Ecology Exam 3 Answer Key (119 Questions)

EXAM 3: Ecology Exam 3 Study Guide 1. What is a scientific model? What are some advantages? A simplification or abstraction of a complex real-world problem.  Allows you to build hypotheses and predictions and explore outcomes  Helps to realize gaps and guide scientific inquiry 2. What is the equation for the logistic population growth model? dN/dt = rN(K-N/K) 3. What is the equation for the Lotka-Volterra Interspecific Competition Model? dN1/dt = r1N1((K1 – N1 – αN2) / K1) dN2/dt = r2N2((K2 – N2 – ßN1) / K2) 4. What does α12 stand for, and what is another way to write it? What about α21? Competition coefficient of species 2 on species 1. In other words, how much competition between 2 and 1 effects 1. You can also write α. 5. What is a zero isocline? How can you find the zero isocline? Lines that connect all combinations of densities of species 1 and 2 that result in zero population growth for either species 1 or species 2. To find the zero isocline for species 1, find the set of join densities that satisfy the equation 0 = K1 – N1 – αN2 6. Draw and describe the 4 different scenarios for the Lotka-Volterra models. 7. Given the following parameter values will species 1 and 2 coexist? Will one of the species be excluded? If so, which species? Species 1: N1 = 50, r1 = 0.1, K1 = 200 and α12 = 0.9 Species 2: N2 = 50, r2 = 0.2, K2 = 100 and α21 = 0.2 8. What is asymmetric interspecific competition? Where does it fall compared to symmetric competition and ammensalism? Are those -/-, +/-, etc. Asymmetric competition is where 1 species involved in the interaction is negatively affected to a much greater extent than the other species. It falls between symmetric competition and ammensalism. Symmetric competition is - / -, ammensalism is - / 0. 9. Why does population growth slow as the population reaches K? Give at least 3 reasons. 10. Explain the experimental evidence of asymmetric interspecific competition in cattails. One species was suppressing the other. When the suppressor was removed, the other’s range increased. 11. What is a mechanism of asymmetric competition in plants? Why is it asymmetrical? Competition for light. Taller plants get more light than shorter plants. 12. List 4 mechanisms of asymmetric competition in insects.  One species more efficient in exploiting the shared resource  Dominant species shows aggression toward subordinate  Subordinate species shows avoidance behavior  Dominant species modifies the habitat making it less hospitable to the subordinate 13. What are 3 +/- interactions? Describe them. Predation: individuals of 1 species (predator) kill and consume individuals of the other species (prey) Parasitism: individuals of 1 species (parasite) consume tissues of individuals of the other species (host), but without necessarily killing the host Herbivory: animals (herbivores) consume plant tissues 14. Why might herbivory have little or no effect upon the fitness of the plant that is being consumed? Plants can regrow their tissues lost to herbivores. 15. What is compensatory ability (tolerance)? The ability for a plant to regrow their tissues lost to herbivores. 16. How do plants achieve a high compensatory ability? List 3 ways. o Mobilize stored resources to fuel re-growth o Redirect resources that would have gone into storage to fuel re-growth o Increase photosynthetic rate of remaining undamaged tissue 17. How can insect herbivores suppress plant fitness? Laying eggs on the plant. The larvae eat the plant and may move to the next plant. 18. In a simple environment, what happens to prey when there are efficient predators? Contrast with a more complex environment. In simple environments, predators may consume prey to the point of extinction (and then they may also go extinct). In more complex environments, prey refuges may exist that allow prey to persist in spite of an efficient predator. 19. What are 4 types of prey refuges?  Spatial refuges: physical locations where prey are outside the reach of predators  Refuges in size: life-stages in which a prey species is unmanageable by a predator (usually too big)  Refuges in abundance: prey aggregations are either too numerous or too sparse for the predator to effectively hunt the prey  Refuges in dispersal ability: prey have superior dispersal ability to predators so they are always able to establish at least temporarily in locations where predators are absent 20. What happened in Huffaker’s experiment with herbivorous and predaceous mites? What was the take-home message? Herbivorous mites had superior dispersal ability which allowed them to persist through colonizing temporary refuges. 21. What is the “Ecology of fear”? Non-consumptive effects of predators on prey. Presence of predators alters prey behavior and these behavioral changes affect prey fitness. 22. How do predation and parasitism differ? Predation is killing, parasitism is not. 23. Describe the consequences of behavioral changes in elk and deer as a result of wolf reintroduction in Yellowstone NP. The prey acted differently and ruined the environment when the wolves were not around. 