4.1 Biotic Interactions


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UBC Bio 111 - Intro to Biology

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4.1 Biotic Interactions

  1. 1. 4.1 Biotic Interactions Learning Outcomes 1. Identify different ways in which organisms interact and the outcomes of those interactions. 2. Distinguish among different types of predators. Readings: Chapter 14: 366-367, 370-378 Reminders: Reading quiz for Module 4 is due TODAY (before start of class) The learning centre has additional activities you have never seen to reinforce the key concepts for each week. At least 5 visits/over the semester will earn you 0.5% added onto your final grade. Although abiotic factors are important for determining where a species lives, biotic factors also have an important effect. Biotic factors are all the influences an organism faces from other living organisms such as what food it eats, what species preys on it, as well as what species competes with it within the same habitat. Under the forest canopy light can be limiting. These two species of ferns have spread their fronds to maximize the interception of light. Because they are growing closely together their fronds will overlap. Competing for light Below the surface of the soil, the root systems of plants seek out nutrients and water. Plant root forms range from fibrous and shallow to individual deep tap roots. The root systems from many individuals will intermingle. Competing for H20 & nutrients Hyenas and vultures both search the savannas for carrion (dead animals). Both species will feed on the carrion. Competing for food Blue mussels and barnacles inhabit the intertidal zone of marine shores. Both need to attach to the crowded rock surface. Competing for space Competition: Two species require the same resource that is in limited supply (Inter specific competition). They may actively interfere with each other or one may exploit the resource before the other competitor can access the resource. Competitive exclusion: The elimination of one competitor from the habitat by the successful acquisition of resources by the other competitor.
  2. 2. Garden snail (Pacific sideband snail) grazes vegetation using a file-like radula. Herbivory Leaf miners are the larvae of insects that eat the chlorophyll rich inner layer of leaves. Herbivory (Consumers only eat producers) Leeches attach to chordates, such as fish and non-hairy animals. They attach with a circular set of jaws to pierce the skin and draw out the blood. Parasitism obtains nutrients from an other organism by harming but not usually by killing them - Form of predation Sea gulls effectively hunt for food by searching the shallow waters and attacking live animals such as this sea star. Predation (Carnivory) Predation: The process of collecting, harvesting or hunting another organism (plants, algae, fungi, or animals) for consumption. A hummingbird feeds on nectar from a thistle flower. In the process the head of the bird is covered with pollen. The hummingbird is critical in the reproduction of the plant. Mutualism Lichens are formed from a sandwich of a blue green bacteria or algae between two layers of fungus. Both organisms are dependent on the other for survival. Symbiotic form of Mutualism b/c of close contact
  3. 3. Corals are animals that are encased in hard calcium carbonate shells. They consume other small organisms that they can catch with tentacles but also have algae embedded in their tissues that supply an extra source of energy through photosynthesis. Symbiotic form of Mutualism b/c of close contact Mychorrizal fungi are associated with the roots of plants. They provide an extensive network of hyphae (thread-like filaments) that absorb water and nutrients from a large area that they share in exchange for sugars from the photosynthetic plant. Very important association for plants in many soils (Similar stuff: rhizobium – bacteria. Capture N2 gas convert it into NO3 or NH4. These are usuable by plants) Symbiotic form of Mutualism b/c of close contact Mutualism: Individuals of two different species provide a benefit to each other. Symbiotic associations: Two mutualistic species are in intimate contact with each other, often not being able to survive without the other. Small fish like the damselfish often hide within crevices of coral to avoid predation by larger fish. The coral obtains no benefit from this interaction. Commensalism Individuals of one species benefit while there is no effect on the other species. Table of interactions – refer to your text to summarize the types of interactions Type of interaction Effect on Species 1 Effect on Species 2 + + Mutualism + - - Commensalism + Your Turn Identify the type of interactions illustrated (by pictures in class): 1. Squirrels eat mushrooms 2. 3. 4.
