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III. POPULATION. Doris V and Ne’Shonda D. POPULATION BIOLOGY. Population Biology. Exponential Growth: has no limits and has a J curve when graphed (population size can be small at first but quickly increase in a short time)
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III. POPULATION Doris V and Ne’Shonda D.
Population Biology • Exponential Growth: has no limits and has a J curve when graphed (population size can be small at first but quickly increase in a short time) • Carrying Capacity: the maximum number of individuals that can be supported by an ecosystem • Overshoot: population exceeds carrying capacity, resources become limited, & death rates rise • Population Crash: deaths exceed births (dieback) • Boom & Bust Cycles: repeatedly overshooting carrying capacity & then crashing catastrophically
Population Biology • Logistic Growth: Growth rates regulated by internal (maturity, body size, & hormonal status) external factors (habitat quality, food availability, & interactions with other organisms) that establish a balance with environmental resources • Logistic growth has a sigmoid growth curve (S curve), in which the population begins decreases if it approaches its carrying capacity
J & S Population Curves Biotic potential: maximum reproductive rate of an organism given unlimited resources & ideal environmental conditions
R-selected vs. K-selected species R-selected species K-selected species Reproduce slowly Few offspring Growth slows as they reach their carrying capacity Higher trophic levels Long life Late maturity High parental care Niche specialists Predators • Rapid reproduction • Many offspring • Frequently overshoot their carrying capacity & display boom & bust cycles • Low trophic level • Short life • Early maturity • Little parental care • Niche generalists • Prey
Density-dependent and Density-independent factors that regulate population growth • Density-dependent; results from interactions between populations of a community (extrinsic or interspecific) or interactions within a population (intrinsic or intraspecific). • Lotka-Volterra model: when prey populations are abundant, predators reproduce more successfully and their population grows. When the prey population crashes so does the predator’s. • e.g. stress (stress-related diseases) from overcrowding, territoriality, • Density-independent; factors that affect natality or morality independently of population density tend to be abiotic components of the ecosystem • Weather and climate are the most important factors. Drought, excessive rain, severe storms, volcanic eruptions, landslides, and fire.
Logarithm of Survival Population Biology: Survivorship Dependency Period Reproductive Period Postreproductive Period
Conservation • For many species, loss of genetic diversity causes a number of effects that limit adaptability, reproduction, and survival. • Demographic Bottleneck; just a few members of a species survive a natural disaster or colonize new habitat isolated from other members of the population. Any deleterious genes in survivors will magnify in future generations • Minimum viable population size; the number of individuals needed for a long-term survival of rare and endangered species
Conservation A metapopulation is a collection of populations that have regular or intermittent gene flow between geographically separate units A “source” habitat; where birth rates exceed death rates, individuals migrate to new location a “Sink” habitat is the opposite.
Case Study: How many fish in the sea? • Cod was so abundant many thought the animal could never be threatened by humans • Fishing technology grew larger and more efficient • Seafood accounts for 140 million metric tons of food annually • Researches predicted that the world’s major seafood population will collapse by 2048 • Several countries have placed bans and restrictions on fisheries
Human Population Dynamics: Historical Population Sizes In the Middle Ages, populations were held in check by disease, famine, and wars. After 1600 human population began rapidly increasing because of commerce and communication between nations, agricultural developments, better hygiene, and better healthcare.
Spatial Distribution • Random: Most uncommon, can only occur if the environment rarely changes • e.g. some spider species • Uniform: most predators due to territoriality & space needed for hunting • Clumped: Most common because resources are concentrated in specific areas and also for protection
Fertility Rates • Total Fertility Rate: the number of children born to an average woman in a population during her entire reproductive life • World’s fertility rate: 2.7 • Mexico’s fertility rate 1975: 7 2006: 2.4 • China’s fertility rate 1970: 6 2006: 1.6 • According to WHO all but a few developing countries are expected to be at or below a replacement rate of 2.1 by 2050.
Growth Rates • Rule of 70: 70÷ growth rate= Doubling time • Natural Increase: Crude birth rate-crude death rate • Crude birth rate: Crude birth rate: number of births in a year per thousand persons • Crude death rate: number of deaths in a year per thousand persons • Zero population growth: (births+immigration)=(deaths + emigration) Niger growing at 3.4% per year will double in 20 years. The US growing at .6% per year will double in 116.7 years. The Ukraine with a growth rate of -.8% will lose 40% of its population in the next 50 years.
