Paper 39: Simberloff and Wilson, Experimental Zoogeography of Islands: The Colonization of Empty Islands

I already liked E. O. Wilson before reading this paper, but after reading I have a new found appreciation for Wilson, Simberloff, and others that put abstracts in the beginning of their papers. As mentioned in the section introduction, this paper built on the theory of island biogeography and species equilibrium proposed by Wilson and MacArthur by actually testing the theory experimentally.

Experimental Design

The design of this experiment is nice in its simplicity, although I question whether it is a design that researchers would be able to repeat nowadays. Simberloff and Wilson Performed their experiment on a set of mangrove islands in the Florida Keys. A survey of the arthropod fauna of each island was done prior to defaunation, which is a great word I think, by tenting the tree island and gassing it to kill everything. Periodic surveying was then done for the next year to document what species colonized the island and when. An entire section of the paper was devoted to an explanation of why certain species were not included in their study. This was also their methods section where terms used in the rest of the paper, and how they recorded their data, are defined.

Seasonality

I liked this section. Basically Simberloff and Wilson explain in detail how the Florida Keys completely lack anything that could be considered seasonality, and because of this they don’t think seasonality is a factor for colonization of an empty island in their system. They did try to see how differences in wind patterns might be correlated to colonization, but were not able to acquire detailed enough measurements for any conclusive results.

Patterns of Colonization

It is beneficial to have a background in entomology for this section I think. I don’t have that background so a lot of these names sound really cool, but I didn’t know what they were talking about. The overall concept here though is that there is a pattern to colonization of an empty island. The early colonists are usually strong fliers that can make it to the island the easiest. The final colonists are ants, which Simberloff and Wilson paid special attention to. That makes sense since Wilson is an ant guy. The other notable pattern is that predictability of colonization increased with later colonists. Early colonists appeared and died, but the later colonizers were more stable.

Colonization Curves

Ecologists really like math. So, the colonization curves seen in figures 1-3 are pretty cool. This is what Simberloff and Wilson were counting in this experiment, how many species colonize an empty island and what is the time frame for that colonization. The cool thing here is that each curve approaches the number of species present prior to defaunation and sort of hangs out around that number. The significance of this finding is that it supports the proposed concept of an equilibrium in the number of species present on an island. Here is the first equation in the paper, but all the equations are nice and simple. I think this is the coolest part and will hopefully garner some interesting conversations in class.

Dispersal

This is a rather long section for a somewhat simple concept. Here Simberloff and Wilson discuss the mechanism of dispersal for colonization to the islands. The take home here is that if you are an arthropod and want to go to a cool new island do not try to swim there no matter what. Fly there if you can using the wind to your advantage, and if you can’t fly get on a nice leaf and still let the wind take you there. If you end up in the water you will be so dead so fast, and all of your little arthropod dreams of setting up a cool dive shop on a soon to be discovered awesome island for retirement will wither away to nothing in the gut of a fish that cares nothing of you or your little arthropod spawn.

Immigration and Extinction Rates

This is the crux of the theory under test in this experiment.  The model by MacArthur and Wilson for island biogeography really comes down the immigration and extinction. Early on the immigration rate exceeds the extinction rate and the number of species occupying an island increases with extinction rate not being affected by interaction between species. As the number of species increases and the populations of different species also increases then interaction between species increases and the extinction rate increases. For each island there is a certain equilibrium dictated by the size of the island and the distance from the mainland, or source. When below this equilibrium immigration rate exceeds extinction rate until you approach or go beyond the equilibrium. At equilibrium the immigration rate and extinction rate are pretty much the same, hence it being at equilibrium. So there you go. All of your questions about island biogeography have been answered and we can spend Tuesday eating cake.

Paper 38: Food Web Complexity and Species Diversity

Paper 38: Food Web Complexity and Species Diversity

Robert T. Paine

image source: http://www.washington.edu/news/2013/07/30/fifty-years-of-ecological-insights-earn-uw-biologist-international-award/

Background: Paine (pictured above in Makkaw Bay) is a retired professor emeritus at the University of Washington. Paine coined the term keystone species. Paine thought apex species increase species diversity.

