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BIOA02 Module 3 Lecture 4

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Biological Sciences
Monica Sauer

Lecture 4 - Population Ecology III In real life, it’s not usually tidy (Logistic and Exponential): Time lags in population response to increased density Carrying capacity is an example of population regulation (a way which allows species to coexist) Many factors regulate populations: change the size and growth rate of populations. Some factors are density dependent factors: the importance of the factor in changing the population depends on the size (density) of the population. Usually: ↑ density = ↑ overall impact • Resource consumption (provided w/ x amount of resources) • Predation • Health: Starvation, Disease Spread, Parasites! • Territoriality / Mating • Waste accumulation • Intrinsic (behavioural) factors (ie killing each other off for space) Some factors in the environment are (extrinsic) density- independent: they are external to the population and the impact does not depend on the size of the population (these are abiotic processes) • Availability of many resources • Climate variation Lecture 4 - Population Ecology III • Natural disaster Population Regulation in Daphnia spp: --> Density-dependent regulation of population fecundity Escaping regulation – how some species boom (suspectible to decline in resources leading to a "bust") • Invasive species are organisms that are able to spread uncontrollably. In other words, they do not experience adequate population regulation. • Invasive species are usually introduced from their native range to a new area (on purpose, have large impacts). In its new habitat, we call the species non-native, exotic, or alien. BUT non-native species are not always invasive. • When they are introduced, non-native species sometimes escape their predators, pathogens, and parasites. These forms of regulation are not transferred or cannot survive in the new habitat. • Non-native species may also adapt to acquire more resources or utilize new habitats. Invasive species often share some common traits (outcompete native species) • Few predators (or herbivores, for plants). These may be ‘left behind’ in the native range. • Adaptable. Population bottlenecks and strong selection pressures in the new range select robust, adaptable phenotypes. • Reproduce quickly. A key trait of invasive species: they have higher fecundity than their native neighbours. • Thrive in disturbed ecosystems. Invasive species are often human adapted, meaning they thrive under conditions of human disturbance. They also tend to acquire resources Lecture 4 - Population Ecology III quickly and use them quickly, which takes advantage of the resources released by disturbance. • Out-compete native species for resources. All the above traits combine to make highly competitive species who suffer fewer population regulations and acquire a larger share of resources than their neighbours. Population Regulation can have Large-Scale Consequences! • The Mountain Pine Beetle (Dendroctonus ponderosae) is a bark beetle native throughout NA. • The MPB normally helps
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