Ecological Principles PDF

**Ecological Principles** Ecology is defined as the study of how organisms interact with one another and with their nonliving environment. The study of ecology involves various organisms, their lineage, and the characteristics of their habitat. An important aspect of ecology is understanding the ec...

**Ecological Principles** Ecology is defined as the study of how organisms interact with one another and with their nonliving environment. The study of ecology involves various organisms, their lineage, and the characteristics of their habitat. An important aspect of ecology is understanding the ecosystem and how it works. An ecosystem is a structural and functional unit of ecology where the living organisms interact with each other and the surrounding environment. In other words, an ecosystem is a chain of interactions between organisms and their environment. The term "Ecosystem" was first coined by A.G.Tansley, an English botanist, in 1935. **Structure of the Ecosystem** The structure of an ecosystem is characterized by the organization of both biotic and abiotic components. This includes the distribution of energy in our environment. It also includes the climatic conditions prevailing in that particular environment. The structure of an ecosystem can be split into two main components, namely: Biotic Components and Abiotic Components The biotic and abiotic components are interrelated in an ecosystem. It is an open system where the energy and components can flow throughout the boundaries. **1. Biotic Components** Biotic components refer to all living components in an ecosystem. Based on nutrition, biotic components can be categorized into autotrophs, heterotrophs and saprotrophs (or decomposers). **1.1 Tropic Levels and Ecosystem Chain** A **food chain** in an ecosystem is a series of production and consumption of energy. The chain can be described by its trophic levels. A trophic level is each step in the food chain in an ecosystem. **1.1.1** Producers include all autotrophs such as plants. They are called autotrophs as they can produce food through the process of photosynthesis. Consequently, all other organisms higher up on the food chain rely on producers for food. **1.1.2** **Consumers or heterotrophs** are organisms that depend on other organisms for food. Consumers are further classified into primary consumers, secondary consumers and tertiary consumers. **1.1.2.1 Primary consumers** are always herbivores as they rely on producers for food. **1.1.2.2 Secondary consumers** depend on primary consumers for energy. They can either be carnivores or omnivores. **1.1.2.3 Tertiary consumers** are organisms that depend on secondary consumers for food. Tertiary consumers can also be carnivores or omnivores. **1.1.2.4 Quaternary consumers** are present in some food chains. These organisms are prey on tertiary consumers for energy. Furthermore, they are usually at the top of a food chain as they have no natural predators. **1.1.3 Decomposers** include saprophytes such as fungi and bacteria. They directly thrive on the dead and decaying organic matter. Decomposers are essential for the ecosystem as they help in recycling nutrients to be reused by plants. **1.1 Tropic Levels and Ecosystem Chain** A **food web** is a complex network of interconnected food chains in an ecosystem, illustrating how energy and nutrients flow through various organisms. It highlights the relationships between producers, consumers, and decomposers, showing how they depend on each other for survival. Unlike a single food chain, a food web provides a more realistic representation of the multiple feeding relationships within a community. **Energy Production and Consumption** Producers, consumers, and decomposers undergo energy conversion processes for their own needs. One process is photosynthesis which described as the process by which plants use sunlight, water, and carbon dioxide to create oxygen and energy in the form of sugar. Its chemical equation is written as [6*CO*~2~ + 6*H*~2~*O* → *C*~6~*H*~12~*O*~6~ ]{.math.inline}which means reactants, carbon dioxide and water are converted by light energy captured by chlorophyll into sugar and oxygen. Some examples of photosynthetic bacteria include oxygenic cyanobacteria, anoxygenic green sulfur bacteria and anoxygenic green non-sulfur bacteria. These bacteria performed photosynthesis which uses carbon dioxide and water in the presence of sunlight to create glucose and oxygen. Early photosynthesizers like the cyanobacteria changed the early Earth\'s atmosphere to contain more oxygen. This environmental change allows for the evolution of oxygen-loving species, including humans, billions of years later. In contrast, **chemosynthesis** is the process by which certain microbes create energy by mediating reactions. Mostly those who belong to the producers category undergo chemosynthesis. Deep sea creatures such as mussels which reside and stay in seafloor hydrothermal vents are the usual chemosynthesis processors. Some specialized bacteria can convert simple inorganic compounds from their environment into more complex nutrient compounds without using sunlight, through chemosynthesis. **Cell Respiration** is a metabolic process by which cells break down glucose or other organic molecules to release energy, which is stored in the form of adenosine triphosphate (ATP). This energy is essential for various cellular activities, including growth, reproduction, and repair. **Key Stages of Cellular Respiration** **1. Glycolysis-** Occurs in the cytoplasm. Breaks down one molecule of glucose (6-carbon) into two molecules of pyruvate (3-carbon).Produces a net gain of 2 ATP and 2 NADH. **2. Pyruvate Oxidation (Link Reaction)-** Takes place in the mitochondrial matrix. Converts pyruvate into acetyl-CoA, releasing carbon dioxide (CO₂).Produces NADH. **3. Krebs Cycle (Citric Acid Cycle)-** Also occurs in the mitochondrial matrix.Acetyl-CoA is fully oxidized to CO₂.Produces 2 ATP, 6 NADH, and 2 FADH₂ per glucose molecule. **4. Electron Transport Chain (ETC) and Oxidative Phosphorylation** Located in the inner mitochondrial membrane. NADH and FADH₂ donate electrons to the ETC, which creates a proton gradient across