24. Presence of predators alters prey behavior and this affects prey fitness. 25. What are mutualisms? Interspecific interaction that increases the fitness of both species involved in the interaction. 26. What is facultative mutualism? A mutualism that is not essential to the survival of either species although it increases the fitness of both species. 27. What is obligate mutualism? A mutualism that is essential to the survival of both species. 28. The following questions refer to the mutualism between Acacia species and Pseudomyrmex ant species. A. What are 3 benefits to the ants?  Thorns that can readily be hollowed out and serve as a site for ant colony. o Domatium: chamber produced by plants within their tissues that can house arthropods.  Extrafloral nectaries: nectar-producing glands on parts of the plants other than the flowers.  Beltian bodies: protein-rich and lipid-rich packages derived from modified leaf tips. B. What are 2 benefits to the Acacias? o Deter invertebrate and vertebrate herbivores that would attack the plant. o Removal of competing vegetation. C. Enhanced performance of Acacias with ants is correlated with (higher/lower) densities of herbivorous arthropods. 29. Why are mutualisms in tropical systems often tighter (closer to obligate) than mutualisms in temperate systems (closer to facultative)? Temperate systems are more variable with the weather. NS favors more generalism (less specificity) in temperate climates vs. tropics, because of variability. 30. What is mycorrhizae and what are 2 types? Mutualism between the roots of plants and soil-dwelling fungi. Arbuscular mycorrhizal fungi: mycorrhizae in which the fungus penetrates and exists inside the cortical cells of the root. Ectomycorrhizae: mycorrhizae in which the fungus forms a sheath around the root and hyphae penetrate between, but not within root cortex cells. 31. How do the fungus and plant benefit in mycorrhizae? Fungus: access to carbohydrate-rich root exudates. Plant: greater uptake of soil nutrients that are relatively immobile, including P, Cu, and Zn; also a greater uptake of mobile nutrients and water. 32. One hypothesis for asymmetry in mycorrhizal mutualisms is that the degree of asymmetry in these associations is greater in nutrient-rich soils. Why? NS favors more aggressive fungi in these soils. 33. Fungi from nutrient-poor soils gave greater benefit to the plant. 34. What are some ways that an animal can cheat on the animal pollination mutualism? Nectar robbing, pollination by deceit 35. Why doesn’t NS favor greater ability to discriminate against non-rewarding plants in animal pollinators? List 2 reasons.  Fitness cost of being deceived is very small.  Fitness cost of passing up opportunities for rare resources (mates, oviposition sites) outweighs the fitness cost of being deceived. 36. What is a community? A collection of populations of all of the species that co-occur in a particular area at a particular point in time. 37. What are 3 ways of quantifying species composition of ecological communities? o Species richness o Species diversity o Species evenness 38. What is evenness? What is the equation and what do the variables stand for? A measure of how equally species are represented in the community. H/lnS H = diversity index S = species richness 39. Which community would be considered more diverse? 2nd one 40. What is the evenness in each of the above communities? DON’T need to do, because exam doesn’t allow calculators.  41. What is the 1st empirical pattern in communities? Most species in a community are moderately abundant, a few species are quite rare and a few species are quite abundant. 42. What is the 2nd empirical pattern in communities? Species diversity is higher in more complex environments. 43. What happens to species diversity in more complex environments? HIGHER. 44. What is the 3rd empirical pattern in communities? In plant and algal communities, species diversity DECREASES with INCREASING nutrient availability. 45. What happens to SD with increasing nutrient availability? Why does this happen? It DECREASES. May be because competitive exclusion principle (2 species can’t use same limited resource in same way). 46. Describe the Park Grass Experiment. Fertilized plots and unfertilized; checked species richness. 47. Over 95 years, species richness of plants in fertilized plots in the Park Grass Experiment (increased/decreased). 48. What is the 4th empirical pattern in communities? SD is highest in communities with intermediate levels of disturbance (maybe). 