Transcript Chapter 19
Ecology • The study of how organisms interact with each other and their environment Key Elements of the Environment • Temperature – most organisms require a narrow range (humans excluded) • Water – very important, much more diversity in rainforest than in desert • Sunlight – where almost all energy originates from • Soil – pH, minerals, nitrogen, phosphorus affect the ability of plants to grow Population properties • Population size – number of individuals • Population density – number of individuals in a given unit – – – – Los Angeles – 7544 people/square mile South Sioux City, NE – 2725 people/square mile Manila, Philippines – 111,576 people/square mile New York City – 27,012 people/square mile • Population dispersion clumped uniform random Population growth • Population at current time = population from past time + births during that time – deaths during that time + immigration – emigration – Simulation of population growth – start off with 10 people (5 couples) – each couple has 4 kids • • • • How many offspring? - 20 20 children become adults and each couple has 4 kids How many offspring? – 40 Doubles each generation – so let’s draw a graph Population growth • Exponential growth – the larger the population, the more it will grow • Eventually this has to stop – Space – Availability of resources • Carrying capacity – the max population • This type of growth is called logistic growth (sometimes called a sigmoid curve) Factors that influence population density • Density-independent events – Severe weather (floods, drought, etc.) – Severe geological disturbances (volcanoes, earthquakes, etc.) • Density-dependent events – Aggressive behaviors (defending territory) – Emigration Maximizing population productivity • Demand for fish has increased due to general health benefits and increase in global population • Overharvesting has caused population decline in wild salmon • Salmon farms have helped alleviate the problems of overharvesting • Farms have negative health and ecological impact – Toxins in fish – Fish lice and viruses are becoming common if farmed salmon, which are passing them on to wild salmon overharvesting Wasting resources Maximum sustainable yield Demography • The study of populations using statistics • Cohort – A group of individuals that are the same age • Fecundity – Number of offspring produced in a standard time (for example, a year) • Mortality – The number of individuals that die in that time • Proportion of males to females is called the sex ratio Survivorship curve • Type I – Most live a long time, then suddenly die • Type II – constantly die off • Type III – many die off young, the ones that survive live for quite some time Community and Ecosystem • Community - all the species in a given area • Ecosystem – all the species and all the nonliving components in a given area The Niche and Competition • Niche – all the ways in which an organism uses its habitat • Habitat – the place where an organism lives • Competition – when two organisms attempt to use the same resource – Interspecific – between two different species – Intraspecific – between the same species Fundamental Niche vs. Realized Niche Fundamental Niche – where a given species is ABLE to live Realized Niche – where a given species actually lives because of competition Competition Population • Competitive exclusion - If two species are competing for the same resource, the one that uses it more efficiently will out grow the other Time P. Bursaria grown separately • No two species can occupy the same niche if resources are limited. If two species coexist… • Resources are not limited • They do not occupy the same niche Resource partitioning • Competition between two species is rare in nature because of 2 reasons: – One would outcompete OR – A new niche would be formed by dividing up resources – resource partitioning • Sympatric – closely related species that divide up resources – must live close to each other • Allopatric – closely related species that do not divide up resources – so usually do not live close to one another • Allopatric species look more alike than sympatric species – called character displacement Character Displacement • Character displacement is not the same as disruptive selection Coevolution • Symbiosis – two organisms that live together and whose existence is altered because of this relationship – Mutualism – both benefit – Commensalism – one benefits, other is unharmed – Parasitism – one benefits, other is harmed • Sometimes parasitism can be considered a predatorprey relationship Predator/Prey cycles • Predation – the consuming of one organism by another – Predator – the one doing the eating – Prey – the one being eaten Defense against predators • Plants – – – – – Thorns Spikes Prickles Chemicals (pungent tastes usually associated with toxicity) Many others • Animals – – – – – Poisons Warning coloration Camouflage Speed Many others Mimicry – a type of defense • Batesian mimicry – non-harmful organism mimics the look of a harmful organism • Mullerian mimicry – similar pattern development between harmful organisms • Self-mimicry – one body part looks like another body part Mullerian Batesian poisonous Non-poisonous venomous Mullerian Ecological succession • Succession – more complex communities replace simpler ones as time goes on – Primary Succession – occurs on a substrate that never had life prior • Examples: volcanoes, rocks, lakes left by glaciers – Secondary Succession – occurs on a substrate that had life prior, but was almost completely wiped out • Deforestation, flood, fire