the membrane. Protons flow back through ATP synthase, generating 34 ATP. Oxygen serves as the final electron acceptor, forming water. **Cell Respiration** C6​H12​O6​+6O2​→6CO2​+6H2​O+Energy (ATP) **Types of Cellular Respiration** **1. Aerobic Respiration-** Requires oxygen. Produces up to 36-38 ATP per glucose molecule. **2. Anaerobic Respiration-** Occurs in the absence of oxygen. Results in less ATP production (e.g., 2 ATP from glycolysis). End products may include lactic acid (in animals) or ethanol and CO₂ (in yeast and some plants). **Importance of Cellular Respiration** **Energy Production-** Provides ATP for cellular processes. **Metabolic Regulation-** Balances energy supply and demand. **Biochemical Pathways-** Links other metabolic pathways like photosynthesis and fermentation. It is ideal that energy balance exists among consumers. This balance is maintained through energy flow via food chain and nutrient cycling in the biosphere. The energy decreases as it is transferred into each step of the food chain. Each level in the chain consists of biomass, the dry weight of all organic matter contained in its organisms. The percentage of usable chemical energy transferred as biomass from one trophic level to the nest is called ecological efficiency. **2. Abiotic Components** Abiotic components are the non-living component of an ecosystem. It includes air, water, soil, minerals, sunlight, temperature, nutrients, wind, altitude, turbidity, etc. The nitrogen cycle is the natural process that moves nitrogen through the atmosphere, soil, water, and living organisms, ensuring this essential element is available for life. Nitrogen exists in the atmosphere as inert nitrogen gas (N₂), which is unusable by most organisms. Through nitrogen fixation, specialized bacteria and lightning convert atmospheric nitrogen into ammonia (NH₃) or ammonium (NH₄⁺), forms that plants can absorb. Plants take up these compounds and incorporate nitrogen into proteins and nucleic acids, which pass through the food chain as animals consume plants. When plants and animals die or excrete waste, decomposers (bacteria and fungi) break down organic matter, releasing ammonium in a process called ammonification. Ammonium can then undergo nitrification, where nitrifying bacteria convert it into nitrites (NO₂⁻) and then nitrates (NO₃⁻), which plants can reuse. Excess nitrates in the soil can be converted back to nitrogen gas by denitrifying bacteria through denitrification, completing the cycle. This cycle is critical for sustaining ecosystems and agricultural productivity. The sulfur cycle describes the movement of sulfur through the atmosphere, lithosphere, hydrosphere, and biosphere, playing a key role in protein synthesis and ecosystem balance. Sulfur is stored in rocks, minerals, and fossil fuels and is released into the environment through natural processes like volcanic eruptions, weathering of rocks, and decay of organic matter. Sulfate ions (SO₄²⁻) in the soil and water are absorbed by plants and converted into organic sulfur, which is passed through the food chain as animals consume plants. When organisms die or excrete waste, decomposers release sulfur back into the soil or water as hydrogen sulfide (H₂S) or sulfate. Some hydrogen sulfide is emitted into the atmosphere, where it reacts to form sulfur dioxide (SO₂) and then sulfate aerosols, which return to the Earth\'s surface via precipitation. Human activities, such as burning fossil fuels, release significant amounts of sulfur dioxide, contributing to acid rain and altering the natural cycle. This cycle is vital for ecosystems but is increasingly impacted by anthropogenic activities. The phosphorus cycle is the movement of phosphorus through the lithosphere, hydrosphere, and biosphere, essential for DNA, RNA, ATP, and cell membranes in living organisms. Unlike other biogeochemical cycles, it does not involve the atmosphere, as phosphorus typically exists as solid particles. Phosphorus is primarily stored in rocks and sediments as phosphate minerals (PO₄³⁻). Through weathering, these minerals release phosphates into the soil and water, where plants absorb them for growth. Animals acquire phosphorus by consuming plants or other animals, incorporating it into their bodies. When plants and animals die or excrete waste, decomposers return phosphorus to the soil or water as inorganic phosphates. These phosphates can be reabsorbed by plants or settle in sediments, eventually forming new rocks through geological processes over millions of years. Human activities, like mining phosphate rocks for fertilizers and detergents, and agricultural runoff, can lead to an excess of phosphorus in water bodies, causing eutrophication and disrupting aquatic ecosystems. The phosphorus cycle is crucial for maintaining soil fertility and ecosystem productivity. The carbon cycle is the process through which carbon moves among the atmosphere, biosphere, lithosphere, and hydrosphere, essential for regulating Earth\'s climate and supporting life. Carbon exists in the atmosphere primarily as carbon dioxide (CO₂), which plants absorb during photosynthesis to produce energy and biomass. Animals consume plants, incorporating carbon into their bodies, and release it back into the atmosphere through respiration as CO₂. When plants and animals die, decomposers break down organic matter, returning carbon to the soil or releasing it as CO₂ or methane (CH₄). Some organic material is buried over millions of years, forming fossil fuels like coal and oil. Combustion of these fuels by humans releases large amounts of CO₂ back into the atmosphere, disrupting the cycle. Additionally, carbon is exchanged between the atmosphere and oceans through diffusion, where it can be stored as dissolved CO₂ or used by marine organisms to build shells, eventually forming carbonates in sediments. The carbon cycle is vital for maintaining life and climate stability but is increasingly affected by human activities, leading to global warming and climate change. The water cycle, or hydrological cycle, is the continuous movement of water on, above, and below the Earth\'s surface. It begins with evaporation and transpiration, where water from oceans, lakes, and plants