  4. 4. 5. 6. Please be prepared to answer questions about this case study in Monday’s class. You will be asked some of the questions given below as well as some related questions. Case Study: Temperature and competition determine habitat locations for three fish species living in mountain streams These fish species have been observed to live at different locations along Rocky Mt. streams. Salvelinus fontinalis Salmo trutta Semotilus atromaculatus brook trout brown trout creek chub high elevation middle elevations low elevations A study was performed by Taniguchi et al. 1998 which indicated that competitive abilities between the fish changed with temperature. An artificial large oval stream tank was used to test competition between the fish at different temperatures. Researchers could observe fish by watching them from the centre of the oval; also the tank mimicked a real stream by having sections with different depths and current speeds. Draw in layout of the tank as if looking at it from above. Competitive abilities were measured by number of aggressive acts (chasing and nipping other fish) and by the ability to successfully obtain food (floating invertebrates) compared to the other species. Besides the laboratory experiments, experimental field studies were also performed to study distribution of the three species in nature in streams of different temperature. The following figures indicate how many stream sites at a specific temperature contained the different species of fish. Brook trout alone QUESTION: 1. Describe the temperature ranges Brook and brown trout of tolerance for together each individual species based on this data.
  5. 5. Within the artificial stream for one replicate at a specific temperature one individual fish of each species was placed. All fish were similar sizes and had been previously acclimated to the temperature being tested. No brook trout were tested above 24oC because they did not survive acclimation above this temperature. For each temperature a number of replicates were performed. During each replicate the number of food items consumed by each fish was recorded (top graph) and the number of aggressive acts (bottom graph) was also recorded. QUESTIONS: 2. When you compare brook trout to brown trout are there any significant differences between the two species for how many food items they consume at different temperatures? 3. Describe food consumption by creek chum at different temperatures. When is it significantly less than the trout species? When is it not significantly different? Is it ever significantly higher than either of the trout species? The researchers wanted to know whether a particular species was consuming less food at a particular temperature due to the presence of a competitor or solely due to the particular temperature. After all 3 species had spent time together
  6. 6. at a particular temperature the fish which appeared to be the strongest competitor was removed. Then it was observed whether the remaining fish showed any increase in the number of food items consumed. QUESTIONS: 5. If food consumption increased after removal of the strong competitor what do you conclude was causing a fish of a particular species to eat less when the competitor was present? 6. Conversely, if food consumption did not increase after the removal of the competitor then what do you conclude? In the fig(a) for brook trout you can assume that the brown trout were removed and in the fig(b) for brown trout you can assume brook trout were removed. QUESTIONS: 7. Is brook trout inhibited by brown trout? Is there any influence of temperature on the results? 8. From 3-24oC was brown trout inhibited by brook trout? What can you conclude about the feeding behavior of brown trout at 26oC? 9. Do creek chub eat more when competitors are removed? In nature, brook trout are found in the highest elevation Rocky Mt. streams which tend to be the coldest. In this study they were found in the coldest temperature streams also. 10. Was there any significant difference in the amount of food they ate or in their competitive abilities at the lowest temperatures (3oC) tested compared to brown trout? 11. Why might they be found alone in the coldest (and highest) streams in nature then? 12. **Does temperature have an effect on competitive behaviour? Describe any significant differences in food consumption and aggressive behaviour below 20oC. 13. Did the creek chub ever have a competitive advantage over brook trout, if so at what temperature? 14. Did the creek chub ever have a competitive advantage over brown trout, if so at what temperature?
  7. 7. 15. ***What is your overall conclusion or conclusions from this study? Does temperature mediate competitive interactions between these species (and possibly effect patterns of species distribution in streams)? Trout dominate below 22 – 25 degrees. Because they are likely better adopted to the temperature allowing them to be better at obtaining food and have more aggressive behavior Trout experience thermal stress above this temp, whereas creek chub do not, and thus they will dominate. 16. What other factors may have an effect on where within a stream a species lives? Reference cited: Taniguchi, Y., Rahel, F.J., Novinger, D.C., and Gerow, K.G. 1998. Temperature mediation of competitive interactions among three fish species that replace each other along longitudinal stream gradients. Canadian Journal of Fish and Aquatic Sciences. 55: 1894-1901.