Grade 12 Biology: Population Dynamics

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Population

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A group of individuals of the same species living in the same geographical area

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Population Size

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The number of individuals of the same species occupying a given area/volume at a given time

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Population Density

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The number of individuals of the same species that occur per unit area or volume

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Crude Density

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Population density within the total area of habitat

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Ecological Density

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Population density within useable area

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Population Distribution Types

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Clumped, uniform, random

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Clumped Distribution

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- most common

- social organisms

- in a pack, herd, school of fish, bat colonies, cattails, etc

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Uniform Distribution

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- rate in nature/wild

- in crops

- nesting penguins, orchard/tree plantation

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Random Distribution

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- maple trees in a forest, orangoutangs in rainforest

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Calculating Population Density

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D = N/S

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Methods of measuring population characteristics

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- Indirect indicators (tracks and droppings, etc...)

- Quadrat sampling

- Mark-recapture method

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Carrying Capacity

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The maximum number of organisms that can be sustained by the available resources over a period of time

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Levels of species at risk

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Extinct, extirpated, endangered, threatened, special concern

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Extincr

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Any species that no longer exists on Earth (Great Auk, Labrador duck, Long-nosed dace...)

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Extripated

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Any species that no longer exists in Canada (Black-footed ferret, Timber rattlesnake, Frosted elfin...)

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Endangered

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Any species close to extinction in all or part of Canada (Eskimo curlew, Northern cricket frog, Spotted turtle...)

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Special Concern

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Any species at risk due to low or declining numbers (Grizzly bear, Peregrine falcon...)

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Factors influencing the risk status of a species

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Size, range, biotic potential, diet, human interactions

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Mark-recapture method formula

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M (total marked)/N (total population) = m (number of recaptured marked)/n (size of second sample)

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Factors that affect population growth

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Death, birth, immigration, emigration

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Population change formula

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Population change = [(b+i) - (d+e)]/n

Multiple answer by 100%

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Open population

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Birth, immigration, death, and emigration affect population

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Closed population

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Only birth and death affect population (no immigration or emigration- islands, zones...)

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Exponentiel growth

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Population is continually growing- no breeding season (eg. humans, yeast)

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Geometric growth

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Population increases during breeding season and decreases at other times (eg. population with 1 breeding cycle per year)

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Logistic growth

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Growth that levels off as the population nears its carrying capacity

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Phases of logistic growth

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- lag phase

- log phase

- (exceeding phase)

- stationary phase

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Causes of species decline

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Habitat degradation/loss, water, soil, and air pollution, overexploitation, alien species, and disease

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Factors of life histories of populations

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Age when it sexually matures, how often it reproduces, number of offspring that survive to reproduce, and fecundity

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Fecundity

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The average number of offspring produced by a female member over her lifetime

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Survivorship curves – type I

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Species with a high survival rate of their young, most of the individuals are expected to die only when old- high parental care (humans, large mammals- bear)

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Survivorship curves- type II

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Species in which individuals die at a constant rate from hunting, disease, etc. (Chipmunks, bees, many reptiles, and birds)

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Survivorship curves- type III

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Species in which most individuals die when young, many babies are born, but few survive long- low parental care (plants, most fish, sea turtles, many insects)

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Examples of animals in different survivorship curve types

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Type I: humans, orca

Type II: coral, loan

Type III: plants, mice

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Density independent factors

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Limiting factors

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“r” species

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Species whose population is well below the carrying capacity and can still grow exponentially with the rate (r)

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“K” species

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Populations that are at their carrying capacity

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r strategy

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Unstable environment, small size of organism, low-energy used to make each individual, many offspring produced, early maturity, short life expectancy, reproduces only once, type III survivorship pattern

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K strategy

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Stable environment, large size of organism, high energy used to make each individual, few offspring produced, late maturity due to prolonged parental care, long life expectancy, can produce more than once, type I and II survivorship pattern

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Density dependent factors

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Intraspecific competition, predation, Allee effect, minimum viable population size

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Intraspecific competition

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Individuals compete for nest space, food, light, etc., with others of the same species [high density trees – lots of shade, little water,few nutrients per tree]

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Predation

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Predator view point: more prey/predator equals more food, less prey/predator equals more intraspecific competition

Prey view point: more prey/predator equals less chance of being eaten, less prey/predator equals more chance of being eaten

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Allee Effect

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Reproduction fails to equal mortality due to low density

eg. cannot find a mate, species that rely on overwhelming predators can’t do so when numbers are low- passenger pigeons

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Minimum viable population size

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The smallest number of individuals that ensures the population can persist for a determined amount of time [with human help 23 whooping cranes was enough, in wild, 100 elephant seals was enough; for many species 200+ are needed for this]

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Limiting factor

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Any essential resource that is in short supply or unavailable that can cause a population decrease [tend to be abiotic – temperature, pH, chemicals, non-contagious disease]

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Camouflage

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Leaf-like praying mantis, seals, often insects

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Toxins

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Blue ringed octopus, scorpion, monarch butterfly, usually bright in colour to warn predators

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Mimicry

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Batesian mimicry: harmless mimics harmful