Hypothesis: Local species diversity is directly related to the efficiency with which predators prevent the monopolization of major environmental requisites by one species.

Application: Local diversity patterns of rocky intertidal marine organisms.

Conclusion: Predatory species are in relatively greater proportion in diverse situations.

The Structure of Selected Food Webs

Subwebs are groups of organisms capped by a terminal carnivore. Subwebs have top predators that appear to be distinct, known later as an apex predator.

North temperate subweb

The Pacific Coast in Washington community intertidal organisms found on rock substrate included: mussels, barnacles, and one starfish. The carnivores in the system were Pisaster ochraceus (starfish) and Thais emarginata (muricid gastropod). The food web is tied to the barnacle community and both predators feed on them. The ratio of carnivore species to total species is 0.18.

Subtropical subweb

The Northern Gulf of California’s community is more complex than the previous subweb. The structure includes a starfish (apex carnivore), carnivorous gastropods, herbivorous gastropods, bivalves and barnacles. Paine says this ubweb has increased trophic complexity. The ratio of carnivore species to total species is 0.24.

Tropical subweb

The Mate de Limon off the Pacific shore of Costa Rica did not have a secondary carnivore. The community consisted of two muricid gastropods (Acanthina brevidentada and Thais biserialis) and mytilid and barnacles. This is a simplistic system compared to the north temperate and subtropical subwebs.

Predation and Diversity Gradients

The removal of the apex predator (Pisaster - starfish) decreased diversity in the community, and the system became simplistic. Paine concludes that predation is a positive feedback loop because predation prevents resource monopolies and thus allows for diversification in a community. There was not a relationship between latitude and diversity in this study, but increased stability could increase the capacity for higher-level carnivores.  

 

Questions:

1. This study assumes the probability of bivalves being eaten is proportional to abundance. Do you agree with this assumption? If not, why?

2. Paine uses the measurement calories. What measurement might we use in a modern study and why?

3. Paine states high calorie foods have greater nutritional value. Do you agree that more calories means greater nutrition?

4. Paine seems to ignore stochastic events and anthropogenic influence on the intertidal marine ecosystems. Do you think stochastic events or anthropogenic factors could have influenced his data, especially his results in the tropical subweb?

Experimental Studies on Predation: Dispersion Factors and Predator-Prey Oscillations, C.B. Huffaker

Introduction

Two types of fluctuations reduced densities and amplitude of fluctuations, compared to when predators were absent.

A.)  Exclusion of predators caused a pattern of fluctuations of decreasing amplitude

Example: Reciprocal density-dependent interaction of the phytophagous mite and host plant.

B.)  Contrasting type of pattern of fluctuation

Example: Predation on the phytophagous mite.

Huffaker questioned if Gause theory sufficiently described predator prey relationships. He supported his idea with Nicholson’s criticism of Gause’s experimental design as being too small to approximate qualitative or quantitative results. Huffaker was also influenced by DeBach and Smith’s experiment on the searching capacity of predatory parasites using Nicholson’s formulas. Huffaker took a quantitative approach to a laboratory experiment of continual (not self-exterminating) predator-prey relationships.

Experimental Design and Procedure

In this experiment, the six-spotted mite, Eotetranychus sexmaculatus, was the prey species and Typhlodromus occidentalis was the predator species. Oranges were kept in the dark, at 83 degrees F, and in greater than 55 percent humidity. Food quality and feeding area were altered to various degrees by wrapping the orange in paper and/or paraffin. Six-spotted mites were cultivated on lint covered oranges. A continuous system was developed by removing and replacing oranges. At 11 day intervals, ¼ of the oldest or unsuitable oranges were removed and replaced. The experiments were initially in duplicates, but as experiments failed, new improved experiments were created and substituted in.

