Article Summaries for BIO120 (14-22)

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University of Toronto St. George
Paul Thompson

14 – community ecology  Ecological community: group of interacting species that live in the same area. Bound together by the environment and their interactions with each other  Keystone species: species that has a larger effect on their community relative to their abundance 15 – resource partitioning and why it matters  Interspecific competition versus intraspecific competition  Coexistence is impossible between two species that use the resource in the exact same way  Species can share resources and reduce interspecific competition by differing in what they consume - E.g. Species of bumblebees in colorado compete for flower nectar, but each species has preferred flowers based on the length of their corolla - In plants, coexisting species have different ways of obtaining nitrogen  Species that use resources in the same way will not forage in the same area, species that forage in the same area will not use resources the same way - E.g. Tree dwelling lizards – if they like the same branch thickness, they ate different sized prey  If intraspecific competition > interspecific competition, there will be no competitive exclusion - I.e. Species must limit their own population more than population of other species  Competition drives species to evolve towards partitioning resources - E.g. Darwin’s species of finches – they differ in bill shape/size when found together than when separate  Loss of high partitioning species = loss of certain resources in ecological group - E.g. Loss of grass specialized in4nh use means loss of4nh nutrient  Resource partitioning makes ecosystems sensitive to extinction 16 – predation, herbivory, and parasitism  All are examples of antagonistic interaction, where one party benefits while to the other is detrimental  Antagonistic interactions maintain population sizes Predation  Influences organisms at community (# of individuals in a population) and individual (fitness) level - E.g. Lion eating deer, or even ants eating seeds (all are carnivorous interactions) - Venus fly trap, and protozoa and bacteria are also considered carnivorous  Traits that aid predators for predators, and aid escape for prey, are selected by natural selection - Predator-prey arms race : both get better and better  Predators have traits such as claws, teeth, and sensory organs to help them catch prey  Prey have traits like camouflage, bright colours, and decoys for escaping  Some species have bright colouration to signal to predators that they are toxic - Toxins either manufactured by body or acquired via consumption of plants - Some species mimic colour and pattern of toxic species Herbivory  Plants have evolved defenses, and herbivores have evolved adaptations to obtain best nutrients - Herbivore-plants arms race Parasitism  Parasites consume nutrients from the host and decreases the fitness of the host  Pathogens are disease causing parasites  Endoparasites live inside the body while ectoparasites live outside the body  Parasitoids kill the host, but are not predators because they feed on living tissue  Direct transmission: parasite moves from one organism to another of the same species  Vector transmission: parasite requires an intermediate organism (a vector) to transfer hosts  E.g. Parasite plasmodium is transferred to humans by mosquitoes – they cause malaria 17 – dynamics of predation  Bottom-up control: resource availability and how it control population numbers  Top-down control: predation and how it influences prey population  In a study done to see the effects of predation and resources o hares, it was found that resource quality (vs availability) acted as the bottom-up control  When food is scarce, organisms switch to less desirable alternatives which usually have less nutrients and expose organisms to their predators - Happens at times of population peaks  Complex parasites require 2 hosts – prey as the intermediate (vector) and predator as the primary host  Parasites alter prey behaviour so they forage in places susceptible to predators - This increases the chances of transmission for the parasite’s benefit  Complex food webs experience more subtle shifts 18 – Keystone Species  E.g. Removal of the top predator starfish in the intertidal ecosystem resulted in the barnacle (that starfish preyed on) taking over  Removal of keystone species result in a drop in species diversity - Because keystones exert top-down control and prevents lower trophic species from taking over  Keystone mutualists such as hummingbirds, influence plants through pollination  Keystone modifiers such as beavers, alter the environment for other species as well as themselves  Keystone hosts like giant palm trees, provide habitat for other species  Keystone prey maintain their population number despite being preyed upon, thus controlling predator density  E.g. removal of wolves  elk population increase  overgrazing  plants population decrease  wildlife decreases  Keystone species play a disproportionately large role 19 – Species with a Large Impact on Community Structure  Dominant species are the most abundant species in a community  Both dominate species and keystone species influence their community via trophic interactions  Foundation species influence community by causing physical changes to the enviro
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