Environmental Science - Population Dynamics PDF

GEE 200 ENVIRONMENTAL SCIENCE MIDTERM LESSON 3 POPULATION DYNAMICS Population size changes due to four main factors: birth, mortality, immigration,...

GEE 200 ENVIRONMENTAL SCIENCE MIDTERM LESSON 3 POPULATION DYNAMICS Population size changes due to four main factors: birth, mortality, immigration, and emigration. Here’s a breakdown of each: 1. Birth (Fertility): This refers to the number of live births in a population over a specific period. Higher birth rates contribute to population growth, while lower birth rates can slow it down. Factors influencing birth rates include cultural norms, economic conditions, access to family planning, and maternal health. 2. Mortality (Death): Mortality rates reflect the number of deaths in a population during a given timeframe. A high mortality rate can lead to population decline, while a low mortality rate typically contributes to growth. Key factors include healthcare access, disease prevalence, and lifestyle choices. Improvements in healthcare can lead to decreased mortality and increased life expectancy. 3. Immigration: This is the influx of people into a population from other areas or countries. Immigration can increase population size and bring diversity, skills, and economic contributions. Policies, economic opportunities, and social factors often drive immigration trends. 4. Emigration: Conversely, emigration refers to the outflow of people leaving a population. High emigration rates can reduce population size and may result from factors like economic instability, conflict, or the search for better living conditions. Together, these factors interact to shape the dynamics of population growth or decline in any given area. Population size is influenced by both density-dependent and density-independent factors, each playing distinct roles in regulating populations. Density-Dependent Factors These factors are influenced by the population size itself. As the population increases, the effects of these factors become more pronounced. Common examples include: 1. Competition: As population density increases, individuals compete for limited resources like food, water, and space. This can lead to decreased growth rates or higher mortality. 2. Predation: Higher population densities can attract more predators, increasing predation rates on prey species. 3. Disease: Crowded conditions can facilitate the spread of diseases, leading to higher mortality rates as the population grows. 4. Waste Accumulation: Increased waste from a larger population can lead to pollution or toxic conditions, negatively affecting health and survival. Density-Independent Factors These factors affect population size regardless of density. They can cause sudden changes in population size and include: 1. Weather Events: Natural disasters like hurricanes, droughts, or floods can drastically reduce populations regardless of their size. 2. Climate Change: Long-term changes in climate can alter habitats and resource availability, impacting species without regard to their population density. 3. Human Activities: Actions such as habitat destruction, pollution, or the introduction of invasive species can significantly impact populations irrespective of their size. 4. Accidents: Events such as fires or industrial accidents can lead to sudden population declines. Summary In essence, density-dependent factors regulate populations more closely linked to their size, often leading to feedback loops that stabilize population dynamics. In contrast, density-independent factors can cause abrupt changes that are not influenced by population density, often leading to dramatic shifts in population sizes. Population growth can be characterized by different growth curves, each representing distinct patterns of population change over time. The two primary types of growth are exponential growth and logistic growth, along with some variations and specific models. Here’s an overview: 1. Exponential Growth (J-Curve)  Description: In exponential growth, a population increases rapidly in an ideal environment with abundant resources. The growth rate is constant and independent of population size.  Growth Curve: The curve appears as a "J" shape. Initially, growth is slow, but it accelerates as the population increases, leading to a steep rise.  Characteristics: o Occurs when resources are unlimited. o Common in invasive species or populations recovering from a bottleneck. o Example: Bacteria in a nutrient-rich environment. 2. Logistic Growth (S-Curve)  Description: Logistic growth occurs when a population's growth rate decreases as it approaches the carrying capacity of its environment—the maximum population size that the environment can sustain.  Growth Curve: The curve resembles an "S" shape. It starts with a period of exponential growth, then slows down as resources become limited, eventually leveling off when carrying capacity is reached.  Characteristics: o Reflects real-world scenarios where resources are limited. o Stabilizes around the carrying capacity, with fluctuations due to environmental factors. o Example: Many animal populations in stable ecosystems, such as deer in a forest. 3. Cyclic Growth  Description: Some populations exhibit cyclic patterns of growth and decline, often influenced by environmental factors or interactions with other species (like predators or prey).  Growth Curve: The curve shows regular oscillations in population size.  Characteristics: o Fluctuations may correspond to seasonal changes or predator-prey dynamics. o Example: Snowshoe hares and lynx populations, where hare population increases lead to more food for lynxes, resulting in their population growth, followed by a decline in hares. 4. Irregular Growth  Description: Some populations may display irregular growth patterns due to unpredictable environmental changes, disease outbreaks, or other factors.  Growth Curve: The curve appears chaotic, with no discernible pattern.  Characteristics: o Often seen in populations affected by significant disturbances. o Example: Populations of some fish species can fluctuate widely due to changes in water temperature, pollution, or overfishing. Summary  Exponential Growth: Rapid increase with unlimited resources (J-Curve).  Logistic Growth: Growth slows as resources become limited, stabilizing at carrying capacity (S-Curve).  Cyclic Growth: Regular oscillations influenced by biotic or abiotic factors.  Irregular Growth: Unpredictable fluctuations due to various environmental pressures. Understanding these growth patterns helps ecologists and conservationists manage and predict population dynamics in different ecosystems. Highly developed and developing countries exhibit significant differences in various population characteristics. Here’s a breakdown of how they differ in terms of infant mortality rate, total fertility rate, replacement-level fertility, and age structure: 1. Infant Mortality Rate (IMR)  Highly Developed Countries: o Typically have low infant mortality rates, often below 5 deaths per 1,000 live births. o Improved healthcare, sanitation, and nutrition contribute to lower IMR.  Developing Countries: o Generally have higher infant mortality rates, often exceeding 30 deaths per 1,000 live births. o Factors include limited access to healthcare, poor maternal health, and inadequate nutrition. 2. Total Fertility Rate (TFR)  Highly Developed Countries: o Usually have low total fertility rates, often below the replacement level of 2.1 children per woman. o Contributing factors include access to contraception, education, career opportunities for women, and cultural shifts towards smaller families.  Developing Countries: o Typically have higher total fertility rates, often ranging from 3 to 6 children per woman. o Reasons include limited access to family planning, lower levels of education, and cultural norms favoring larger families. 3. Replacement-Level Fertility  Highly Developed Countries: o Often fall below the replacement-level fertility rate of 2.1, leading to aging populations and potential declines in total population size. o This can create challenges for social services and economic sustainability.  Developing Countries: o Usually have fertility rates above replacement level, contributing to population growth. o This can lead to youth bulges and increased demands on resources and services. 4. Age Structure  Highly Developed Countries: o Exhibit an aging population with a higher proportion of elderly individuals. The age structure often resembles a more rectangular shape. o This can result in higher dependency ratios and pressure on healthcare and pension systems.  Developing Countries: o Typically have a younger population with a larger proportion of children and adolescents. The age structure often resembles a pyramid. o This youthful demographic can lead to high potential for economic growth but also poses challenges in education and employment. Summary  Infant Mortality Rate: Lower in developed countries; higher in developing countries.  Total Fertility Rate: Low in developed countries; higher in developing countries.   Replacement-Level Fertility: Often below in developed countries; above in developing countries.  Age Structure: Aging population in developed countries; younger population in developing countries. These differences are crucial for understanding the social, economic, and health challenges faced by each type of country and can inform policy decisions related to healthcare, education, and economic development.