A “universe” was created using oranges and similarly sized rubber balls in a 40 inches long by 16 inches wide trays. The tray had a 1 inch side wall covered in petroleum jelly to prevent mite movement in or out of tray, and 40 Syracuse watch glasses on each orange or rubber ball.  Increasing the area with rubber balls complicated the search for food by prey and predator. Predators and prey unable to leave or enter the universe, but both predator and prey were allowed to move freely in the universe.

To make counting easier, diameter lines were drawn on the surface of the exposed surface and divided into 16+ numbered sampling sections. A portion of the mites were counted then multiplied to estimate the total populations, and the total populations were counted in small samples. Statistical analysis showed estimated samples have a loss in confidence. Subsamples of an orange were better estimated by two or more non-contiguous areas evenly distributed with a proportion of ½ or ¼ the total exposed area on each orange. Small changes in population might be undetectable due to sampling procedure, but the sampling is adequate and accurate for major trends or patterns of population change.

Results

The present experiment showed oscillation between prey and predator under laboratory conditions. If we take into account the absence of predator, the prey population will persist through time, but once the author added another predatory mite both of them, predator and prey will become extinct. Complex habitats were created, which reduce predator’s dispersal and therefore predation upon preys. These microhabitats which were created experimentally increased heterogeneity and produced stabilizing effects in the oscillations previously reported.

Discussion

The section introduction really saves us from Huffaker’s writing in this paper. The take home message that I think, with the help Real’s intro, Huffaker is trying to portray is that the patchiness of an environment directly affects the survivability of prey due to increased search time by the predator, and more possible refugia both in space and time for prey. This paper seems to scream that it is the experimental aspect of McArthur and Pianka’s paper about optimal use of patchy environments, however that paper was published 8 years later so that is likely not an accurate statement. The concept of predator-prey oscillations I think is something familiar to us all, with a classic example, again from our high school and undergrad textbooks, being the oscillations of snowshoe hare and lynx. It would be interesting to look at how the patchiness of the environment might provide local refuge from predation for the hare across their range, and other systems outside of a laboratory setting.

Paper 37: The influence of interspecific competition and other factors on the distribution of the barnacle Chthamalus stellatus

Here is another great study that I am sure many of us remember from our youth. Hold on dearly to these memories for I can attest to the negative effects of being a graduate student. Already the proportion of gray hair atop my head has increased dramatically, and the absolute number of said hairs would also have increased tenfold I am sure if not for the additional increase in my rate of hair loss. So, I repeat, hold onto these memories of your youth for they are all you have now that life is heading down hill so quickly, and the stresses of life are increasing “exponentially” (I totally pay attention to your math lessons Helen.)

Okay, let us begin with my summary, or one can head to the end of the paper for a very nice summary by the author Joseph H. Connell, who is still alive and very old. 92 years old to be exact. Connell is an American ecologist, but, since his study on how interspecific competition regulates the distribution of the barnacle Chthamalus stellatus was conducted on the shores of Scotland, I personally think he should be referred to as Sir Joseph Connell because the United Kingdom is the land of knights and chivalry, and everyone knows that academics are the epitome of chivalry and honor. However, I am not the queen and therefore cannot bestow such an honor so I will call him Connell.

Connell starts off his paper with an observation on the shores of Scotland. He noticed that the adults of Chthamalus and the adults of Balanus balanoides are separated into two distinct zones with the smaller Mediterranean Chthamalus distributed mainly above the tide level, and the arctic Balanus distributed at and below the tide level. Connell also noted that while he observed young Chthamalus below the tide level intermixed with the Balanus, he saw very few adult Chthamalus below the tide level. Something must be at play that is separating these two species of barnacle on the majestic coast of Scotland, and Connell was set out to discover what this was or die trying.

