Ecology PART I

Lesson Objectives Describe ecological levels of organization in the biosphere. Distinguish between abiotic and biotic factors. Define organism, population, community, ecosystem, biome, and biosphere as the term are used in ecology and other ecological concepts. Identify factors that determine population growth rate. Compare and contrast exponential and logistic growth. Define limiting factors and their effect on population dynamics. Compare and contrast niches and habitats. Identify and describe terrestrial biomes. Give an overview of aquatic biomes. Describe characteristics of biotic and abiotic components of aquatic and terrestrial ecosystems

Introduction Ecology is the study of interactions of living things with each other and their environments.

Levels of Organization Ecologists study organisms and their environments at different levels of organization: Biosphere: consists of all organisms on Earth

Biome: group of ecosystems that have the same climate and dominant communities. Ecosystem: consists of living things and their environment.

Community: consists of populations of different species that live in the same area and interact together. Population: organisms of the same species that live in the same area, interact with one another, and produce fertile offspring.

Organisms: are individual living things. This is the lowest level of organization that ecologists study. Biologists study organisms, organ systems, organs, tissues, cells, organelles, and molecules. Chemists study atoms and subatomic particles.

Organisms and the Environment Organisms: life form consisting of one or more cells; has characteristics of life. Environment includes both living (biotic) and nonliving things (abiotic).

Biotic and Abiotic Factors Biotic living organisms Abiotic nonliving or physical factors Together determine productivity of the ecosystem in which organisms’ live

What Is a Population? In biology, a population is a group of organisms of the same species that live in the same area. How large a population is and how fast it is growing are often used as measures of its health.

Population Growth Rate Population growth rate (r) is how fast a population changes in size over time. A positive growth rate means a population is increasing. A negative growth rate means it is decreasing. The two main factors affecting population growth are the birth rate (b) and death rate (d).

Births and Deaths: Balancing Costs of Reproduction and Survival growth rate = birth rate – death rate r = b – d If birth rate exceeds death rate, r is positive and the population grows. If death rate exceeds birth rate, r is negative and the population declines. And if birth rate and death rate are in equilibrium, growth rate is zero, and the population remains stable. In a stable population, each individual, on the average, produces one offspring which survives long enough to reproduce itself. Mere survival is not success in the game of life; natural selection requires that survivors reproduce. Species vary in the strategies they use to achieve reproductive success, making trade-offs between the energy and time ‘‘costs” of survival and those of reproduction. Age at first reproduction, frequency of reproduction, number of offspring, parental care, reproductive lifespan, and offspring death rate are some of the traits which build strategies for successful reproduction.

Other Factors Affecting Population Growth Rate Population growth may also be affected by people coming into the population from somewhere else (immigration, i) or leaving the population for another area (emigration, e). The formula for population growth takes all these factors into account. r = (b + i) - (d + e) r = population growth rate; b = birth rate; i = immigration rate; d = death rate; and e = emigration rate

Patterns of Population Growth At first, exponentially then logistically until carrying capacity is reached No population can maintain exponential growth indefinitely. Inevitably, limiting factors such as reduced food supply or space lower birth rates, increase death rates, or lead to emigration, and lower the population growth rate. 1938, Pierre Verhulst derived a mathematical model of population growth which closely matches the S-curves observed under realistic conditions. In this logistic (S-curve) model, growth rate is proportional to the size of the population but also to the amount of available resources. At higher population densities, limited resources lead to competition and lower growth rates. Eventually, the growth rate declines to zero and the population becomes stable. The logistic model describes population growth for many populations in nature.

After 5 hours of exponential growth; one bacteria yields… 32,768

Limits to Population Growth limiting factor is a property of a population’s environment – living or nonliving – which controls the process of population growth. Biologists have identified two major types of limiting factors: Density-dependent factors Density-independent factors. Density-dependent limiting factors depend on population size and include competition, predation, parasitism, and disease. Density-independent limiting factors affect all populations regardless of population size and include unusual weather, natural disasters, seasonal cycles, and certain human activities, such as, damming rivers, and clear-cutting forests.

What Is a Community? Communities are made up of populations of different species. A community is the biotic part of an ecosystem. It consists of all the populations of all the species in the same area. It also includes their interactions.

What Is an Ecosystem? An ecosystem is a unit of nature and the focus of study in ecology. It consists of all the biotic and abiotic factors in an area and their interactions. Ecosystems can vary in size. A lake could be considered an ecosystem. So could a dead log on a forest floor. Both the lake and log contain a variety of species that interact with each other and with abiotic factors.

Ecosystem Components Niches Habitats Competitive Exclusion Principle

The Niche Niche organism’s occupation (role), where it lives, and way in which organism’s use conditions they exist in Food it eats Place in food web How it gets food Range of temperatures needed for survival When and how it reproduces No 2 species share the same niche or habitat, can occupy niches that are similar Habitat where an organism lives

The Habitat Physical environment to which an organisms has become adapted and survives in.