49. How does disturbance correlate with species diversity? HIGHER or LOWER disturbance: LESS SD. 50. What is the Intermediate disturbance hypothesis? SD is highest with intermediate disturbance. A. Explain this hypothesis tested in algal and invertebrate communities on boulders. Medium disturbance boulders had highest SD. i. Do small and large boulders have lower SD than intermediate-sized boulders? YES. 51. Answer the following questions about this rank-abundance (also called ‘dominancediversity’) curve. A. What is represented on the X-axis? Rank of species (most abundant  least abundant) B. What is represented on the Y-axis? Measure of representation of species in community (number of individuals, basal area) C. Approximately how many species occur in the coastal pond habitat? 18 D. Which community, mountain stream or coastal pond, has greater evenness of representation of species? 52. In a dominance-diversity curve, what would a steep line mean compared to one that is not as steep? Steep line means less evenness 53. What is a food web? A summary of who eats whom within a community. 54. What is a trophic level? A feeding level within a food web. 55. In general, do aquatic or terrestrial environments have more complex and higher-leveled food webs? Why? Aquatic 56. What are direct and indirect effects? Direct effect: effects of one species on another that are not mediated by an intermediary species. Indirect effect: effects of one species on another that are mediated by a 3rd intermediary species. 57. What is associational resistance (AR)? A prey species experiences less attacks by a shared predator where it occurs with an alternate prey species than where it occurs alone. 58. What is associational susceptibility (AS)? A prey species experiences more attacks by a shared predator where it occurs with an alternate prey species than where it occurs alone. 59. What is apparent competition (AC)? This is one step further than associational susceptibility. How is it different from it? Prey species suffers fitness consequences or less population growth, rather than just more attacks. 60. How does insect damage to a less-preferred host plant species vary in relation to the proximity and density of the preferred host plant species? Less-preferred may suffer AS (associational susceptibility) if more preferred makes the predator population increase. 61. What is oviposition and how does it damage plants? Lay eggs on plant and cover with protective cap. The larvae eat the plant and damage it. 62. Describe the experiment which compared number of R. conicus egg cases per wavyleaf thistle as a function of distance to the nearest musk thistle patch. (Wavyleaf was the lesspreferred plant for the insects). What happened? Wavyleaf close to thistle had more egg cases. A. Does this show associational susceptibility or apparent competition? Associational susceptibility because only damage was quantified. B. When the musk thistle co-occurred with the wavyleaf, was there greater or less attack? Greater. 63. Describe habitat restriction in the arctic hare. Is this an example of interspecific competition or apparent competition? Apparent competition. 64. Paine conducted research in a marine intertidal zone. What did he find? A. When the sea stars (predator) were removed, what happened to the species richness? Why? Less richness. Other species dominate. B. What happened to the species richness in the control, where sea stars were present? Why? Stayed the same. Population was controlled. 65. If you remove an herbivore that eats a competitively dominant species, then species diversity will (increase/decrease). 66. What happens when an herbivore consumes only the competitively subordinate species? Competitive dominant will take over. 67. Predator effects on species diversity of communities: A. A generalist predator: May promote species diversity – retard rate of competitive exclusion. B. A specialist predator that prefers the competitive dominant: May promote species diversity – retard rate of competitive exclusion. C. A specialist predator that prefers the competitive subordinate: May reduce species diversity – accelerate the rate of competitive exclusion. 68. What is frequency-dependent predation? The proportion of individuals of a species that are killed by a predator depends upon the abundance of the prey species relative to the other species in the community. 69. What is negative frequency-dependent predation? What does this do to species diversity? Most numerically dominant species suffers highest rate of predation; promotes species diversity. 70. What is a Keystone species? A species whose effect on the structure of a community is disproportional to its biomass in the community. 71. What is a Foundation species? A species that has a large effect upon community structure as a result of its large biomass in the community. 72. What is primary (1º) productivity? Rate at which energy is converted by producer organisms into organic compounds. A. Gross 1º productivity Rate at which radiant energy is fixed by photosynthesis by produced organisms; total rate of photosynthesis (NPP + Respiration). B. Net 1º productivity Rate of storage of organic matter in plant tissues exceeding the respiratory use by the plants; rate of production of new plant tissues. C. Net community productivity Rate of storage of organic matter by autotrophs that is not consumed by heterotrophs. D. Standing crop biomass Weight of living biological materials in a particular location at a specific time. 73. Variation in NPP among biomes is predicted by evapotranspiration, a function of precipitation and temperature. 