turns into water vapor due to the sun's heat. This vapor rises, cools, and undergoes condensation, forming clouds. When these droplets grow heavy, they fall as precipitation (rain, snow, sleet, or hail), replenishing water in rivers, lakes, and the ground. Some water infiltrates the soil, recharging groundwater, while the rest becomes runoff, flowing into larger bodies of water. Through percolation, water seeps deeper into aquifers, ensuring a sustainable supply. The cycle is vital for life, balancing ecosystems, and regulating climate. The rock cycle is a continuous process that transforms rocks through the Earth\'s internal heat and surface processes. It begins with igneous rocks, formed from cooled magma or lava. These rocks undergo weathering and erosion, breaking into sediments that accumulate and compact over time, forming sedimentary rocks. Under intense heat and pressure, sedimentary or igneous rocks transform into metamorphic rocks. If buried deeply, metamorphic rocks melt into magma, restarting the cycle. This process recycles Earth\'s materials, shaping landscapes and redistributing minerals essential for life and geological stability. **Function of Ecosystem** The functions of the ecosystem are as follows: 1\. It regulates the essential ecological processes, supports life systems and renders stability. 2\. It is also responsible for the cycling of nutrients between biotic and abiotic components. 3\. It maintains a balance among the various trophic levels in the ecosystem. 4\. It cycles the minerals through the biosphere. 5\. The abiotic components help in the synthesis of organic components that involve the exchange of energy. These functions describe the dynamic processes that occur within an ecosystem, driving the transfer of energy, recycling of nutrients, and production of biomass. **Functional Aspect of Ecosystem** **1. Productivity.** Refers to the rate at which biomass is produced in an ecosystem, primarily by producers. It includes primary productivity (by plants and algae) and secondary productivity (by consumers). **2. Energy Flow.** Describes the transfer of energy through different trophic levels, from producers to consumers to decomposers, following the laws of thermodynamics. This energy flow is unidirectional, with energy entering as sunlight and exiting primarily as heat. **3. Decomposition.** Involves the breakdown of dead organic matter by decomposers (such as bacteria and fungi), which releases nutrients back into the soil, making them available for plants and other organisms. **4. Nutrient Cycling.** Refers to the cyclical movement of nutrients (such as nitrogen, carbon, and phosphorus) within the ecosystem, ensuring that these essential elements are reused and maintained within the system. **Population Ecology** Ecology is a sub-discipline of biology that studies the interactions between organisms and their environments. A group of interbreeding individuals (individuals of the same species) living and interacting in a given area at a given time is defined as a **population**. These individuals rely on the same resources and are influenced by the same environmental factors. **Population ecology**, therefore, is the study of how individuals of a particular species interact with their environment and change over time. The study of any population usually begins by determining how many individuals of a particular species exist, and how closely associated they are with each other. Within a particular habitat, a population can be characterized by its population size (N), defined by the total number of individuals, and its population density, the number of individuals of a particular species within a specific area or volume (units are number of individuals/unit area or unit volume). Population size and density are the two main characteristics used to describe a population. For example, larger populations may be more stable and able to persist better than smaller populations because of the greater amount of genetic variability, and their potential to adapt to the environment or to changes in the environment. On the other hand, a member of a population with low population density (more spread out in the habitat), might have more difficulty finding a mate to reproduce compared to a population of higher density. Other characteristics of a population include dispersion - the way individuals are spaced within the area; age structure - number of individuals in different age groups and; sex ratio - proportion of males to females; and growth - change in population size (increase or decrease) over time. Populations change over time and space as individuals are born or immigrate (arrive from outside the population) into an area and others die or emigrate (depart from the population to another location). Populations grow and shrink and the age and gender composition also change through time and in response to changing environmental conditions. Some populations, for example trees in a mature forest, are relatively constant over time while others change rapidly. Using idealized models, population ecologists can predict how the size of a particular population will change over time under different conditions. **Exponential Growth** Charles Darwin, in his theory of natural selection, was greatly influenced by the English clergyman Thomas Malthus. Malthus published a book (An Essay on the Principle of Population) in 1798 stating that populations with unlimited natural resources grow very rapidly. According to the Malthus\' model, once population size exceeds available resources, population growth decreases dramatically. This accelerating pattern of increasing population size is called exponential growth, meaning that the population is increasing by a fixed percentage each year. When plotted (visualized) on a graph showing how the population size increases over time, the result is a J-shaped curve. Each individual in the population reproduces by a certain amount (r) and as the population gets larger, there are more individuals reproducing by that same amount (the fixed percentage). In nature, exponential growth only occurs if there are no external limits. The \"J\" shaped curve of exponential growth for a hypothetical population