Mullerian mimicry: harmful mimics harmful

Mimicry examples: monarch butterfly, eastern coral snake

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Types of symbiosis

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Mutualism, commensalism, parasitism

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Mutualism

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Both species benefit [ e.g. oxpecker and giraffe, moth and cactus flower]

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Commensalism

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One benefits and other is unaffected [e.g. algae on a turtle’s back]

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Symbiosis

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Relationship between individuals of two species

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Parasitism

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One species benefits and the other is harmed [e.g. mosquito and human]

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Stability in a community

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Population doesn’t exceed carrying capacity – population is in equilibrium

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Instability in a community

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A natural disaster occurs, population exceeds carrying capacity, or an exotic species introduced; populations equilibrium is disrupted

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Types of interactions within communities

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Interspecific competition, predation, defence mechanisms, symbiosis, disruptions of communities

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Exotic species cases

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Zebra mussels brought from Asia to Canada by accident in freshwater streams, starlings from the UK, cane toad from Hawaii to Australia introduced as a method of pest control that didn’t work so the population exploded

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Early humans

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– Homo sapiens sapiens is arose in Africa about 200,000 years BP

- Small populations moved out of Africa as hunters/gatherer’s

– birth rates were low, death rates were high [especially among very young, old, and L] due to nomadic lifestyle

– slow population growth, clumped just version [coastal areas especially]

– 12,000 years ago, population equalled about 5 million

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The agricultural revolution

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– 11,000 years ago humans began to domesticate plants and animals [agricultural revolution]

– human populations were stationery, birth rates increased, population densities increase

– death rates remain high – disease

– epidemics occurred in densely populated areas and where humans were in contact with animals, even so population growth increase

– about 2000 years ago the world population was 300 million with the doubling time of 2000 years

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The industrial and scientific revolution

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– Population growth increase dramatically – exponential

– power driven towards lead to mass production of goods

– advances and Chemistry like to production of fertilizers and pesticides [increased food production]

– advances in medicine like to clean drinking water, sewage system, and development of vaccine

– death rates dropped especially among young

– population explosion began – doubling every 50 years

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Most populated countries

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China, India, USA, Brazil, Indonesia

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Factors impacting world’s population

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Fertility, life expectancy, HIV/AIDS, ageing population, migration

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Current world population versus 2050

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2018: 7.4 billion

2050: 8.9 billion

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Four stages of human demographic transition

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Pre-industrial, transitional, industrial, post-industrial

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Pre-industrial

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High birth and death rate, population is fairly stable, as little surplus of food, there is agriculture but yield is low

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Transitional

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Agriculture surpluses cause people to move to cities [farms can see distant populations], population start to increase the girl dramatically, birth rate decline slightly (people choose to have less children), death rates drop due to hygiene and healthcare

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Interspecific competition

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Two or more species compete for the same resources – restricts population growth [e.g. competition for nesting space, pret, etc.]

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Industrial

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Population continues to grow, birth rate continues to drop as more people to small families, death rate drops faster do the food and health care advances

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Post-industrial

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Population actually starts to decrease, death read a study, birth rate falls even more a smaller families become the rule

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Pre-industrial countries

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Namibia , Ethiopia

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Transitional countries

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Kenya, Mexico

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Industrial countries

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Brazil, India

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Post-industrial countries

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Canada, many countries in Europe

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Growing population characteristics

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Many young people [ 0–15] who will later become reproductive [15–45] and few people [45+]; little infrastructure for elderly

Example: Nigeria

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Growing population environmental consequences

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Currently has a low impact on the environment [With exceptions], societies are in transition and use limited amount of natural resources; however, these societies are growing rapidly so in the future there will be a larger impact

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Stable population characteristics

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Equal numbers between 0-15 and 15–45; current reproductive group replaced by a similar sized group, but much larger than in growing population

Example: Spain

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Stable population environmental consequences

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Currently has a moderate impact on the environment, societies are industrial and use lots of natural resources, the society is going slowly and becoming more advanced so in the future there will be a larger impact

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How is interspecific competition reduced?

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Competition is reduced by resource partitioning which means species occupy slightly different niches

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Negative growth population characteristics

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You were young people then people between 15–45; a reduction in reproductive numbers is coming as well as an increase in elderly

Example: Germany

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Negative growth population environmental consequences

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Currently has a very high impact on the environment, societies are post-industrial and use vast resources amount of resources; however, this society is slowly shrinking and so in the future there will be a reduced in fact

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What factors determine whether the worlds population continues to grow, stabilizers, or crashes?

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Poverty, disease, war, population control measures, environmental impacts

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What are the most important issues facing human populations today?

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Consumption and waste, climate change, disease, deforestation and soil erosion, urban expansion, poor to wealthy gap, desertification, freshwater pollution, loss of biodiversity, emerging diseases, terrorism, international conflict

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Niche

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And ecological niche is an organisms biological characteristics, including use of and interaction with abiotic and biotic resources in the environment

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Fundamental niche

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Niche in ideal conditions

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Realized niche

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Actual niche due to competition

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Predation

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Morphological

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Types of defence mechanisms

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Morphological, camouflage, toxins, mimicry

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Morphological

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Physical protective features [E.g. turtles shell, cacti spine, horns, spikes, often plants, etc.]