74. Which biome has the highest NPP? Lowest? Tropical rainforest; desert and tundra. 75. What is an estuary? Is there a high/low nutrient input? River meets ocean; high 76. Do algal reefs and coral reefs have high or low NPP? 77. Does the open ocean have high or low NPP? 78. 1º production in grassland (increases/decreases) with greater annual precipitation. 79. What are 3 factors explaining NPP variation at smaller spatial scales? 1. Nutrient availability 2. Diversity of plant species in the community 3. Herbivory by large herbivores. 80. Describe a nutrient manipulation experiment. Demonstrate the important of nutrients to determining NPP. 81. In dry alpine tundra, what nutrient(s) were the limiting factor(s)? What about wet tundra? Dry – N; wet – N and P 82. In a grassland community, there are 5 plots which receive the same number of seeds. However, in the plots with a greater number of species, what can we expect of the NPP? Greater NPP. 83. Why does NPP increase with species richness? Maybe the niches are differentiated in such a way that their performance is less restricted by interspecific, rather than intraspecific, competition. 84. What is niche complementarity? Certain combinations of species seem to facilitate one another compared to their performance with other members of their own species. 85. In Serengeti grasslands, what happened to NPP when wildebeest didn’t graze? Lower NPP where wildebeest did not graze. 86. Why might grazing stimulate NPP? List 3 reasons. Removal of biomass by grazers may: 1. Reduce the amount of respiring tissue, so more E can go to biomass production. 2. Reduce self-shading, remaining tissue has more access to light, allowing more photosynthesis. 3. Change light quality (red : far red ratio) such that grasses are stimulated to ‘tiller’: produce new modules asexually 87. Highest levels of NPP may occur at (high/intermed/low) grazing intensies. 88. As a review, list and describe 3 empirical patterns in communities. More complex has more SD Intermediate levels of disturbance have higher SD Algal and plant communities have less SD with more nutrients 89. What is secondary (2º) productivity? Does this pertain to autotrophs or heterotrophs? Rate at which heterotrophs in an ecosystem produce new biomass 90. What is ecological efficiency? Ratio between energy flow at different points in the food chain 91. What is trophic level transfer efficiency and the formula? What is the mean and the common range? Why is the mean so low? The proportion of E at one trophic level that is present at the next higher trophic level. 10% mean (2-24%); because not all E gets ingested or used to produce new biomass. 92. What is consumption efficiency (CE) and what is the formula? (Explain the variables). Proportion of E in biomass produced at a higher trophic level that is consumed at the next higher trophic level. It/Pt-1 x 100 93. Compare CE in carnivores vs. herbivores. Greater in carnivores. 94. Do aquatic or terrestrial plants have greater CE and why? Aquatic; aquatic plants are often more appealing and don’t contain lignin. 95. What is assimilation efficiency (AE)? What is the formula? Proportion of E ingested at a trophic level that is assimilated at that trophic level. At/It x 100 96. What is production efficiency (PE) and the formula? Proportion of E assimilated at a trophic level that is incorporated into new biomass produced at that trophic level. Pt/At x 100 97. What are 2 factors affecting production efficiencies in animals? 1. Ectothermy vs Endothermy 2. Body size 98. Do ectotherms or endotherms have greater PE and why? Ectotherms have greater production efficiency (PE); endotherms use their E for things that ectotherms aren’t. 99. Greater body size means (greater/smaller) PE. 100. How do PE’s compare for different groups of animals? Invertebrates, ectothermic vertebrates, and endothermic vertebrates. Greatest in invertebrates; 2nd ecothermic vertebrates; 3rd endothermic vertebrates 101. What is the ¾ Power Law? Metabolic rate of an individual animal tends to increase as the ¾ power of its weight. 102. Why are predators relatively rare? Little E flows up to top of food web. 103. What is the pyramid of biomass? Because of low trophic level transfer efficiency, little E filters up to high trophic levels, so little biomass can be supported at high trophic levels. 104. What are biogeochemical cycles? Cycling of chemical elements between living and non-living components of the ecosphere. 