of bacteria. The population starts out with 100 individuals and after 11 hours there are over 24,000 individuals. As time goes on and the population size increases, the rate of increase also increases (each step up becomes bigger). In this figure \"r\" is positive. This type of growth can be represented using a mathematical function known as the exponential growth model: [**G** **=** **rN**]{.math.inline} also expressed in [\$\\frac{\\mathbf{\\text{dN}}}{\\mathbf{\\text{dt}}}\\mathbf{= rN}\$]{.math.inline}. In this equation [\$\\mathbf{\\text{G\~or}}\\frac{\\mathbf{\\text{dN}}}{\\mathbf{\\text{dt}}}\$]{.math.inline} is the population growth rate, it is a measure of the number of individuals added per time interval time. [**r**]{.math.inline} is the per capita rate of increase (the average contribution of each member in a population to the population growth; per capita means \"per person\"). [**N**]{.math.inline} is the population size, the number of individuals in the population at a particular time. **Per capita rate of increase (r)** In exponential growth, the population growth rate (***G***) depends on population size (***N***) and the per capita rate of increase (***r***). In this model ***r*** does not change (fixed percentage) and change in population growth rate, ***G***, is due to change in population size, ***N***. As new individuals are added to the population, each of the new additions contribute to population growth at the same rate (***r***) as the individuals already in the population. r = (birth rate + immigration rate) - (death rate and emigration rate). If r is positive (\> zero), the population is increasing in size; this means that the birth and immigration rates are greater than death and emigration. If r is negative (\< zero), the population is decreasing in size; this means that the birth and immigration rates are less than death and emigration rates. If r is zero, then the population growth rate (G) is zero and population size is unchanging, a condition known as zero population growth. \"r\" varies depending on the type of organism, for example a population of bacteria would have a much higher \"r\" than an elephant population. In the exponential growth model r is multiplied by the population size, N, so population growth rate is largely influenced by N. This means that if two populations have the same per capita rate of increase (r), the population with a larger N will have a larger population growth rate than the one with a smaller N. **Logistic Growth** Exponential growth cannot continue forever because resources (food, water, shelter) will become limited. Exponential growth may occur in environments where there are few individuals and plentiful resources, but soon or later, the population gets large enough that individuals run out of vital resources such as food or living space, slowing the growth rate. When resources are limited, populations exhibit logistic growth. In logistic growth a population grows nearly exponentially at first when the population is small and resources are plentiful but growth rate slows down as the population size nears limit of the environment and resources begin to be in short supply and finally stabilizes (zero population growth rate) at the maximum population size that can be supported by the environment (carrying capacity). This results in a characteristic S-shaped growth curve. The mathematical function or logistic growth model is represented by the following equation: [\$G = rN\\left( 1 - \\frac{N}{K} \\right)\$]{.math.inline}, where K is the carrying capacity - the maximum population size that a particular environment can sustain (\"carry\"). Notice that this model is similar to the exponential growth model except for the addition of the carrying capacity. In the exponential growth model, population growth rate was mainly dependent on N so that each new individual added to the population contributed equally to its growth as those individuals previously in the population because per capita rate of increase is fixed. In the logistic growth model, individuals\' contribution to population growth rate depends on the amount of resources available (K). As the number of individuals (N) in a population increases, fewer resources are available to each individual. As resources diminish, each individual on average, produces fewer offspring than when resources are plentiful, causing the birth rate of the population to decrease. Shows logistic growth of a hypothetical bacteria population. The population starts out with 10 individuals and then reaches the carrying capacity of the habitat which is 500 individuals. Influence of K on population growth rate In the logistic growth model, the exponential growth (r \* N) is multiplied by fraction or expression that describes the effect that limiting factors (1 - N/K) have on an increasing population. Initially when the population is very small compared to the capacity of the environment (K), 1 - N/K is a large fraction that nearly equals 1 so population growth rate is close to the exponential growth (r \* N). For example, supposing an environment can support a maximum of 100 individuals and N = 2, N is so small that 1 - N/K (1 - 2/100 = 0.98) will be large, close to 1. As the population increases and population size gets closer to carrying capacity (N nearly equals K), then 1 - N/K is a small fraction that nearly equals zero and when this fraction is multiplied by r \* N, population growth rate is slowed down. In the earlier example, if the population grows to 98 individuals, which is close to (but not equal) K, then 1 - N/K (1 - 98/100 = 0.02) will be so small, close to zero. If population size equals the carrying capacity, N/K = 1, so 1 - N/K = 0, population growth rate will be zero (in the above example, 1 - 100/100 = 0). This model, therefore, predicts that a population\'s growth rate will be small when the population size is either small or large, and highest when the population is at an intermediate level relative to K. At small populations, growth rate is limited by the small amount of individuals (N) available to reproduce and contribute to population growth rate whereas at large populations, growth rate is limited by the limited amount of resources available to each of the large number of individuals to enable them reproduce successfully. In fact, maximum population growth rate (G) occurs when N is half of K. Yeast is a microscopic fungus, used to make bread and alcoholic beverages, that exhibits the classical S-shaped logistic growth curve when grown in a test tube. Its growth levels off as the population depletes the nutrients that are necessary for its growth. In the real world, however, there are variations to this idealized curve. For example, a population of harbor seals may exceed the carrying capacity for a short time and then fall below the carrying capacity for a brief time period and as more resources become available, the population grows again. This fluctuation in population size continues to occur as the population oscillates around its carrying capacity. Still, even with this oscillation, the logistic model is exhibited. 