Chapter 1

1.1 Ecological systems exist in a hierarchy of organization

• An ecological system may be an individual, population, species, community, ecosystem, landscape, or the entire biosphere.

Individuals

• Individual: living being—the most fundamental unit of ecology

  • every individual has a membrane, or other covering, across which it exchanges energy and materials with its environment.

  • an individual transforms energy and processes materials

  • it must acquire energy and nutrients from its surroundings and rid itself of unwanted products

• The individual approach to ecology emphasizes the way in which an individual’s morphology (the size and shape of its body), physiology, and behavior enable it to survive in its environment

  • Scientists using this approach also seek to understand why an organism in some environments but not in others

  • Ecologists who use the individual approach are often interested in adaptations

  • Adaptations: a characteristic of an organism that makes it well suited to its environment, the results of evolutionary change through the process of natural selection

Populations

• Population: individuals of the same species living in a particular area

  • ex. a population of catfish living in a pond, a population of maple trees living in Canda

  • Boundaries that determine a population: can be natural (where continent meets the ocean), or a political boundary (Canda vs US border)

• Populations have 5 distinct properties that are not exhibited by individuals

  • 1. Geographic range

    • Geographic range: also known as a population’s distribution, is the extent of land or water within which a population lives

  • 2. Abundance

    • Abundance: total number of individuals of a population living within a defined area

  • 3. Density

    • Density: the number of individuals per unit of area

  • 4. Change in size

    • Change in size: refers to increases and decreases in the number of individuals in an area over time

  • 5. Composition

    • Composition: describes the makeup of the population (ex: sex and age)

• The population approach to ecology examines variation over time and space in the number of individuals; the density of individuals; and the composition of individuals (includes sex ratio, the distribution of individuals among different age classes) and the genetic makeup of a population

  • Changes in the number of density of individuals can reflect the balance of births and deaths within a population, as well as immigration/emigration of individuals to and from a local population

Species

• Species: a group of organisms that can potentially interbreed naturally with each other and produce fertile offspring

  • but this definition does not fit all organisms on Earth

• Bacteria can also breed through horizontal gene transfer (which a bacterium engulfs genetic material from the environment)

Community

• Community: all populations of species living together in a particular area

  • some species eat other species, some have cooperative relationships, etc

  • may cover large area, maybe not

  • ecologists who study communities do not study every organism in the community

    • generally, they study a subset of the species in the community like the trees, insects, or birds

  • The boundaries that define a community are not always rigid

Ecosystem

• Ecosystem: one or more communities of living organisms interacting with their nonliving physical and chemical environments

  • in deep-sea vent, energy is acquired through chemosynthesis

  • dead organisms eaten by animals, eaten by other animals

The Landscape

• Landscape: multiple ecosystems that are connected by the movement of individuals, populations, matter, and energy

  • can include both aquatic and terrestrial ecosystems

  • includes patchwork of different communities, such as rainforest that have been logged in multiple locations

• The landscape approach is concerned with the movement of energy, matter, and individuals between different ecosystems

  • ex: how well different species of birds can move between patches of forests that are isolated in a landscape of agricultural fields

The Biosphere

• Biosphere: all the ecosystems and landscapes on Earth

  • distant ecosystems are linked together by exchanges of energy and nutrients carried by currents of wind and water and by the movements of organisms, such as migrating animals

  • ultimate ecological system

  • all transforms within in are internal with two exceptions: energy that enters from the Sun and energy lost to space

• The biosphere approach to ecology is concerned with the largest scale in the hierarchy of ecological systems

  • the movements of air and water, and the energy and chemical elements they contain, over Earth’s surface

1.2 Physical and biological principles govern ecological systems

• Ecological systems are governed by a few basic principles

  • Life builds on the physical properties and chemical reactions of matter

  • The diffusion of oxygen across surfaces, the rates of chemical reactions, the resistance of vessels to the flow of fluids, and the transmission of nerve impulses all obey the laws of thermodynamics

Conservation of Matter and Energy

• Law of conservation of matter: matter cannot be created or destroyed, but can only change form

• Law of conservation of energy: also known as the first law of thermodynamics, states that energy cannot be created or destroyed

These two laws imply that ecologists can track the movement of matter and energy as it is converted into new forms through organisms, populations, communities, ecosystems, and the biosphere.