105. What is a nutrient cycle? A biogeochemical cycle in which the chemical element is required by livin organisms. A. What is a gaseous-type nutrient cycle? A nutrient cycle in which the most accessible large pool of the nutrient is the atmosphere. B. What is a sedimentary-type nutrient cycle? A nutrient cycle in which the most accessible large pool of the nutrient is rocks. 106. What is a flux? Moves nutrients from 1 place to another (photosynthesis, erosion, etc.) 107. List and describe 3 ways that chemical elements in the atmosphere become available to living organisms. 1. Absorption by organisms 2. Wetfall – deposited to earth in precipitation 3. Dryfall – settling of small particles and aerosols without precipitation 108. Compare rain-out to wash-out. Components of wetfall; rain-out: particles form nuclei of raindrop; wash-out: raindrops pick up particles as they fall to the earth 109. List and describe 2 ways that chemical elements in the lithosphere become available to living organisms. 1. Mechanical weathering – physical breaking of rock into smaller pieces by action of freezing, abrasion by wind, cracking by plant roots 2. Chemical weathering – chemical reactions that release elements in minerals in bedrock 110. Global Nitrogen Cycle A. Where is the largest pool of N? Atmosphere B. This is a gaseous or sedimentary cycle? C. What form does N usually exist in? Is it directly available for use by most organisms? N2; not usually D. What is N fixation? Process of converting gaseous N2 into ammonia, which can readily be converted into forms useable by plants. E. What is nitrification? Conversion on ammonium in the soil into nitrites and nitrates by nitrifying bacteria. F. What is denitrification? Conversion of nitrites into gaseous N2 by heterotrophic bacteria. G. What is a way that humans throw off the Global N Cycle? Burning forests 111. Global Phosphorous Cycle A. P limits NPP in (aquatic/terrestrial) ecosystems. B. Is this a gaseous or sedimentary cycle? C. Where is the largest pool of P? Sediments at bottom of ocean D. Where are sources of P on land? Poop of birds that each sea fish; washed up dead aquatic organisms E. How do humans throw off the cycle? Mine P for fertilizer F. What is eutrophication? Process of nutrient enrichment in aquatic ecosystems resulting in great 1º productivity. 112. Global Carbon Cycle A. Where are a few places where C is on earth? Dissolved in oceans, tied up in rock, hydrocarbon deposits (oil, etc.) B. Where is C most accessible? Atmosphere C. Is this a gaseous or sedimentary cycle? D. What are 2 ways that C is exchanged? Photosynthesis, respiration E. Draw an example of the C cycle in an ocean. F. How do humans affect the cycle? Pollution, adding methane (CH4) G. How is an increase in C harmful? Reduces photosynthetic capacity; holds infrared radiation, blanket trapping heat 113. Global Hydrological Cycle A. Where are the 3 main pools of water? Ocean, glaciers, groundwater B. What are 2 methods of exchange? Evaporation and transpiration C. What is groundwater? H2O in cracks and fissures in rock D. What is evapotranspiration? Total movement of water into the atmosphere through both evaporation and transpiration E. Is evaporation or precipitation more prevalent? F. What is an aquifer? Is water in aquifers renewable? Porous underground strata of rock, usually composed of limestone, sand and gravel that is bounded above and below by impervious rock or clay; nonrenewable G. How do humans affect the cycle? Increase rates of runoff; deforesting; using water in aquifers 114. What is mineralization? Conversion of chemical elements from organic form into inorganic form; a process that occurs during decomposition 115. What is immobilization? Conversion of a chemical element from inorganic form into organic form; a process that occurs as a part of producers and decomposers building biomass 116. What is leaching? Loss of water-soluble plant nutrients from soil because they are carried away or to depths beyond the reach of plant roots by water flowing through the soil. 117. What type of bacteria carry out mineralization? Ammonifying bacteria 118. What is a phreatophyte? Deep-rooted plants that take up water from the zone of saturation in the soil or underlying rock, or the layer immediately above it. 119. Lotka-Volterra problems A. Use the following info and the Lotka-Volterra model of interspecific competition to predict whether species 1 and species 2 will coexist or whether one species will be competitively excluded. If the model predicts that one species will be competitively excluded identify which species will be excluded. Species 1: N1 = 850, r1 = 0.1, K1 = 1000, α = 1.6 Species 2: N2 = 50, r2 = 0.2, K2 = 700, ß = 0.9 Species 1 excludes species 2 B. Determine whether species 1 and species 2 will coexist or whether one of the species will be competitively excluded. If one species will be competitively excluded then identify which species will be competitively excluded. Scenario 1: N1 = 100, r1 = 0.2, K1 = 300, α12 = 0.3 N2 = 500, r2 = 0.4, K2 = 400, α21 = 0.5 Coexist Scenario 2: Use the same values except for changing K2 = 75 Species 1 excludes species 2