1\. At the beginning of the year, there are 7650 individuals in a population of beavers whose per capita rate of increase for the year is 0.18. What is its population growth rate at the end of the year? \ [**G** **=** **0.18(7650)**]{.math.display}\ \ [**G** **=** **1377** **individuals**]{.math.display}\ So, the population growth rate at the end of the year for the beavers is 1377 individuals. 2\. A zebrafish population of 1000 individuals lives in an ecosystem that can support a maximum of 2000 zebrafish. The per capita rate of increase for the population is 0.01 for the year. What is the population growth rate? \ [\$\$\\mathbf{G = rN}\\left( \\mathbf{1 -}\\frac{\\mathbf{N}}{\\mathbf{K}} \\right)\$\$]{.math.display}\ \ [\$\$\\mathbf{G = 0.01(1000)}\\left( \\mathbf{1 -}\\frac{\\mathbf{1000}}{\\mathbf{2000}} \\right)\$\$]{.math.display}\ \ [**G** **=** **5**]{.math.display}\ So, the population growth rate for the zebrafish is 5 individuals. **Factors limiting population growth** Recall previously that we defined density as the number of individuals per unit area. In nature, a population that is introduced to a new environment or is rebounding from a catastrophic decline in numbers may grow exponentially for a while because density is low and resources are not limiting. Eventually, one or more environmental factors will limit its population growth rate as the population size approaches the carrying capacity and density increases. Example: imagine that in an effort to preserve elk, a population of 20 individuals is introduced to a previously unoccupied island that\'s 200 [km^2^]{.math.inline} in size. The population density of elk on this island is 0.1 elk/ [km^2^]{.math.inline} (or 10 [km^2^]{.math.inline} for each individual elk). As this population grows (depending on its per capita rate of increase), the number of individuals increases but the amount of space does not so density increases. Suppose that 10 years later, the elk population has grown to 800 individuals, density = 4 elk/ [km^2^]{.math.inline} (or 0.25 [km^2^]{.math.inline} for each individual). The population growth rate will be limited by various factors in the environment. For example, birth rates may decrease due to limited food or death rate increase due to rapid spread of disease as individuals encounter one another more often. This impact on birth and death rate in turn influences the per capita rate of increase and how the population size changes with changes in the environment. When birth and death rates of a population change as the density of the population changes, the rates are said to be density-dependent and the environmental factors that affect birth and death rates are known as density-dependent factors. In other cases, populations are held in check by factors that are not related to the density of the population and are called density-independent factors and influence population size regardless of population density. Conservation biologists want to understand both types because this helps them manage populations and prevent extinction or overpopulation. The density of a population can enhance or diminish the impact of density-dependent factors. Most density-dependent factors are biological in nature (biotic), and include such things as predation, inter- and intraspecific competition for food and mates, accumulation of waste, and diseases such as those caused by parasites. Usually, higher population density results in higher death rates and lower birth rates. For example, as a population increases in size food becomes scarcer and some individuals will die from starvation meaning that the death rate from starvation increases as population size increases. Also as food becomes scarcer, birth rates decrease due to fewer available resources for the mother meaning that the birth rate decreases as population size increases. For density-dependent factors, there is a feedback loop between population density and the density-dependent factor. Two examples of density-dependent regulation. First one is showing results from a study focusing on the giant intestinal roundworm (Ascaris lumbricoides), a parasite that infects humans and other mammals. Denser populations of the parasite exhibited lower fecundity (number of eggs per female). One possible explanation for this is that females would be smaller in more dense populations because of limited resources and smaller females produce fewer eggs. Density-independent birth rates and death rates do NOT depend on population size; these factors are independent of, or not influenced by, population density. Many factors influence population size regardless of the population density, including weather extremes, natural disasters (earthquakes, hurricanes, tornadoes, tsunamis, etc.), pollution and other physical/abiotic factors. For example, an individual deer may be killed in a forest fire regardless of how many deer happen to be in the forest. The forest fire is not responding to deer population size. As the weather grows cooler in the winter, many insects die from the cold. The change in weather does not depend on whether there is a population size of 100 mosquitoes or 100,000 mosquitoes, most mosquitoes will die from the cold regardless of the population size and the weather will change irrespective of mosquito population