And bravely we soldier on into the rather detailed, and dry, methods section. So, who had to look up what a spring tide and neap tide are? Don’t lie, Christmas is just around the corner, and if we all get coal then London will be polluted again and all the typical moths will be eaten. I know I had to look up what these two kinds of tide are, but we can discuss the specifics in class; in short these two kinds of tide are tied (pun intended) to the relative positions of the sun and moon, and were used in conjunction with the mean tide level as demarcations for the distributions of the two barnacle species in question. I don’t think it is very effective to go through piece by piece what exactly Connell did, so I will try my best to be concise. Basically, Connell had several areas of different depths where he mapped the locations of barnacles for several years. At each area there was a control portion that he did not remove the presumed dominant species, Balanus, and an experimental portion where he did remove Balanus. In order to test for competition at depths where Chthamalus did not occur he performed translocations of stone with barnacles already attached. Connell also tested for the effect of a predatory snail on barnacle distribution at several testing areas by using a mesh cage to prevent predation.

(It’s a Scottish fold, the primary predator and snuggler in Scotland)

Enough with that methods jazz, onto the results, which is the real meat of any paper. Connell Briefly discusses physical factors that play into the distributions of Chthamalus and Balanus. The main point to take away from this section is that Chthamalus appears to be capable of surviving at a higher level than Balanus due to a greater tolerance to heat and desiccation. This explains the upper limit of the distribution of Balanus; they simply can’t survive being dried out and baked as well as Chthamalus. In addition to this Connell also pointed out that the data suggests that Chthamalus is capable of surviving at deeper depths than it is currently found at, meaning that there are other factors contributing to the lower limit of Chthamalus.

Now we move on to the crux of the paper, competition for space between the two species. Figures 2 and 3 sums up this paper quite well actually. Each graph represents a study area with the horizontal axis being time in months, and the vertical axis being total number of Chthamalus in the study area. The dotted line on the graph is the number of Chthamalus in the study area where Balanus was removed, and the solid line is the number of Chthamalus in the study area with Balanus present. A majority of the graphs show the same trend; Chthamalus survives longer when it is not living, however short that life might be, sympatrically with Balanus. Connell provides several tables of ancillary data in regards to how Balanus either directly kills or removes Chthamalus when they are competing for space, and other details about mortality rates. Figure 4 is not from Connell’s study, but shows that survival of Chthamalus is negatively correlated to the growth rate of Balanus.

Connell, again briefly, discusses the effects of predation by the snail Thais. What is significant in this section is that predation by this snail does not explain the distributions of these two barnacle species, but, interestingly, it does lessen competition. Connell proposes that the mechanism by which Thais reduces competition is by preferentially preying upon larger barnacles, which happen to usually be Balanus. This would obviously reduce competition between Balanus and Chthamalus because it lowers the population of Balanus.

I remember reading about this study as an undergrad, and it was just a given that Balanus is a better competitor than Chthamalus. It was never explained exactly why or how Balanus out competed Chthamalus. Lucky for us Connell does just that in his discussion section with his part on “The Causes of zonation.” Connell ends his section on competition for space with a quote from Elton and Miller (1954) defining interspecific competition as “in which one species affects the population of another by a process of interference, i.e., by reducing the reproductive efficiency or increasing the mortality of its competitor.” In this final section Connell explains how Balanus does just this to Chthamalus. And for anyone teaching a 203 or 204 lab, you can use this as an example of a redundant sentence since I said basically the exact same thing before the quotation. According to Connell, Balanus directly affects the fitness of Chthamalus by increasing mortality of adults through physically smothering or removing adults from an area, but also indirectly affects fitness by deforming and reducing the size of adult Chthamalus, which in turn decreases the amount of larvae produced thus reducing reproductive efficiency. Balanus is able to do this because of two traits; One, Balanus produces more larvae resulting in a larger population density relative to Chthamalus; and two, Balanus has a faster growth rate than Chthamalus. These two traits allow to Balanus to out compete Chthamalus when the two species exist sympatrically.

The last section is Connell’s wonderful summary that you could read and skip mine, but hopefully this has been somewhat entertaining and informative, now for some questions.

What exactly makes this a foundation paper and why is it included? (Everyone has to ask this question so cut me some slack)

How does this paper deal with interspecies interactions in comparison with Kettlewell and Park? What is the ultimate conclusion to the interactions in each of these systems?

