Paper 13 - R. Kiat

Paper 13 – R. Kiat

Fenchel, T. 1974. Intrinsic rate of natural increase: the relationship with body size. Oecologia 14:317-326.

Commentary -- Richard M. Sibly

Tom Fenchel

-        Professor Emeritus at the University of Copenhagen , Marine Biology

-        PhD from the University of Copenhagen

-        Research Interests: Microbial Ecology and physiology, Marine Biology, Evolutionary Biology

Richard M. Sibly

-        Professor at the University of Reading, School of Biological Sciences

-        Research Interests: Integrating Life History Theory with the new theory of Metabolic Ecology. Using Agent Based Models (ABMs) to develop new methods in Population Ecology applicable to real landscapes.

Summary:

How fast can a species increase its population size and how might this be related to its body size? In this paper, Fenchel demonstrates a relationship between “the intrinsic rate of natural increase” of a species (r_m – also commonly known as population growth rate and in this instance measured in days) and a species body weight by looking at 42 different species from literature. His results show that smaller species (with lighter weight measured grams) have a higher population growth rate than bigger species.

By viewing r_m as a form of productivity, Fenchel then makes a connection of body size and metabolic rate. In Figure 2, Fenchel highlights the previously found relationship between the two which shows that smaller animals have a higher metabolic rate, which he says can be viewed as a measure of how much energy an organism uses for productivity e.g. reproduction vs. maintenance. By comparing organisms based upon ‘complexity’, Fenchel argues that move evolved organisms had a higher metabolic rate per unit weight, which might be explained energetically by higher maintenance in the organism – proportionally more energy is allocated to maintenance.

On a broader context, Fenchel’s paper and his framing is important in light of viewing population growth rate and body size in terms of energetics – which is still a topic of wide interest (as Sibly mentioned in the commentary).

Note: Fenchel notes that the 42 species he selected which included rats and microorganisms, were mainly limited to laboratory studies (which he suggests might be a bias selection for certain type of species).

Questions:

What other constrains might there be that relate to a species body size? Thoughts on Fenchel’s law? Figure 3? Are there other ecological concepts previously discussed that we might be able to talk about in terms of energetics?

Paper 14 - T. Hawkins

Population density and body size in mammals

By John Damuth

Foreword by Aistair Evans

John Damuth is a research scientist at the University of California Santa Barbara Marine Science Institute. His research includes ecological correlates with body size.

Alistair Evans is a Research Fellow and Senior Lecturer at Monash University. His research includes the evolution, development, and function of animal morphology.

Body size is very important to an organism. From an ecophysiological perspective, body size is very closely linked to the energy input in the environment (Bergmann’s Rule, Temperature-size Rule). What does that look like at the population level? To answer that question, Damuth compiled data from herbivorous mammals. More specifically their body size and population abundance, which he compared with metabolic rate. What he found was that while body size grows exponentially with energy use, population abundance decays at an equal rate. Which makes sense. The energy has to be conserved somehow.

Questions:

How do these manifest at the community level? My first thought is how it would work as a mechanistic explanation for the “ten percent rule” but are there other ways they interact?

Paper 31 - By K. Sullivan

Paper 31

Brown, J.H. 1984 On the relationship between abundance and distribution of species.  American Naturalist 124:255-279

Blog by Kaitlyn Sullivan                                  

Paper Author: James H. Brown

(Commentary by Christy M. McCain)

Christy M. McCain

·      Ph.D. from University of Kansas

·      Associate Professor and Curator of Vertebrates Dept. of Ecology & Evolutionary Biology and University of Colorado Boulder Natural History Museum

Research interests:

“I am interested in the mechanisms producing and maintaining patterns of species distribution, abundance, and diversity. To address these processes, I consider three levels of ecological organization to be equally important: species-level autecology, population-level dynamics, and community-level processes and interactions. My research so far has highlighted small mammal range dynamics, abundance patterns across altitudinal ranges, and species richness patterns along latitudinal and elevational gradients. I particularly exploit mountain systems as natural experiments to look at how evolutionary history, ecological processes, and future climate change influence species populations. My overarching goal is to strive for quantitative, general theories applicable to both the advancement of ecology and the improvement of our conservation strategies. I use multiple tools at various spatial scales to address research questions, including field studies, synthesis of collection and historical data, comparative analyses, null models, GIS, and simulation modeling.”

Christy M McCain. (n.d.) retrieved from http://www.colorado.edu/ebio/christy-m-mccain

James H. Brown        

·      Professor of Biology at the University of New Mexico

·      Bachelor of Arts, Zoology, 1963, Cornell University

·      Ph.D., Zoology, 1967, University of Michigan

Research Interests:

“Community ecology and biogeography, with special projects on granivory in desert ecosystems; biogeography of insular habitats; and structure of dynamics of geographic-scale assemblages of many species.”

Department of Biology at UNM, http://biology.unm.edu/core-faculty/brown.shtml

Summary  

His paper examined the various patterns and theories surrounding “spatial variation in abundance within species”.  Using various data, he demonstrates the greatest population density across a species range occurs in the center and declines towards the range boundaries.  He noted two assumptions in his explanation for this.

1.     “a species’ range corresponds to its environmental niche”

2.     “those environmental niche variables are spatially autocorrelated.”

