Paper 40: Effects of Forest Cutting and Herbicide Treatment

Paper 40: Effects of Forest Cutting and Herbicide Treatment on Nutrient Budgets in the Hubbard Brook Watershed-Ecosystem

Gene E. Likens et al. 1969

image source: http://www.hubbardbrook.org/overview/history.shtml 

Introduction:

The Hubbard Brook Forest is a great example of a long-term study through the Forest Service since 1955. This large-scale manipulation of an ecosystem aims to quantify biogeochemical and implications from changes in habitat or vegetation on an ecosystem level. Forest Service removed all vegetation from Watershed 2 in the Hubbard Brook Experimental Forest and sprayed herbicide to inhibit regrowth. 

Methods:

Precipitation and stream flow was measured using precipitation gauges and stream-guaging stations (V-notch weir and San Dimas flume). Weekly samples were collected plastic containers for chemical analysis. In November and December 1965, all vegetation was cut and left in place then the area was treated with Bromacil herbicide.

                                                                                                      

Hydorlogic Parameters:

Precipitation and stream flow were measured. Annual runoff showed a dramatic increase following the clear cut.

Precipitation Chemistry:

Most of the chemical input came from precipitation. Sulfate and hydrogen were abundant in rainfall and show, and pH was often less than 4.0. Soil and road dust are attributed for the metal ions. Nitrate increased every year of the study, and this is presumably because of air pollution.

Chemical Input Through Herbicide Application

Bromacil solution was sprayed on the watershed in 1966. There was 3,650 liters and Bromacil, and then 87 liters of ester was sprayed on the watershed in 1967. It is approximated that 0.7 kg Cl-/ha of chemical herbicide would be added into the water-shed.

Stream Parameters

Stream temperatures are relatively constant with an annual temperature of 16 degrees C. W2 stream temperatures increased post cut in the summer and winter. A thinker snow depth was noticed in the deforested area. Streams had discrete seasonal regimes (Figure 2). Dissolved oxygen was normal to slight above normal. Above normal dissolved oxygen is called supersaturation, and it is unknown why this occurred. Following treatment, W2 resulted in greater discharge, more turbulence, and a constant high level of dissolved oxygen. Increased turbidity is a direct result of erosion of the watershed, and a 4-fold increase in particulate matter that was increasingly inorganic. Hydrogen ion content increase 5-fold during the study, which is a significant decrease from 5.1 to 4.3 pH. Conductivity was variable in the stream water after treatment.

Ions

Undisturbed watersheds have low concentrations of ammonium ions with a season pattern and showed a reciprocal pattern in the treatment of W2. There is inconclusive evidence for nitrification. Sulfate concentration processes are complicated and decreased by 45% in the deforested W2. Chloride concentrations had a delayed increased in stream water by 65%. Calcium, magnesium, potassium and sodium are typically constant in undisturbed streams but were very high after treatment. Aluminum solubility was also increased as a result of a decrease in pH (10-fold increase in aluminum). Silica increased by 37%, probably as a result of wreathing of geologic substrate. Bicarbonate nearly dropped to zero after treatment.

Effect of Nitrification on Cation Loss

According to the data, nitrification is a major controlling factor in the quantity and quality of dissolved materials in the clear cut watershed, more so than an undisturbed watershed.

Nutrient Budgets

Net nutrient loss in the ecosystem was significantly increased after deforestation and herbicide treatment, and increased stream water concentrations were likely responsible.

General Discussion

Nutrient cycling is responsible for the retention of nutrients within an ecosystem. Disturbed systems can no longer can maintain the nutrient cycle, which results in a loss of nutrients.

Image source: http://www.hubbardbrook.org/6-12_education/Introduction/Intro1.htm

Questions:

Do you agree that turbidity has “little value” in the assessment of water quality? (p. 887)

How could this experiment be improved with modern technology?

Does this paper portray a realistic or idealized scenario?

How have forestry practices changed since this study? Have we learned from our mistakes?

Last question:
http://www.hubbardbrook.org/data/dataset_search.php
What do you think of the Hubbard Brook dataset?

http://www.hubbardbrook.org/overview/resphilos.shtml

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.