Demographic Transition • Demographic transition: pattern of falling birth and death rates in response to improved living conditions • 4 factors that must be present: • Children must reach maturity • Higher standard of living • Improved social status for women • Birth control must be accessible • Birth Dearth: birth rates fall to below replacement rates; common in Europe
Age Structure Diagrams -First Stage: High birth rates and high death rates, especially in older cohorts. There is not much education, medications, or sanitation. -Second Stage: High birth rates, but a decrease in death rates. Life expectancy is a bit longer due to some improvement in living standards. -Third Stage: Low death rate and declining birth rate. Longer life expectancy due to a more industrialized way of life. Approaching final stage. -Fourth Stage: Stable population without much change. Low death and birth rates.
Stabilizing Population Optimistic • Growing prosperity & social reforms that accompany development reduce the need and desire for large families in most countries • Technology brings advances • Less developed countries have historic patterns to follow Pessimistic • Others advocate strongly for birth control education and national policies to encourage lower birth rates.
Family Planning • Family planning allows couples to determine the number and spacing of their children. • Birth control: any method used to reduce births, including abstinence, delayed marriage, contraception, methods that prevent the implantation of embryos, & induced abortions
Family Planning • Pronatalist Pressures: factors that increase people’s desires to have babies • Children can be a source of pride and happiness • Future source of support or even current income • Society must replace members who die • Factors that discourage reproduction: • Higher education & freedom for women • Expensive to raise children
Case Study: Family Planning in Thailand • The PDA (Population & Community Development Association)founded by Mechai Viravaidya in 1974. • The campaign not only encouraged condom use, but also helped in combating AIDS. • 1974 growth rate: 3.2% Contraceptive use: 15% • 1999: growth rate: 1.6% contraceptive use: 70% • Now the growth rate is .7% and the fertility rate dropped from 7 in 1974 to 1.7 in 2006. Without the PDA Thailand would have 20 million more people added to their population.
Social Justice • Social justice: a fair share of social benefits for everyone • The world has enough resources, but they are not equitably distributed. • Hunger, poverty, overpopulation, and environmental degradation are symptoms of a lack of social justice, not resources. • Women play a huge role in fertility rates. They must have rights to own property, work, access to education, and have political rights to lower fertility rates. If they have educational opportunities they are more likely to postpone marriage & childbirth.
Impacts of Population Growth: Hunger • Despite past predictions of famine, food supplies have increased to keep up with population growth due to advances in technology, even developing countries saw a rise in supplies • Although famines have stricken several areas, they were caused more by politics and economics than by lack of resources or population size. • But even in a world of surplus food, over 850 million people don’t have enough to eat • Poverty is the greatest threat to food security, ability to obtain sufficient food on a daily basis
Disease • With progressing technology, many diseases like Polio, Smallpox, Typhoid fever, Cholera, AIDS, etc. that killed thousands have recently been wiped out completely or are now highly treatable. • Infectious and emergent diseases still take millions of lives • Resistance to drugs and antibiotics is increasing because of misuse and genetic resistance spreading throughout populations
Resource Use and Habitat Destruction • Every year thousands of acres of natural habitats are being destroyed to make room for human expansion. • With an increasing population more room and resources are needed to keep up with demand. • Resources are being used at a faster rate than they can be naturally replenished. • A need has risen develop new ways to be more sustainable to prevent further destruction of habitat and resources while still meeting current need
Strategies for Sustainability • Smart Growth: the planned development of cities that make use of infrastructure & makes more efficient use of land resources, while protecting environmental quality • Attempts to reduce traffic and conserve wetlands, farmlands, and open space. • Some states have instituted development rights, where owners of rural land are paid to prevent development on the outskirt of cities • This restricts urban growth and protects farmland for future generations.
Strategies for Sustainability • Green Cities: cities are redeveloped in a more environmentally sound fashion • They have more green space and use mass transit, ride-sharing programs, or bicycling routes. • They can employ reclaimed water systems, have comprehensive recycling programs, have green roofs by growing plants on their rooftops to help filter pollutants, absorb water, and cool the area. • Can reclaim brownfields& abandoned industrial sites.
