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Species • All individuals that are capable of interbreeding and produce fertile offspring A Population • Group of organisms of the same species living in the same place at the same time • Individuals may come and go, but the population can remain the same • Ex: The flamingos of Lake Victoria in Africa. – Assembled for yearly migration. • In a food web, each organism survives by gaining energy from the trophic level below it. • The size of the populations are continually adjusted by the species interactions with both its food supply and its predators. Carrying capacity: the largest population of a species that an environment can support. 4 factors that determine the carrying capacity: 1. materials and energy (energy, water, carbon, and other essential nutrients 2. food chains: the population size is limited by the size of the populations at lower trophic levels. (Prey limited by their predators and their food supply). 3. competition: each organism has the same need as any other. They compete for resources such as food, water, mates, space). 4. density: depending on their size, environment and way of life, different species have different needs for space. Closer look at competition: Two types of competition: 1. intraspecific: among members of the same species 2. interspecific: between different species A closer look at population density: • Two types of factors can also limit population sizes. 1. density-dependent factors: a factor that gets worse as the population size increases * overcrowding *parasites/disease *aggression amongst members * neglect of offspring • 2. density-independent factors: does not depend on the size of the population * forest fire * flood * volcano Population Growth • Not all populations grow the same way... Population Growth • Since all organisms reproduce, populations tend to grow over time • If unlimited resources are present, growth will be exponential • It will proceed very quickly for rapidly reproducing organisms and more slowly for slowly reproducing ones • The curve, however, will always be a “J” curve or an exponential growth curve Generation 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 # of bacteria 1 2 4 8 16 32 64 128 256 512 1024 2048 4096 8192 16,384 32,768 65,536 131,072 262,144 524,288 1,048,576 2,097,152 4,194,304 8,388,608 16,777,216 time 0 15min 30min 45min 1hr 75min 90min 105min 2hrs 3hrs 4hrs 5hrs 6hrs Population Growth 2 • Resources are never unlimited, though. • As population rises, resources decline. • If the growth is too rapid, resources are rapidly depleted and a population crash can occur • This pattern occurs often with many populations (including humans) • For example... Gypsy moth caterpillar Population Growth 3 • More often what happens is that the resources slowly decrease, the growth rate slowly decreases, and they meet. • This point that they oscillate around is the carrying capacity of the environment for that particular organism S - shaped curve Population Growth 3 Continued • Predator-Prey Relationship – Most food chains show this kind of growth, where as one organism increases in numbers, the other will decrease and vice versa. Human Growth Patterns What are the causes of the rapid growth of human populations? What are some possible consequences of this growth pattern? What will our future look like? (Remember the Reindeer?) Niche • The way an organism occupies a position in an ecosystem, including all the necessary biotic and abiotic factors • So for a brown bat, • Biotic: they eat insects, they compete with the common nighthawk, and are prey • Abiotic: where they roost or hibernate, when they hunt • Overall, they control insect population! Adaptations for Niche/Habitat • Pitcher plants can survive bogs, which have lots of water and sunlight, but it is an acidic place and is low in N • They consume insects (water will sit in plant and insect will drown and decompose, providing nutrients)