, we lose approximately 2 orders of magnitude of available energy. It’s why its super obvious that’s why an environment can sustain way way less apex predators than primary consumers. Plants though… plants in a particular population, at least until they start covering each other up, have equal energy within their disposal. The sun will provide both you, your neighbor, and your sister with the same approximate 100 W/m^2. In a way, being a plant is the ultimate form of socialism. Everyone is on the same playing field. Everyone has the same ultimate source of energy and everyone gets his own slice of the pie. Of course there are things like microhabitats and soil quality that may differ but plant and animal ecology are two completely different worlds.