Matt Nauman

Cory Padilla

3/16/09

54/80

Post-settlement Competition In Damselfishes

4/4Coral reefs are amazing ecosystems that offer a great chance to explore the mechanisms behind systems of high diversity. Understanding the dynamics of coral reefs is a giant leap towards understanding the very foundations of diversity. The Great Barrier Reef off of northeast Australia alone is estimated to hold upwards of 2,600 species of shore fishes (Randall, 1), not to mention the huge populations of invertebrates that live there and migratory fishes that pass through. Several different processes work together on these reefs to result in such high diversity, most notably, predation, competition, and disturbance.

In our study we will look at interspecific competition’s effects on diversity. In general, competition is driven by the need for a limited resource (space, food, shelter…). Competition can take place on two levels, either interspecific (different spp.), or intraspecfic (within the same spp.). Competition is an important factor in the ecology of all ecosystems, and many studies about competition and its effects have been highly debated due to different interpretations (Roughgarden, 1983). In our study, we will consider the works of Peter Sale an ecologist who has done extensive research on the reefs in northwestern Australia. Through his studies of these damselfishes he concluded that these fish fallow the lottery hypothesis. The Lottery Hypothesis assumes that a system is competition based, meaning that a resource (space, food, shelter) limits the carrying capacity of the system. For that resource, the larval pool is saturated meaning the second that the resource opens (death) it will be filled. In the coral reef system the limiting resource is space. Lottery also assumes that all competitors must be equal with an equal abundance of larvae so that there is no resource partitioning (sharing), and that all competitors must have an equal probability of settling from the larval pool. Therefore, according to these assumptions, the likelihood of acquiring the resource (in our case space) is due to random chance, i.e. being at the right spot when someone dies. If all these assumptions are true, the lottery hypothesis predicts that the total abundance will remain just below carrying capacity, and that relative abundance of species fluctuates randomly. (Figure 1)

Figure 1. Shows how the Lottery Hypothesis looks with proportional abundance fluctuating while the total abundance is right below carrying capacity. (Carr)

When Sale ran experiments on three different species of Damselfish, P.wardi, E.apicalis, and P.lachrymates he failed to refute the lottery hypothesis, (1977, 1978). However, another scientist, Peter Doherty ran an experiment on the same species of damselfish (1983) and rejected the lottery hypothesis. Doherty interpreted from his data that one of the three tested species of damselfish; P.wardi was a more dominant competitor than the other two species, violating a critical assumption of the lottery hypothesis.

A key step towards verifying that the lottery hypothesis is driving the species diversity in this situation is to show whether these damselfish are equal competitors, or not. In order to quantify this process, we will classify two types of competition, symmetric, and asymmetric. Symmetric competition will mean that the negative effect on each species is equal and therefore competition is equal. Asymmetric competition will mean that the negative effect of one species is greater than the negative effect on the others, leading to unequal competition (species dominance). Because P.wardi, E.apicalis, and P.lachrymates have large population sizes, competition at the individual level will be highly variable within each species and therefore will be difficult to see results from. The best way to determine whether competition is symmetrical or asymmetrical will be to observe broader population level competition, such as mean abundance over time.

2/2The pattern observed is taken from Peter Sale’s 1978 Coexistence of Coral Reef Fishes-a lottery for living space. The pattern is: populations of three species of damselfishes;Pomacenturs wardi, Plectroglyphidodon lacrymatus, andEupomacentrus Apicalis are randomly distributed over reef areas (figure 2). Wherever there is coral rubble at a site, nearly all of the open space is taken up by these fish, and that the fishes are equal competitors in their ability to settle and maintain a site (figure 3)

Figure 2. Shows the where these three species settled (on coral rubble), and the territories they hold (Sale 1978).

Figure 3. Shows the mean relative abundance over time as been symmetrical. 4/4

The goal of our experiment is to examine post-settlement competition in damselfishes P.wardi, E.apicalis, and P.lachrymates. We will compare interspecific competition by looking at the mean relative abundance of populations after many simulated generations. The results of our experiments will show what type of competition is occurring within these three common species and will either confirm or deny a key assumption of Sale’s lottery hypothesis. Also, if competition is shown to be asymmetrical then our experiment will show which of the three species P.wardi, E.apicalis, and P.lachrymates is the dominant competitor. The second part of our goal is to see how the introduction of a predator will effect interspecific competition. An interesting possibility, is that the system without predators could be asymmetric competition with one species identified as a dominate competitor, but with the introduction of a predator the mean relative abundance will shift to be symmetric, drawing a bridge between Sale and Doherty’s different conclusions

4/4The fish being tested here are the same fish that both Sale, and Doherty used in their experiments:Pomacenturs wardi, Plectroglyphidodon lacrymatus, andEupomacentrus Apicalis. All these species of damselfishes occur in the South Pacific Ocean, mainly on reef systems of the northwestern coast of Australia (Randall, 346). In these warm temperate waters the temperature is at 25.5 C, pH is 8.2, water hardness or dKH (CaCO3 concentration) is 11 (Randall, 346). These three damselfishes occur most frequently on cresting reefs (Sale 1978)(Figure 4). The main substrate on these crests is coral rubble, made of broken pieces of coral, mostly acropora (Teresa Zubi). As Sale, observed, the main limiting resource among these fishes is space. P.wardi, E.apicalis, and P.lachrymates are territorial over plots of substrate, which tend to be a little less than a meter square (Gibson, 361). They utilize these meter sized plots to grow epithlic algae on which they graze (Klumpp, 1987). According to Sale, the competition these fish exhibit is for these territories in which they cultivate their own epithlic algae.

