Learning Goal 1 Populations The Science of Ecology Definition – Levels of Organization in Nature – Features of Populations Population Characteristics – Population Dispersion – Survivorship Curves – Life History Patterns Consist Of – Fecundity vs Parental Care – Reproductive Episodes – Early vs Late Reproduction – R and K Selected Species – Models of Population Growth Growth Rate – Exponential Models – Logistic Models – Population Regulation Density Dependent Factors – Density Independent Factors – Human Population Growth Increased Carrying Capacity – Population Growth and Age Structure – Demographic Transition Model -

Ecology Learning Goal One Analyze aspects of populations in terms of life history patterns, growth models, limiting factors, and human population trends.

What’s Wrong with This Picture?

The Science of Ecology Definition Ecology is the study of interactions between organisms and their environment. The environment consists of both abiotic and biotic factors. Abiotic components consist of nonbiological factors such as temperature, water, soil chemistry. Biotic componenents consist of biological factors such as plants, microorganisms, and animals.

Levels of Organization in Nature Organisms Individuals within a population. Populations Made up of individuals of the same species. Community Made up of all populations in an area. Ecosystems Includes the community as well as the physical environment. Biosphere Refers collectively to all ecosystems on earth.

Features of Populations Population Characteristics Population size refers to the total number of individuals in any given population. Density refers to the number of individuals per unit area of habitat.

Population Dispersion Clumped Individuals are grouped together. Uniform Organisms are evenly spaced in their habitat because they repel each other. Random Organisms are distributed unpredictably. Used when the other two dispersion patterns don’t apply.

Survivorship Curves Type I High survivorship until late in life. Depict changes in survival rate. Type I High survivorship until late in life. Type II Relatively constant rate of mortality at all ages. Type III High juvenile mortality followed by low mortality once a certain age or size is reached.

Life History Patterns Consist of: Growth Increase in cell number from birth to maximum size for that species. Maturation Usually refers to the point where sexual maturity is reached. Reproduction Offspring is produced to ensure the survival of the species.

Fecundity vs Parental Care Passive Parental Care Energy is invested in offspring before birth. ie., egg yolks, endosperm in seeds, nutrients that cross placenta Active Parental Care Continued parental care after birth. Fecundity refers to the number of offspring produced during a female’s lifetime. Organisms that produce large numbers of offspring are generally passive parents whereas low numbers of offspring receive active care.

Reproductive Episodes One Episode All energy is devoted to one reproductive event, like the salmon and most insects. Several Episodes Other species devote only some of their energy budget to reproduction so spread it out over many episodes with the rest allocated to maintenance and growth.

Early vs Late Reproduction Early Reproduction Favored by natural selection if adult survival rates are low as in a prey species, or adults do not increase in size as they age (they’re small). Late Reproduction Favored by natural selection if sexually mature individuals have a good chance of surviving to produce more offspring.

R and K Selected Species R-Selected Species Function well in rapidly changing environments. Usually small and produce numerous offspring often in a single reproductive event. Little or no active parental care. Most die before reaching sexual maturity so success depends on producing so many that a few are likely to survive.

K-selected Species Thrive in more stable environments. Larger with longer generation times. Produce offspring repeatedly throughout their life time. Offspring receive substantial parental care. Small number of offspring.

Models of Population Growth Growth Rate - Change in population size = number of births (B) – number of deaths (D) Normally expressed in births (b) and deaths (d) per capita (individual) during a specified time period. B/N = b and D/N = d (N = population size) Growth rate r= b-d

Occurs when populations are exhibiting unlimited growth. Exponential Models Occurs when populations are exhibiting unlimited growth. Assumes unlimited resources and no build up of toxic waste products. Population size increases by a constant ratio. Graphs of exponential growth are known a J curves because of their characteristic shape.

Logistic Model Most populations exhibit a logistic model of growth. Growth increases rapidly at first then slows down as the population gets larger. As resources run out fewer offspring are produced and a population reaches its carrying capacity, the maximum number of individuals that an environment can support. Logistic models exhibit an S-shaped curve.

Population Regulation Density Dependent Factors Factors that have more impact as population density increases.

Intraspecific Competition Competition between members of the same species. Leads to decrease in reproduction, slower growth, and smaller adult size. May stimulate behavioral and developmental changes as with locusts. Some will become migratory with longer wings and more body fat so they can fly great distances.

Other Examples of Density-Dependent Factors Interspecific Competition Competition between different populations. Disease Microorganisms spread quickly in denser populations.

Density-Independent Factors Factors that reduce population size regardless of its density. Climate, fires, earthquakes, storms are some examples. Density-Independent factors do not cause a population to fluctuate around its carrying capacity the way density dependent factors do. They reduce, but do not regulate populations.

Cycles in Population Size Intrinsic Control: As population grows, individuals undergo hormonal changes that may cause aggressive behavior, or reduced reproduction, or lead to migrating to other areas. Extrinsic Control: Population cycles in response to food and/or predators.

Human Population Growth Ways Humans Increased carrying capacity: 11,000 years ago humans shifted from hunter/gather cultures to agriculture. They cultivated plants and domesticated animals and significantly alter their environment by diverting water for irrigation and building settlements. Once the energy from fossil fuels was harnessed in the mid eighteenth century food supply increased further.

Advances in Public Health: Reduced malnutrition, contagious diseases, and improved sanitation all reduced death rates sharply.

Population Growth and Age Structure Zero Growth: Equal number of people in prereproductive and reproductive age groups. Slow Growth: Slightly more prereproductive than reproductive population Rapid Growth: Broad base of prereproductive population. One third of the world’s population.

Negative Growth: Fewer prereproductive individuals that any other age group.

Demographic Transition Model Preindustrial Stage-Birth and death rates are high and population grows slowly. Transitional Stage-Food production rises, health and sanitation improve leading to decreasing deaths. Industrial Stage –Birth rate declines as more people move to cities. Postindustrial Stage – Birth rate equals or falls below death rate leading to ZPG or declining population growth.

Options for Limiting Population Growth Family planning programs that limit human population growth. Wait until the environment does it for us.

LG 1 Terms Abiotic/Biotic Components Levels of Organization in Nature Population Size vs Density R – Selected Species K – Selected Species Exponential vs Logistic Growth Model Carrying Capacity Density Dependent Factors Density Independent Factors Demographic Transition Model