Competitive Exclusion Principle Two different species cannot occupy the same niche in the same geographic area. If they do they will compete with one another for the same food and other resources. Eventually, one species will out compete the other.

What Are Biomes? A biome is a group of similar ecosystems with the same general abiotic factors and primary producers. Biomes may be terrestrial or aquatic.

Terrestrial Biomes Terrestrial biomes include all the land areas on Earth where organisms live. The distinguishing features of terrestrial biomes are determined mainly by climate (abiotic factor). Terrestrial biomes include tundras, temperate forests and grasslands, chaparral, temperate and tropical deserts, and tropical forests and grasslands.

Terrestrial Biomes and Climate Climate is the average weather in an area over a long period of time. Weather refers to the conditions of the atmosphere from day to day. In terms of moisture, climates can be classified as arid (dry), semi-arid, humid (wet), or semi-humid. The amount of moisture depends on both precipitation and evaporation. Biomes are categorized based upon their climate types.

Climate and Biodiversity Climate determines plant growth, it also influences the number and variety of other organisms in a terrestrial biome. Biodiversity generally increases from the poles to the equator. It is also usually greater in more humid climates.

Climate and Adaptations Organisms evolve adaptations that help them survive in the climate of the biome where they live. For example, in biomes with arid climates, plants may have special tissues for storing water. The desert animals also have adaptations for a dry climate. In biomes with cold climates, plants may adapt by becoming dormant during the coldest part of the year. Dormancy is a state in which a plant slows down cellular activities and may shed its leaves. Animals also adapt to cold temperatures. One way is with insulation in the form of fur and fat.

Survey of Terrestrial Biomes Terrestrial biomes are classified by climatic factors and types of primary producers.

Aquatic Biomes Terrestrial organisms are generally limited by temperature and moisture. Therefore, terrestrial biomes are defined in terms of these abiotic factors. Most aquatic organisms do not have to deal with extremes of temperature or moisture. Instead, their main limiting factors are the availability of sunlight and the concentration of dissolved oxygen and nutrients in the water.

Aquatic Biomes and Sunlight In large bodies of standing water, including the ocean and lakes, the water can be divided into zones based on the amount of sunlight it receives: 1. The photic zone extends to a maximum depth of 200 meters; enough sunlight penetrates for algae and other photosynthetic organisms to photosynthesize. 2. The aphotic zone is water deeper than 200 meters; too little sunlight penetrates for photosynthesis to occur. As a result, food must be made by chemosynthesis or else drift down from the water above.

Aquatic Organisms Aquatic organisms generally fall into three broad groups: plankton, nekton, and benthos. They vary in how they move and where they live. 1. Plankton are tiny aquatic organisms that cannot move on their own. They live in the photic zone. They include phytoplankton and zooplankton. Phytoplankton are bacteria and algae that use sunlight to make food. Zooplankton are tiny animals that feed on phytoplankton. 2. Nekton are aquatic animals that can move on their own by ‘‘swimming” through the water. They may live in the photic or aphotic zone. They feed on plankton or other nekton. Examples of nekton include fish and shrimp. 3. Benthos are aquatic organisms that crawl in sediments at the bottom of a body of water. Many are decomposers. Benthos include sponges, clams, and anglerfish which are adapted to a life in the dark.

What Is the Biosphere? The biosphere is the global sum of all ecosystems; integrating all living beings and their relationships, including their interactions with the elements of the lithosphere, hydrosphere, and atmosphere.  

Lesson Summary Ecology is the study of how living things interact with each other and with their environment. The environment includes abiotic (nonliving) and biotic (living) factors. • Organisms are dependent upon their environments for energy and matter. • Population growth rate is how fast a population changes in size over time. It is determined by rates of birth, death, immigration, and emigration. • Under ideal conditions, populations can grow exponentially. The growth rate increases as the population gets larger. Most populations do not live under ideal conditions and grow logistically instead. Density-dependent factors slow population growth as population size nears the carrying capacity. • A community is the biotic part of an ecosystem. It consists of all the populations of all the species that live in the same area. It also includes their interactions. • An ecosystem consists of all the biotic and abiotic factors in an area and their interactions. A niche refers to the role of a species in its ecosystem. A habitat is the physical environment in which a species lives and to which it is adapted. Two different species cannot occupy the same niche in the same place for very long. • Terrestrial biomes are determined mainly by climate. Climate influences plant growth, biodiversity, and adaptations of land organisms. Terrestrial biomes include tundras, temperate forests and grasslands, chaparral, temperate and tropical deserts, and tropical forests and grasslands. • Aquatic biomes are determined mainly by sunlight and concentrations of dissolved oxygen and nutrients in the water. Aquatic organisms are plankton, nekton, or benthos. • The biosphere is composed of all the ecosystems on Earth.