Figure 4. Shows that P.wardi, E.apicalis, and P.lachrymates (the top three) all occur on reef crests (Sale, 1978)

4/4We will run these tests in a lab setting, in a large aquarium. The dimensions of the tanks will be: ten meter long by five meters wide by three meters deep. This will yield fifty square meters of surface area. Since these damselfishes hold territories of about one meter each, this bring the carrying capacity of the tank to roughly fifty individuals. The substrate will be coral rubble, mainly acropora, and will be distributed evenly and level to ground, making a homogeneous environment. The water parameters will be maintained through extensive biological filtration to simulate the same water quality as in the South Pacific. Phosphates, carbon dioxide, oxygen levels will be maintained at a reasonable level along with adequate lighting to support epithlic algae, to provide food. Water quality will be monitored daily to ensure optimum conditions.

Our first experiment will test whether P.wardi, E.apicalis, and P.lachrymates are symmetrical competitors post-settlement, or whether one species is competitively superior or inferior to the other two, showing asymmetrical competition. We plan on testing this general hypothesis with two alternative specific hypotheses. There are two alternative hypotheses rather than a null hypothesis because, there are only two possible test results: either the damselfish will compete symmetrically and will have equal relative abundances, or they will compete asymmetrically and will have varying relative abundances.

General Hypothesis: Post-settlement competition between three damselfishes E. apicalis, P. wardi, and P. lachrymates is symmetrical (or not)

Alternative Specific Hypothesis #1: If we introduce an overabundance of larvae of the three species in equal amounts to a predator free environment with limited resources, and record abundances after 2 months, then after 15 repetitions the mean proportions of the three species will be approximately equal, showing symmetrical competition.

Alternative Specific Hypothesis #2: If we introduce an overabundance of larvae of the three species in equal amounts to a predator free environment with limited resources, and record abundances after 2 months, then after 15 repetitions the mean proportions of the three species will not be equal, showing asymmetrical competition.

As you can see from the hypotheses there is no need for a null hypothesis because the rejection of one hypothesis leads to the validation of the other, and vise versa.

To test our hypotheses we plan on using a large aquarium setup. We will build a 10m long x 5m wide x 3m deep aquarium to house our tests, this should provide space for about 50 fish to live because they each require approx 1m to survive. We will completely cover the bottom in a substrate of crushed coral, simulating the reef crest area (preferred depth and substrate) that these fish prefer to settle on and we will match the water parameters to the water conditions from where these fish live in northwest Australia (T=25.5° C, Ph=8.2, dKH=11°). We will also maintain the epithilic algae so there is plenty of food.

As a control we will test to see if each of the three species can survive and flourish in our tank. We will fill the tank 100+ larvae of P.wardi and observe to test if the fish fill the tank to its carrying capacity. We will then replicate the control using the other two species of damselfish E.apicalis, and P.lachrymates.

Assuming our control experiments all go well and all three species of fish survive in our tank then we will proceed on to our actual experiments. In our first hypothesis we are testing whether P.wardi, E.apicalis and P.lachrymates are equal competitors, so, we will fill the tank with an overabundance of larvae, (100 of each species), and plenty of food so the limiting resource is space. We will observe the larvae for two months as they grow and compete with each other, after two months we will take out all of the species and count how many of each species there are, this will give us the relative abundance of each of the species. We will then remove all the larvae from the water and the tank and repeat. We will do 15 trials and afterwards calculate the mean relative abundance for each species. If competition is symmetrical then there should be different relative abundances for each trial, but over many trials the overall number of each species should be about even, making the mean relative abundance about equal and rejecting alternative hypothesis #2. If competition is asymmetrical, a pattern should arise where one species’ abundance is consistently different from the others rejecting alternative hypothesis #1.

Second, we want to test, based on our results from our first experiments, how/whether adding predators to the system will affect the relative abundances. Again we are going to be using alternative specific hypotheses rather than having any nulls because the results of each of our tests will either support or refute the others.

General Hypothesis 2: The introduction of a predator(s) will cause a shift in mean relative abundance (or not).

Alternative Specific Hypotheses #3 and #4 are assuming that the results of our first experiment showed that P.wardi, E.apicalis, and P.lachrymates compete symmetrically:

Alternative Specific Hypothesis #3: If we introduce a predator to the system described in Specific Hypothesis #1 then the mean relative abundance of the system will remain approximately equal and imply that the introduction of a predator has an equal effect on all 3 species.