Dynamic Steady Rates

• Dynamic steady state: when gains and losses are in balance in an ecological system

  • the principle of this applies to all levels of ecological organization

  • at the community level, the number of species living in a community decreases when a species becomes extinct and increases when a new species colonizers the area

Evolution

• To understand the variation among organism, we turn to the principle of evolution

• Phenotype: attribute of an organism like its behavior, morphology, or physiology

• Genotype: set of genes an organism carries with the environment in which it lives

• Over the history of life on Earth, the phenotypes of organisms have changed dramatically, given by the theory of evolution

  • Perhaps the best known process is evolution by natural selection, which is a change in the frequency of genes in a population through differential survival and reproduction of individuals that possess certain phenotypes

• Fitness: the survival and reproduction of an individual

• Species do not evolve in isolation

  • evolution in one species opens up new possibilities for other species with which the evolving species interacts

1.3 Different organisms play diverse roles in ecological systems

Categorizing Species Based on Sources of Energy

• Ecologists often categorize organisms according to how they obtain energy

  • Producers or autotrophs: organisms that use photosynthesis to convert solar energy into organic compounds

  • Consumers or heterotrophs: organisms that obtain their energy from other organisms

  • Mixtrophs: organisms that obtain their sources of carbon through a variety of ways from more than one source

Types of Species

Interspecific interactions

• Ecologists categorize species by the types of interactions they have with other species

  • Do they have a positive, negative, or neutral outcome on each member of a particular species?

Predation

• Predation: organisms that kill and partially or entirely consume another individual called the prey

• Parasitoids: an organism that lives within and consumes the tissues of a living host, eventually killing it

• Parasites: an organism that lives in or on another organism but rarely kills it

• Pathogen: a parasite that causes disease in its host

Herbivory

• Herbivores: organisms that consumes producers such as plants and algae

  • but they don’t destroy the whole plant

Competition

• Competition: an interaction resulting in negative effects between two species that depend on the same listing resource to survive, grow, and reproduce

Mutualism

• Mutualism: an interaction between two species in which each species receives benefits from the other

Commensalism

• Commensalism: an interaction in which two species live in close association and one species receives a benefit, while the other experiences neither a benefit nor a cost

• Symbiotic relationship: a close physical relationship between two different types of organisms is referred to as a symbiotic relationship

Consumers of Dead Organic Matter

• Scavenger: an organism that consumes dead animals

• Detritivore: an organism that feeds on dead organic matter and waste products that are collectively known as detritus

• Decomposer: organisms that break down dead organic material into simpler elements and compounds that can be recycled through the ecosystem

Habitat Versus Niche

• Habitat: the place, or physical setting, in which an organism lives

  • habitat distinctions rarely exist but the definition is useful

• Niche: the range of abiotic and biotic conditions it can tolerate

1.4 Scientists use several approaches to studying ecology

Testing Hypothesis With Manipulative Experiments

• Hypotheses can rarely be confirmed beyond a doubt

• Manipulative experiments can be designed where a hypothesis is tested by altering the factor that is hypothesized to be an underlying cause of the phenomenon

• Manipulation: the factor that we want to vary in an experiment. also known as Treatment

• Control: a manipulation that includes all aspects of an experiment except the factor of interest

• Experimental unit: the object to which we apply an experimental manipulation

• Replication: being able to produce a similar outcome multiple times

• Randomization: an aspect of experiment design in which every experimental unit has an equal chance of being assigned to a particular manipulation

• Microcosms: a simplified ecological system that attempts to replicate the essential features of an ecological system in a laboratory or field setting

Why Do We Calculate Means and Variances?

• Ecologists make observations, known as data

• We often want to know the average value or mean of the data

• Variance of the mean: a measurement that indicates the spread of data around the mean of a population when every member of the population has been measured

• Sample variance: a measurement that indicates the spread of data around the mean of a population when only a sample of the population has been measured

Alternative Approaches to Manipulative Experiments

• Natural experiment: an approach to hypothesis testing that relies on natural variation in the environment

• Mathematical model: a representation of a system with a set of equations that correspond to hypothesized relationships among the system’s components

1.5 Humans influence ecological systems

• Humans consume many resources, affecting the planet

• Biofuels: sources of fuel, such as corn

• Greenhouse gases are responsible for global warming, which is the increase in the average temperature of the planet due to an increased concentration of greenhouse gases in the atmosphere

• Greenhouse gases: compounds in the atmosphere that absorb the infared heat energy emitted by Earth and then emit some of the energy back toward Earth

The Role of Ecologists

• Ecologists increasingly realize that the only effective means of preserving the species of the world is through the conservation of ecosystems and the management of large-scale ecological processes