density. Looking at the growth curve of such a population would show something like an exponential growth followed by a rapid decline rather than levelling off. In real-life situations, density-dependent and independent factors interact. For example, a devastating earthquake occurred in Haiti in 2010. This earthquake was a natural geologic event that caused a high human death toll from this density-independent event. Then there were high densities of people in refugee camps and the high density caused disease to spread quickly, representing a density-dependent death rate. 1\. At the beginning of the year, a wildlife area that is 1,000,000 ha in size has a population of 90 Brown bears with a per capita growth rate of 0.02. It\'s estimated that brown bears need a territory of about 10 km2 per individual (note: 1 km2 = 100 ha). Use this information to answer the following questions. a\. What is the density of brown bears in this wildlife preserve currently? b\. What is the carrying capacity of the preserve? c\. What is the population growth rate for this year? 2\. A wildlife ranch currently has a population of polar bears whose death rate is 0.05 and birth rate is 0.12 per year. This particular ranch is isolated from other suitable habitats so there\'s no immigration into or emigration from this population. This population is experiencing logistic growth and currently has 550 bears. If the population growth rate for the year was 36 bears, what is the carrying capacity of the preserve? 1\. At the beginning of the year, a wildlife area that is 1,000,000 ha in size has a population of 90 Brown bears with a per capita growth rate of 0.02. It\'s estimated that brown bears need a territory of about 10 km2 per individual (note: 1 km2 = 100 ha). Use this information to answer the following questions. a\. What is the density of brown bears in this wildlife preserve currently? -Density is calculated by dividing the population size by the area available. However, we need to convert the area of the wildlife preserve into the same unit used for the territory of each brown bear. -The wildlife preserve area is 1,000,000 hectares (ha). -1 km² = 100 ha, so the area of the preserve in km² is: -Area in km²=1001,000,000ha​=10,000km² [\$\\mathbf{Density =}\\frac{\\mathbf{\\text{Population}}}{\\mathbf{\\text{Area}}}\$]{.math.inline}**​** \ [\$\$\\mathbf{Density =}\\frac{\\mathbf{90\\ bears}}{\\mathrm{10,000km²}}\$\$]{.math.display}\ [\$\\mathbf{Density =}\\frac{\\mathbf{90}}{\\mathrm{10,000}}\$]{.math.inline} **bears per km²** So, the density of brown bears in the preserve is 0.009 bears per km². b\. What is the carrying capacity of the preserve? -The carrying capacity refers to the maximum population that can be supported by the available habitat. We know that each brown bear needs a territory of 10 km². -To find the carrying capacity, we divide the total area of the preserve by the area needed by each bear: \ [\$\$\\mathbf{Carrying\\ Capacity =}\\frac{\\mathbf{\\text{Total\~Area}}}{\\mathbf{\\text{Area\~per\~Bear}}}\$\$]{.math.display}\ \ [\$\$\\mathbf{Carrying\\ Capacity =}\\frac{\\mathbf{10000}\\mathrm{km²}}{\\mathbf{10}\\mathrm{km²}}\$\$]{.math.display}\ \ [**Carrying** **Capacity=1000**bears]{.math.display}\ So, the carrying capacity of the preserve is 1,000 bears. c\. What is the population growth rate for this year? Since, it provides a constant per capita growth rate (***r***), and it does not suggest the population is affected by resource limits or nearing carrying capacity. Therefore, we will use the exponential growth rate, \ [**G** **=** **rN**]{.math.display}\ \ [**G** **=** **0.02(90)**]{.math.display}\ [**G** **=** **1.8**]{.math.inline} **or 2 individuals** Since we are counting individual bears, we round to the nearest whole number because populations are expressed in whole individuals: So, the population growth rate for the bears is 2 individuals. 2\. A wildlife ranch currently has a population of polar bears whose death rate is 0.05 and birth rate is 0.12 per year. This particular ranch is isolated from other suitable habitats so there\'s no immigration into or emigration from this population. This population is experiencing logistic growth and currently has 550 bears. If the population growth rate for the year was 36 bears, what is the carrying capacity of the preserve? \ [*r* = *Birth* *rate* − *Death* *rate* = 0.12 − 0.05 = 0.07*per* *year*]{.math.display}\ \ [\$\$\\mathbf{\\ \\ G = rN}\\left( \\mathbf{1 -}\\frac{\\mathbf{N}}{\\mathbf{K}} \\right)\$\$]{.math.display}\ \ [\$\$\\mathbf{36 = 0.07(550)}\\left( \\mathbf{1 -}\\frac{\\mathbf{550}}{\\mathbf{K}} \\right)\$\$]{.math.display}\ \ [\$\$\\mathbf{36 = 38.5}\\left( \\mathbf{1 -}\\frac{\\mathbf{550}}{\\mathbf{K}} \\right)\$\$]{.math.display}\ \ [\$\$\\frac{\\mathbf{36}}{\\mathbf{38.5}}\\mathbf{=}\\frac{\\mathbf{38.5}\\left( \\mathbf{1 -}\\frac{\\mathbf{550}}{\\mathbf{K}} \\right)}{\\mathbf{38.5}}\$\$]{.math.display}\ \ [\$\$\\frac{\\mathbf{36}}{\\mathbf{\\ \\ \\ 38.5}}\\mathbf{= 1 -}\\frac{\\mathbf{550}}{\\mathbf{K}}\$\$]{.math.display}\ \ [\$\$\\mathbf{\\text{\~\~\~\~\~}}\\frac{\\mathbf{550}}{\\mathbf{K}}\\mathbf{=}\\mathbf{1 -}\\frac{\\mathbf{36}}{\\mathbf{38.5}}\$\$]{.math.display}\ \ [\$\$\\frac{\\mathbf{550}}{\\mathbf{K}}\\mathbf{=}\\frac{\\mathbf{38.5}}{\\mathbf{38.5}}\\mathbf{-}\\frac{\\mathbf{36}}{\\mathbf{38.5}}\$\$]{.math.display}\ \ [\$\$\\mathbf{\\text{\~\~\~\~\~\~\~\~\~}}\\frac{\\mathbf{550}}{\\mathbf{K}}\\mathbf{=}\\frac{\\mathbf{2.5}}{\\mathbf{38.5}}\\mathbf{\\ }\$\$]{.math.display}\ \ [       **2.5K** **=** **38.5(550)**]{.math.display}\ \ [\$\$\\mathbf{\\text{\~\~\~\~\~\~\~}}\\frac{\\mathbf{2.5}\\mathbf{K}}{\\mathbf{2.5}}\\mathbf{=}\\frac{\\mathbf{38.5(550)}\\mathrm{\\ }}{\\mathbf{2.5}}\\mathbf{\\text{\~\~\~\~\~\~\~\~\~\~\~\~\~}}\$\$]{.math.display}\ The carrying capacity of the preserve is approximately 8,470 bears **Life Tables and Survivorship** Population ecologists use life tables to study species and identify the most vulnerable stages of organisms\' lives to develop effective measures for maintaining viable populations. Life tables track survivorship, the chance of an individual in a given population surviving to various ages. Life tables were invented by the