He argued that for this to be true, then highest abundance should occur at the center of the range as it provides optimal environmental conditions.  He coined this the ‘abundant center’ pattern, and claims it can be “defined by a normal probability density function”. 

            Secondly, his paper examined the primary patterns and theories regarding positive correlation between abundance and distribution of related species.  He argued that if species could gather enough resources to support a larger number of individuals in an area, that species should also be able to sustain many smaller populations in a large number of sites.  Species with similar niches, who are not able to gather as many resources however, cannot support large populations and will be restricted to fewer sites.  His last assumption on which his ideas were based, was that “similar and related species share substantial portions of their niches”.

            Brown poses his question: “Is there any general pattern of spatial variation in abundance within the area in which a species normally occurs?” Following this up with: “yes, density is greatest near the center of the range and declines, usually gradually, toward the boundaries”.

Questions:

-       In his summary, Brown argue that “most exceptions to this predicted pattern can be explained as cases in which assumptions of the model are clearly violated.”  What does he mean by this?

-       What implications has this had towards other statistical models?

Paper 29 by Rebecca Kiat

Paper 29 by Rebecca Kiat

Rabinowitz, D. 1981. Seven forms of rarity. Pages 205-215 in H. Synge, ed. The biological aspects of rare plant conservation. Wiley, New York.

Paper Author: Deborah Rabinowitz

(Commentary by Kevin J. Gaston)

Deborah Rabinowitz

-       Ph.D. from the University of Chicago

-       First female faculty member in the Department of Ecology and Evolutionary Biology at the University of Michigan

-       Tenured at Cornell in e Section of Ecology and Systematics within the Division of Biological Sciences until August, 1987

-       Passed away at the age if 39 in August 1987 from cancer complications

“Although Deborah had only twelve years between her Ph.D. degree and her death at the age of thirty-nine, she made substantial contributions to the general field of plant population biology. By far her most significant contribution is to our understanding of why some kinds of plants are so much less common than others. The question of differences in species abundances has had a long history of interest in ecology, but Deborah brought to it a fresh and highly original approach. In 1981 she published a landmark paper in which she described seven different meanings of the concept of “rarity”.” – From University of Cornell commons website

Kevin J. Gaston

-       Ph.D. from the University of York

-       Founding Director of Environment & Sustainability Institute, University of Exeter

Professor of Biodiversity & Conservation, University of Exeter

-       Website: http://kevingaston.com/

“I lead basic, strategic and applied research in ecology and conservation biology, with particular emphases at present including common ecology, ecosystem goods and services, land use strategies, and urban ecology.” – From University of Exeter website

What makes a species rare? What makes some species more scare compared to other species e.g. is it due to inferior competitive abilities?

There are different ways a species can be rare. As Rabinowitz mentions, a species may have large local abundances but they may only be found in specific, limited habitat types, while other species may be very common across different habitats, even though that species is never dominant in any one of those habitats (low population size).

In her chapter, “Seven forms of rarity”, Rabinowitz discusses a theoretical framework of a way to classify rare species with different forms of rarity using examples from North American flora. Rabinowitz also discusses experimental studies she conducted (Harper 1977: de Wit plots) with prairie grasses from Missouri to assess competitive effect on abundance in terms of population size as well as the size of the individuals.

-       Focus on exploring the biological (evolutionary and ecological) consequences of rarity.

-       Note: Difference between causes of rarity and consequences of rarity.

-       Rabinowitz proposed a simple scheme to focus thoughts instead of focusing on specifics with monolithic rarity – allow for further discussion when looking at species comparatively instead, perhaps allowing for a shift in perspective.

A classification of rare species

Three categories for rarity:

i)              Geographic range – large vs. small

ii)            Habitat specificity – wide vs. narrow

iii)          Local populations size – large, dominant vs. small, non-dominant

-       Used these categories to form a 2 x 2 x 2 block to compare between and look at different species.

-       Talk about results vs. processes that result in observed rarity

-       Extinction – In light of these categories, how might this affect the risk of a species to extinction?

Examples:

o   Demographic stochasticity with small samples in causing local extinctions

o   Habitat destruction – species endemic to mangrove swamps even if locally common may be subject to high risk with anthropogenic intervention

-       Importance of comparisons: “Monitoring rare species (for instance, Bradshaw's long term assessments of the Teesdale rarities) tells us a lot about the characteristics of these taxa. However, in the absence of comparative data for related common taxa, essentially control species, we cannot judge whether the traits of rare plants are unique to them or are some random sample of plant traits in general and unrelated to the rare state.”

Competitive abilities of sparse species

-       Prior claims – a species is rare because it is an inferior competitor?

-       Setup of de Wit plots to compare competitive effect of different species on abundance and size of plants – different proportions of each species in pairwise experiments with combinations of rare and/or common species

-       Compare monocultures with yield when grown in pairwise setup

-       General results:

o   Sparse grasses yields fall ABOVE expectation with monocultures.

o   Common grasses yields fall BELOW expectation with monocultures.

o   Conclusion – Rarer species are superior competitors? Other factors that may result in rarity?

-       Note: Is abundance the only way to gauge the success of a species?

Natural selection and sparse species

 – What are the other factors that may explain why a species is rare?

-       Advantage to a rare species only when it is rare?

o   E.g. density-dependent fungal pathogen being a limiting factor with chestnut species