Entomology pg 180-195 EVOLUTIONARY ECOLOGY r and K selection do you produce lots of offspring and invest little? (r selection) Produce few offspring and invest lots r selection typical in: habitats which are hard to find habitats which exist for a short period of time typically over exploit their habitats locusts, aphids K selected Avoid overexploitation Regulated by density dependent factors (predation, etc) Some species show both at different stages of life Discussed survivorship curves (see lecture) Sexual Strategies Dispersal vs. fecundity Tradeoff ? energy spent dispersing is energy can?t be used reproduction Dispersal useful for patchy habitats Flightless Some insects lost ability to fly Females often can?t fly ? have to be larger to support reproduction, can?t get lift Energy, risk involved in flight Survival cost to mating ? male sperm may be toxic to females RESOURCE LIMITATION (p. 103-134) Density dependence Insect populations are regulates by density dependent factors r (increase/capita) is related to immigration/birth, emigration/death delayed density dependence: if density is high in one population, might not result in decrease in fecundity until following generation if long delay ? (delayed delay) ? oscillations Competition: when individuals require the same limited resource. Resource must be limited. Competition is a density dependent population factor Niche Fundamental: all the environments which could support the insect Realized: the environment the insect uses (as a result of competition, abiotic and biotic factors) Temperature dependent Some competition is temp dependent (high temps favor one species, low temps favor another ? environment varies, so neither species gains a 100% advantage) Drosphilia example Intraspecific competition ? within species Seems to be greater factor in density dependent population regulation than interspecific competition Evidence: the variety of species present in any given niche If interspecific was big, there?d be less species Interspecific competition ? between species Starting to interest researches again Does have some impact Insects with chewing mouth parts- comptetiion irrelevant Insects with sucking mouth parts ? competition relavent True of gall eaters as well Competition definitely impacts population Competition between guilds Insects of different feeding guilds (roots vs. above-ground for example) do compete if the plant is limiting Root herbivory: can kill plant, cause changes in foliage, loss of productivy, changes in tissue nitrogen concentrations In general: Damage to roots by below ground herbivores INCREASES performance of above-ground herbivores of the plant Root feeding increases foliar quality (especially in nitrogen content) Damage by above ground herbivores DECREASES perforamcne of below-ground herbivores Plant feeding decreases root biomass (growth) Leaf rolling insects sometimes improve quality of habitat for later chewers POSITIVE EFFECT However, if herbivory is great, declines in foliar quality may outweigh benefits of habitat improvement NEGATIVE Competition in fire ants ? intra and interspecific Intra: competition amoung queens when setting up colonies, brood and worker raids, etc. Result in evenly spaced colonies
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