insurance industry to predict how long, on average, a person will live. Biologists use a life table as a quick window into the lives of the individuals of a population, showing how long they are likely to live, when they\'ll reproduce, and how many offspring they\'ll produce. Life tables are used to construct survivorship curves, which are graphs showing the proportion of individuals of a particular age that are now alive in a population. Survivorship (chance of surviving to a particular age) is plotted on the y-axis as a function of age or time on the x-axis. However, if the percent of maximum lifespan is used on the x-axis instead of actual ages, it is possible to compare survivorship curves for different types of organisms. All survivorship curves start along the y-axis intercept with all of the individuals in the population (or 100% of the individuals surviving). As the population ages, individuals die and the curves goes down. A survivorship curve never goes up. Life Table for the U.S. population in 2011 showing the number who are expected to be alive at the beginning of each age interval based on the death rates in 2011. For example, 95,816 people out of 100,000 are expected to live to age 50 (0.983 chance of survival). The chance of surviving to age 60 is 0.964 but the chance of surviving to age 90 is only 0.570. Survivorship curves reveal a huge amount of information about a population, such as whether most offspring die shortly after birth or whether most survive to adulthood and likely to live long lives. They generally fall into one of three typical shapes, Types I, II and III.Organisms that exhibit **Type I survivorship** curves have the highest probability of surviving every age interval until old age, then the risk of dying increases dramatically. Humans are an example of a species with a Type I survivorship curve. Others include the giant tortoise and most large mammals such as elephants. These organisms have few natural predators and are, therefore, likely to live long lives. They tend to produce only a few offspring at a time and invest significant time and effort in each offspring, which increases survival. In the Type III survivorship curve most of the deaths occur in the youngest age groups. Juvenile survivorship is very low and many individuals die young but individuals lucky enough to survive the first few age intervals are likely to live a much longer time. Most plants species, insect species, frogs as well as marine species such as oysters and fishes have a Type III survivorship curve. A female frog may lay hundreds of eggs in a pond and these eggs produce hundreds of tadpoles. However, predators eat many of the young tadpoles and competition for food also means that many tadpoles don\'t survive. But the few tadpoles that do survive and metamorphose into adults then live for a relatively long time (for a frog). The mackerel fish, a female is capable of producing a million eggs and on average only about 2 survive to adulthood. Organisms with this type of survivorship curve tend to produce very large numbers of offspring because most will not survive. They also tend not to provide much parental care, if any. Type II survivorship is intermediate between the others and suggests that such species have an even chance of dying at any age. Many birds, small mammals such as squirrels, and small reptiles, like lizards, have a Type II survivorship curve. The straight line indicates that the proportion alive in each age interval drops at a steady, regular pace. The likelihood of dying in any age interval is the same. In reality, most species don\'t have survivorship curves that are definitively type I, II, or III. They may be anywhere in between. These three, though, represent the extremes and help us make predictions about reproductive rates and parental investment without extensive observations of individual behavior. For example, humans in less industrialized countries tend to have higher mortality rates in all age intervals, particularly in the earliest intervals when compared to individuals in industrialized countries. Looking at the population of the United States in 1900. you can see that mortality was much higher in the earliest intervals and throughout, the population seemed to exhibit a type II survivorship curve, similar to what might be seen in less industrialized countries or amongst the poorest populations. The human population is growing rapidly. For most of human history, there were fewer than 1 billion people on the planet. During the time of the agricultural revolution, 10,000 B.C., there were only 5-10 million people on Earth - which is basically the population of New York City today. In 1800, when the Industrial Revolution began, there were approximately 1 billion people on Earth. We\'ve added 6 billion people to the human population in just a little over 200 years. This demonstrates the capacity of the human population to exhibit exponential growth. **The human population** **Demography** applies the principles of population ecology to the human population. Demographers study how human populations grow, shrink, and change in terms of age and gender compositions. Demographers also compare populations in different countries or regions. One of the tools that demographers use to understand populations is the age structure diagram. This diagram shows the distribution by ages of females and males within a certain population in graphic. An age-structure diagram provides a snapshot of the current population and can represent information about the past and give potential clues about future problems. When you are interpreting age-structure diagrams, it is important to compare the width of the base to the rest of the population. If the base is very wide compared to the upper parts of the diagram, then this indicates a lot of young people (pre-reproductive) in the population compared to older generations i.e. a high birth rate and a rapidly growing population. If the base is smaller than the upper parts of the diagram, then this indicates few young people in the population compared to older generations (post-reproductive). This population has low birth rates and is shrinking. The demographic transition model