2.05.15 (lecture) Notes PDF

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Prof. Joel Meyer...

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February 5, 2015 Lecture Notes Populations, Communities, and Ecosystems I. Interspecies (community) interactions and population growth  What’s wrong with the logistic modeling of population growth?  Presumes very tight “coupling” (feedback) between resource change and birth rates and death rates  Presumes that resource needs per individual are constant – that carrying capacity can be equated to some particular number of individuals o Is K a fixed number or a relationship?  Populations may be regulated by factors other than limiting resources including o Retarding factors (e.g. toxin and antibiotics) o Other organisms (competitors, predators, and parasites) COMPETITION & the ECOLOGICAL NICHE  G.F. Gause – competitive exclusion is when two organisms vying for the same resource cannot coexist indefinitely – one will eventually exclude the other  Species coexistence – occurs when multiple species coexist at a ratio of population sizes, or stable equilibrium  Fundamental ecological niche: the potential range of conditions and resources over which a species can maintain positive population growth (its range of tolerance for all the factors that it responds to) = in principle  Realized ecological niche: within its range of tolerance, the actual range over which an organism occurs taking into account the effects of other organisms = what really happens with the limitations  Variability in habitats allows variability of niches  biodiversity increases because species are allowed to specialize  Interference competition: prevent competitor from exploiting resources (direct)  Exploitation competition: more effectively use a limiting resource (indirect) SPECIES INTERACTION AND EVOLUTION  Type of interaction, effect on species 1, effect on species 2  Mutualism, +, + o Ex: Birds and capsaicin plants  Commensalism, +, 0 o Ex: Hermit crab uses the shell of a dead snail  Predation/parasitism/herbivory, +, – o Ex: Walnut tree kills other plants around it to use the resources  Neutralism, 0, 0  Amensalism, –, 0 o Ex: Poison ivy and humans  Competition, –, – Why would chili peppers produce capsaicin?  Capsaicin: molecule in hot peppers that gives you the burning sensation  Repels animals like deer and squirrels  Birds do not sense burning sensation of capsaicin and can spread the seeds in the process Invasive species and competition  Instances of competitive exclusion  Chestnut tree were wiped out by the chestnut blight in North America o 7 species of moth that only lived on these chestnut trees also went extinct  Kudzu was introduced to the US to prevent erosion and provide foliage for cattle o Wipes out other plants by preventing sunlight to pass through  Brown tree snake introduced to Guam and killed off 10 species of birds Parasites: Population Change

 2013: ~ 200,000,000 cases worldwide; ~500,000-1,000,000 deaths  Mosquitoes – Malaria as the “strongest known selective pressure in the recent history of the human genome” o We have evolved to defend against malaria  Sickle cell anemia and many other human diseases o Sickle cell anemia caused by two bad copies of gene o A recessive carrier of one bad copy will be resistant to malaria  Ex: sea lamprey and destruction of Great Lakes fish populations Predation and Top-Down Control on Population Size:  Mutually reinforcing oscillations with predator and prey populations  What if you remove the predator?  Effects on biomass and diversity can dramatic  Effects on biomass – can be a pyramidal structure of even a “inverted” pyramid  Effect on diversity of species  Paradox of predation and diversity: predators can increase the diversity of their prey by preventing any particular prey species from becoming too abundant and out-competing other prey species (via prey switching) FEEDBACK LOOPS AND HOMEOSTASIS  Feedback loop: a circular process whereby a system’s output serves as input to that same system  Dynamic equilibrium: when processes in a system move in opposite directions at equivalent rates so their effects balance out o Production of/loss of ozone; production of/loss of oxygen  Homeostasis: tendency of a system to maintain constant or stale internal conditions INTERSPECIES INTERACTIONS  Dynamic top-down, side-side, bottom-up contributions to the population size of any one species II. Case Study: Predator management NATIONAL PARK SERVICE: predator management  1890-1930: kill them  1930-1960: tame and “display” them  Today: restore them  Trophic cascade and example of “piece” management by the NPS o Ex: Gray wolf and quaking aspen o Correlation between wolves getting hunted and decreasing recruitment of young aspen o Reintroduced wolves  decrease in elk population  regeneration of aspen o Found that the aspen regenerated also because the presence of wolves changed the behavior of elk  Leopold: Father of wildlife management o Believed that you need predators for the development of an ecosystem o Made the mistake of wolf extirpation which resulted in deer and elk excess III. Characteristics and properties of communities KEYSTONE and FOUNDATION SPECIES  Keystone species’ importance in the ecosystem is disproportionate to biomass  Foundation species: dominant primary producer o Ex: quaking aspen  Effects of one change may involve many parts of community o Managing one species of two at a time may be ineffective (aka ripple effect should be regarded) o Which species or physical aspects of an ecosystem are most important?  Emergent properties: properties of a whole system not evident in the system’s components

o “The whole is more than the sum of its parts” o Philosophical question: is this a practical barrier or you really cannot understand the whoel by understanding the parts? o Reductionist (breaking a system into different parts) vs. systems approaches  Reductionist doesn’t help us understand the whole o Irreducibility vs. complex IV. From communities to ecosystems  Ecosystems = abiotic + biotic o Flow of energy and nutrients o Are ecosystems closed or open? – Boundaries can be artificially drawn for analytical convenience, but are ultimately false  Food web vs. food chain  Biogeochemical cycles: nitrogen cycle as an example o Nitrogen fixation (by bacteria in legumes or through fertilizers) to provide to plants o Nitrification o Denitrification o Ex: Fertilizer runoff in the Midwest into the Mississipi River  huge algae growth

 Relevance of community ecology o Wildlife management (on a bigger scale), protection of biodiversity  Rather than just protecting on species at a time o Addressing invasive species o Bioprospecting o Evolution of drug resistance, pesticide resistance, etc....