IB Biology HL 1-2: C 4.1 Communities PDF

C 4.1 Communities C.4.1.9 - C.4.1.18 IB Biology HL 1-2 C 4.1.9 A community is all of the interacting organisms in an ecosystem Community: Several populations living and interacting with each other C 4.1.10 Competition versus cooperation in intraspecific relationships Intraspecific relation...

C 4.1 Communities C.4.1.9 - C.4.1.18 IB Biology HL 1-2 C 4.1.9 A community is all of the interacting organisms in an ecosystem Community: Several populations living and interacting with each other C 4.1.10 Competition versus cooperation in intraspecific relationships Intraspecific relationship: relationship between individuals of the same species 1. Competition Occupy the same ecological niche Examples Plants: competing for light, pollinators or soil nutrients. Animals: Competing for food, territory or mates Leads to natural selection because some individuals will have traits that help them outcompete others. C 4.1.10 Competition versus cooperation in intraspecific relationships Intraspecific relationship: relationship between individuals of the same species 1. Cooperation Mutually beneficial relationships Examples Huddling together to stay warm Hunting in groups Defenses against predators C 4.1.11 Herbivory, predation, interspecific competition, mutualism, parasitism and pathogenicity as categories of interspecific relationships within communities Interspecific relationships: relationships between different species (6 types) 1. Herbivory: primary consumers eating primary producers May or may not kill the producer Examples Sheep eating grass Aphids eating sap from phloem Snails eating algae C 4.1.11 Herbivory, predation, interspecific competition, mutualism, parasitism and pathogenicity as categories of interspecific relationships within communities Interspecific relationships: relationships between different species (6 types) 2. Predation: one species kills and eats another species Predator-prey relationship Examples Hawk eating a mouse Dolphin eating a fish Ladybug eating an aphid C 4.1.11 Herbivory, predation, interspecific competition, mutualism, parasitism and pathogenicity as categories of interspecific relationships within communities Interspecific relationships: relationships between different species (6 types) 3. Interspecific competition: two different species competing for the same resource Examples Different species of barnacles competing for space on a rock Ivy climbing up an oak tree to compete for light Cheetahs and lions competing for the same prey C 4.1.11 Herbivory, predation, interspecific competition, mutualism, parasitism and pathogenicity as categories of interspecific relationships within communities Interspecific relationships: relationships between different species (6 types) 4. Mutualism: two different species both benefiting from each other Examples Mycorrhizal fungi on plant roots Algae and corals Mutualistic pollinators C 4.1.11 Herbivory, predation, interspecific competition, mutualism, parasitism and pathogenicity as categories of interspecific relationships within communities Interspecific relationships: relationships between different species (6 types) 4. Parasitism: a parasite lives in/on the host Parasites benefit and the host is harmed Examples Ticks living on deer Tapeworms living inside a blue whale Giant padma plants living off nutrient in vine roots C 4.1.11 Herbivory, predation, interspecific competition, mutualism, parasitism and pathogenicity as categories of interspecific relationships within communities Interspecific relationships: relationships between different species (6 types) 4. Pathogenicity: a pathogen lives inside a host Causes a disease Examples Tuberculosis bacteria in badgers HIV in humans Potato blight fungus C 4.1.12 Mutualism as an interspecific relationship that benefits both species Mutualism: Two different species, both benefit Usually from two different kingdoms as they bring very different things into the relationship (3 examples) 1. Root nodules in Fabaceae Fabaceae plants (peas) develop nodules that protect the bacteria from consumers. The plant also provides carbohydrates for the bacteria to use as an energy source. Rhizobium bacteria absorb and fix nitrogen, helping the plant avoid nitrogen deficiency and giving it an advantage over other plants. C 4.1.12 Mutualism as an interspecific relationship that benefits both species Mutualism: Two different species, both benefit Usually from two different kingdoms as they bring very different things into the relationship (3 examples) 2. Mycorrhizae in orchids Orchids provide carbohydrates from photosynthesis for the fungus to use as an energy source. Fungus absorbs and supplies nutrient form the soil that the plant needs (water, nitrogen, phosphorus). C 4.1.12 Mutualism as an interspecific relationship that benefits both species Mutualism: Two different species, both benefit Usually from two different kingdoms as they bring very different things into the relationship (3 examples) 3. Zooxanthellae in hard corals Coral provides a protected environment close to the surface where the algae can absorb light, and also carbon dioxide from respiration. Zooxanthellae algae provide carbohydrates and oxygen to the coral from photosynthesis. C 4.1.13 Resource competition between endemic and invasive species Endemic species: occur naturally in an area Alien species: introduced outside their range by human activity Invasive species: alien species that spread rapidly due to the lack of density-dependent factors like natural predators Invasive species are often able to out-compete endemic species Endemic species occupies a smaller niche, declining in number or going extinct Example: Red lionfish in the caribbean C 4.1.14 Tests for interspecific competition Chi-square test for species association Random quadrat sampling A B A&B H0 → two species distributed independently H1 → two species are associated Rejection of the null hypothesis does not necessarily mean they are competing. Further investigation needed (field manipulation, mesocosms, laboratory experiment) Experimental vs. observational studies. C4.1.15 Use of chi-squared test for association between two species Expected = row total x column total Observed grand total Species A Species A Row total Species A Species A Row total present absent present absent Species B 45 3 Species B (48 x 51)/85 (48 x 34)/85 48 = 28.8 48 present present = 19.2 Species B 6 31 Species B (51 x 37)/85 (34 x 37)/85 absent 37 absent = 22.2 = 14.8 37 Column Column 51 34 85 51 34 85 total total C4.1.15 Use of chi-squared test for association between two species Calculating X2 (Chi-squared) O = Observed E = Expected Both A present B present Both present B absent A absent absent Observed 45 6 3 31 Expected 28.8 22.2 19.2 14.8 [(O-E)2]/E 9.11 11.82 13.67 17.73 X2 (Chi-squared) = 9.11 + 11.82 + 13.67 + 17.73 = 52.33 C4.1.15 Use of chi-squared test for association between two species 2 Calculated 𝛸 = 52.33 Degrees of freedom: (# of row - 1) x (number of columns -1) Critical value p = 0.05 If the calculated chi-squared value is greater than the critical value in the table, then we reject the null hypothesis (there is an association between species) C 4.1.16 Predator-prey relationships as an example of density-dependent control of animal populations Predator-prey cycles Prey = food for predators = predators Predators = predation = prey Prey = food for predators = predators Predators = predation = prey C 4.1.17 Top-down and bottom up control of populations in communities. Top-down: something from higher in the food chain affects a lower level Predators (predation) Herbivores Bottom-up: something from lower level affects a higher one (nutrient Producers sources) Both can happen, but one will be Nutrients dominant. C 4.1.18 Allelopathy and secretion of antibiotics Metabolic pathways are common to most organisms, but some are unique. Targeting a metabolic pathway unique to a certain group can control that population. Antibiotics are secreted by microorganisms to kill other microorganisms Penicillium fungi secrete antibiotics that weaken bacterial cell walls Allelopathic agents: secreted by plants into the soil to kill other plants Ailanthus altissima releases a plant-killing chemical and has become an invasive species. C 4.1.18 Allelopathy and secretion of antibiotics