shows the changes in the patterns of birth rates and death rates that typically occur as a country moves through the process of industrialization or development. The demographic transition model was built based on patterns observed in European counties as they were going through industrialization. This model can be applied to other countries, but not all countries or regions fit the model exactly. And the pace or rate at which a country moves through the demographic transition varies among countries. In the demographic transition model, a country begins in Stage 1, the preindustrial stage. In Stage 1 both birth rates and death rates are high. The high death rates are because of disease and potential food scarcity. A country in Stage 1 of the demographic transition model does not have good health care; there may not be any hospitals or doctors. Children are not vaccinated against common diseases and therefore many children die at a young age. Infant and childhood mortality rates (death rates) are very high. A society in Stage 1 is likely based upon agriculture and most people grow their own food. Therefore, droughts or flood can lead to widespread food shortages and death from famine. All of these factors contribute to the high death rate in Stage 1. Partly to compensate for the high death rates, birth rates are also high. High birth rates mean that families are large and each couple, on average, has many children. When death rates are high, having many children means that at least one or two will live to adulthood. In Stage 1, children are an important part of the family workforce and are expected to work growing food and taking care of the family. As you are examining the stages of the demographic transition model, remember that: Population Growth Rate = Birth Rate - Death Rate In Stage 1, birth rates are high, but death rates are high as well. Therefore, population growth rate is low or close to zero. As a country develops, medical advances are made such as access to antibiotics and vaccines. Sanitation improvements, such as proper waste and sewage disposal, and water treatment for clean drinking water also progress. Food production also increases. Together these changes lead to falling death rates which marks the beginning of Stage 2. Death rates continue to fall throughout Stage 2 as conditions improve. This means that people are living longer and childhood morality drops. However, birth rates are still high in Stage 2. There is a time lag between the improving conditions and any subsequent changes in family size, so women are still having many children and now more of these children are living into adulthood. In Stage 2, the birth rate is higher than the death rate, so population growth rate is high. This means that population size increases greatly during Stage 2 of the demographic transition model. A falling birth rate marks the beginning of Stage 3 in the demographic transition model. As a country continues to industrialize, many women join the workforce. Additionally, raising children becomes more expensive and children no longer work on the family farm or make large economic contributions to the family. Individuals may have access to birth control and choose to have fewer children. This leads to a drop in birth rates and smaller family sizes. Death rates also continue to drop during Stage 3 as medicine, sanitation and food security continue to improve. Even though both birth rates and death rates are falling throughout Stage 3, birth rates are higher than death rates. This means that population growth rate is high and that population size continues to increase in Stage 3 of the demographic transition model. Birth rate and death rates drop to low, stable, approximately equal levels in Stage 4. Death rates are low because of medical advances, good sanitation, clean drinking water and food security. Birth rates are low because of access to birth control and many women delay having their first child until they have worked. Childhood mortality is low, life expectancy is high, and family size is approximately two children per couple. With low birth rates and low death rates, population growth rate is approximately zero in Stage 4. This figure repeats the demographic transition model, with the changes in population size (y-axes on the far right) shown by the black line. Population size is low and stable in Stage 1, increases rapidly in Stage 2 and 3 because birth rates are higher than death rates, and then is high and stable again in Stage 4. Life expectancy is the average number of years that a person in a particular population is expected to live. Life expectancy at birth is the number of years a newborn infant would live if mortality rates at the time of its birth did not change. For example, the life expectancy at birth for someone born in 2014 in Japan is 84.46 years while the life expectancy at birth for someone born in the United States in 2014 is 79.56 years Life expectancy is the average number of years that a person in a particular population is expected to live. Life expectancy at birth is the number of years a newborn infant would live if mortality rates at the time of its birth did not change. For example, the life expectancy at birth for someone born in 2014 in Japan is 84.46 years while the life expectancy at birth for someone born in the United States in 2014 is 79.56 years. As a country moves through the demographic transition model, life expectancy increases. Overall, life expectancy has increased for most countries and regions over the past 100 years. However, there is still a significant amount of variation in life expectancy in different regions of the world. Fertility is the actual level of reproduction of a population per individual, based on the number of live births that occur. Total fertility is the average number of children born to each woman, over the woman\'s lifespan, in a population. Birth rate and fertility are closely linked terms. As a country moves through the demographic transition model, fertility rates decrease. Overall, fertility rates have decreased for most countries and regions over the past 50. However, there is still a significant amount of variation among different regions of the world.