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Transcript
Populations C-5-1 Exponential Growth • Populations can grow exponentially if not kept in check. • ~ for instance: one bacteria will become 2, then 4 then 8,then 64, then 512,then at the end of one day, there will be 4.72 x1021 Exponential Growth • only happens when populations have every offspring survive to reproduce. • As resources become less available, offspring don't live as well. This stops population growth. • Carrying capacity – max # org. an ecosystem can support Exponential Growth • Human population has grown exponentially since the 1700's. – due to medicine and farming technology: • people live longer lives • vaccines lower death rates • more food supports more people • We have not reached carrying capacity yet, but some evidence shows we may reach 9 bill. by 2060 • Ecosystems are influenced by a combination of biotic (living organisms) and abiotic (physical) factors. Limiting Factors for populations • Density-dependent – Competition for food - more org. = less resources – Predation - predator-prey relationships keep each other in balance – Parasitism and Disease - keeps populations down by killing host Limiting Factors for populations • Density-indepenant – Drought / Climate extremes – extreme heat or cold, lack of or too much water...all can kill – Human disturbances - changing the ecosystem ~ deforestation, waste dumping, killing off predators • DDF - only become limiting when the pop. density reaches a certain level • DIF - affect all pops. similarly regardless of pop. size • Through a combination of all of these factors, populations can vary from being in balance, to being way out of balance. Interaction in Communities C-5-2 • There are many different ways species can interact with each other within their communities... Interactions • Competition – species have similar needs and compete for survival • Predation – one org. eats another – back and forth adjustment between the 2 results in coevolution – ex: the faster the prey gets, the faster the predator gets and vice versa Interactions • Symbiosis - relationship where 2 species live closely together. 3 types: a.) Mutualism - both species benefit ex: flowers and insects b.) Commensalism - one benefits, the other is neither helped or harmed ex: barnacles on a whale c.) Parasitism - one org. lives on another and the host is harmed ex: tapeworms in mammals Shaping Communities C-5-3 • Habitat – area in which an org. lives • Niche - all conditions in which an org. lives and how it uses those conditions – – – – type of food eaten place in the food web temp. in which they survive reproduction style – Fundamental niche - where a species could live – Realized niche - where a species actually lives • No two species will share the same niche in the same habitat! • Competitive exclusion principle – no 2 species can occupy the same niche in the same habitat at the same time – this would result in the elimination of one of the species • keystone species – these are critical to the ecosystem because they affect the survival and number of many other species in their community – Ex. Sea otters • Ex: sea otters: – sea urchins eat kelp - sea otters eat sea urchins – when sea otters are over hunted, too much kelp gets eaten by urchins - all other species that use the kelp to live in lose their home. – sea otters are critical to the survival of the ecosystem Summary • The more species in a community, the better • It will recover from disasters. • The predators help insure that no one species takes over. • More biodiversity = better resiliency