Is Billy Connolly Scottish, or over the top Scottish?

I thought that the experimental design was robust, but I am sure people can find holes and flaws, what might these be?

It was mentioned both in the introduction to this section and Connell’s introduction to this paper that part of the beauty of this system is that the two competing species are sessile, how might one accurately test for completion in a more complicated and mobile system?

           

            Do I actually know how to use a semi-colon, or was I randomly throwing them in there for brownie points?

             

            This entire section for experiments in the lab and field is animal centric when a majority of what we have read up till now has been looking at plants, why do you think that is?

            How could Mel Gibson go from making Braveheart to The Beaver?

           

Biston betularia color morphs (For paper 34)

Biston betularia color morphs (Images are not mine)
A. typical
B. insularia
C. carbonaria

 

 Ecology reading Part 6

Hi all,

On Tuesday (October 27th ), we will be discussing the following papers: Selection Experiments on Industrial Melanism and Competition between  populations of the flour beetles, Trilobium confusum and Trilobium castaneum

Paper 34. Selection experiments on Industrial Melanism

1. Author: 

Dr. H.B.D Kettlewell (1907- 1979). British Medical Doctor, Lepidopterist and Geneticist.  He is well known for a classical study on natural selection using as a model organism peppered moths (Biston betularia).  Kettlewell conducted a series of experiments in 1950 on the phenomenon of industrial melanism.  His research was conducted in two type of woodlands in England:  Birmingham (polluted) and Dorset (non-polluted; results are not presented in this paper ).  His great contribution is divided in two. Firstly, he coordinated surveys of the dark morphotypes across England, which was a country wide survey that allowed to establish a reference study for further studies of the species.  Secondly, he did provide evidence of bird feeding on peppered moths selectively.

2.Scope of this paper: To demonstrate experimentally (aviary and woodlands experiments) how color variation is under natural selection. Due to pollution generated during industrial revolution, dark morphos of Biston betularia (carbonaria and insularis) were assumed to be fitter that the white types (typical) because of lower predation during daytime.

3. Methodology

3.1 Field experiments: Experimental release in an industrial area

Mark- release capture experiments were conducted in polluted sites close to Birmingham. In this experiments only males were used. They were marked with a dots of paint.  The release occurred at  sundown. Two different types of trapping methods were used. In the fist, he used a trap made of perforated zinc, where only males were allowed to enter, but not escape. The second one used muslin cages.  One virgin female of each genotype (carbonaria, insularis and typical) was kept in each trap. Basically they did this because they wanted to keep as many males nearby the forest (female’s pheromones avoid males migration out the woodlands). Otherwise they would have escaped. Mark recapture was done using mercury vapor lights

3.2 Aviaries experiments

The aviary experiments were conducted in  Research Station , Madingley, Cambridge. Dark and light color trunks of different species were placed inside the aviary. The experiments used predators such as the Great Titis in order to measure predation upon the tree forms of bestularia, which were released inside the aviary

4. Results

4.1  Field experiments

Approximately 700 individual of the tree morphotypes were released.There was a large number of recaptures for the melanic forms (carbonaria and insularis). Assumption was that the white morphos (typical) could have been predated and that’s why there were not many recaptures.

4.2 Aviary experiments

For the very first time, selective elimination on incorrect background was first demonstrated. Therefore, the conclusion was that the birds are selective agents

 5. Conclusions

This study is the classical example of natural selection, which is explained in classical textbooks of evolutionary biology. The author spent a considerable part of his life studying the effect of industrial melanism on peppered moths. The results of the experiments supports the hypothesis that birds act as selective agents.

6. Question for discussing in class

1. Dark- melanic forms are less abundant in post-industrial Britain. Would you still consider the conclusions  presented by Kettlewell  well - founded? If you are supposed to measure the selection coefficient in nowadays. Do you think it will affect the conclusions presented by Kettlewell?

2. How about to take into account  other selective agents  than bird's predation, for example predation  by insectivorous bats of the genus Pipestrellus. How would the results differ from the ones already presented in the paper?