Alternative Specific Hypothesis #4: If we introduce a predator to the system described in Specific Hypothesis #1 then the mean relative abundance of the system will shift from being equal (symmetrical competition) to unequal (asymmetrical competition) and imply that the introduction of the predator has an uneven effect on the three species.

Alternative Specific Hypotheses #5, #6 and #7 are assuming that the results of our first experiment showed that P.wardi, E.apicalis, and P.lachrymates compete asymmetrically.

Alternative Specific Hypothesis #5: If we introduce a predator to the system described in Specific Hypothesis #2 then the mean relative abundance of the system will shift from being unequal (asymmetrical competition) to being equal (symmetrical competition) showing that the predators have an unequal effect on the three species, but, are the factor that keeps the species approximately equal.

Alternative Specific Hypothesis #6: If we introduce a predator to the system described in Specific Hypothesis #2 then the mean relative abundance of the system will remain unequal and unchanged (asymmetrical competition) showing that predators have an equal effect on the three species.

Alternative Specific Hypothesis #7: If we introduce a predator to the system described in Specific Hypothesis #2 then the mean relative abundance of the system will shift from one arrangement of inequality i.e. (60% -30%-10%) to another (27%-17%-56%), implying that predators have an uneven effect on the three species.

To test our second general hypothesis and specific hypotheses, we will a near identical setup to the first experiment. We will use the same tank, (10m x 5m x 3m) with the entire bottom covered in a crushed coral substrate, we will maintain epithilic algae so there is plenty of food, the water parameters will again be 25.5°C, Ph=8.2, and dKH =11°, matching those of our species’ habitat, and we can assume that the results of the control experiment will be the same as they were the first time, so we know that none of the species will fail to survive due to the tank/water.

To study the effect of predators on the competition of damselfish, we will again over saturate the larval pool of our tank with 100 larvae of each P.wardi, E.apicalis, and P.lachrymates. To test the effect of predation, we will add 5 adult Coral Groupers (Cephalopholis miniata) a predator of the damselfish, to the tank as well. We will let the fish live in the aquarium for 2 months and at the end of the 2 months we will count how many of each species there are living in the tank. We will clean out the tank and repeat, until we have a total of 15 trials, at the end we will average the relative abundances to find the mean relative abundance. Assuming the first experiment showed competition to be symmetrical our two hypotheses are: #1. Our mean relative abundances should stay the same (predators have an equal effect on all species and competition stays symmetrical). #2. Mean relative abundances should change (predators have an unequal effect on the three species, make competition asymmetrical). If our first experiment showed that predation is asymmetrical there are 3 options. #1 mean relative abundances could shift to equality (showing that predation evens out otherwise uneven competition between the three damselfish). 2. Relative abundances could stay the same between the three fish, showing that predation has an equal effect on all three species (competition stays asymmetrical). Or 3. Mean relative abundances will shift, but not to equality, showing that predation has an effect on the survival of the damselfish, but it is not the effect we anticipated.

Our experiment will be conducted in a lab setting; we realize this eliminates countless factors affecting competition. Disturbances, potentially patchy larval abundances, heterogeneous substrates, outside competition, and other predation are all important influences on competition, however, they must be removed from our tests to accurately hone in on the competition within these three species. Hopefully our test will provide a clearer window in important factor in the maintenance of diversity.

Works Cited

Carr, Mark. “Community Ecology Review.” 20 Jan. 2009.

- - -. “Maintance of Diversity-2.” 26 Feb. 2009.

Connell, Joseph H. “Diveristy in Tropical Rain Forest and Coral Reefs.” Science, New Series 199.4335 (1978): 1302-1310.

Doherty, Peter J. “Tropical Territorial Damselfishes: Is Density Limited by Agression or Recruitment .” Ecology 64.1 (1983): 176-190.

Doherty, Peter J, and David McB Williams. “The Replenishment of Coral Reef Fish Populations.” Oceanography and Marine Biology (1988): 487-551.

“Dr. Peter Sale.” Univerity of Windsor. 22 June 2007. University of Windsor. 9 Mar. 2009 <

Klumpp, D. W., D McKinnon, and P. Daniel. “Damselfish territories:zones of high productivity on coral reefs.” Marine Ecology 40 (Oct. 1987): 41-51.

Randall, John E. Reef and Shore Fishes of the South Pcifica: New Caledonia to Tahiti and Pitcairn Island. Honolulu: University of Hawai’i , 2005.

Roughgarden, Jonathan. “Competiton and Theory in Community Ecology.” American Naturalist 122.5 (1983): 583-601.

Sale, Peter F. “Coexistence of coral reef fishes - a lottery for living space*.” School of Biological Sciences, The University of Sydney 3.1 (1978): 85-102.

- - -. The Ecology of Coral Reef Fishes. N.p.: Academic Press, 1993.

Zubi, Teresa. “Ecology Coral Reefs.” Coral Reefs (Reefs on earth, types of reefs, morphology). 6 Apr. 2008. Starfish channel. 6 Mar. 2009 <

Graph of predicted results 0/5 per hypo