Chapter 4 Key Concepts

Ecology is the study of interactions between organisms and their environment and the effects of these interactions on the distribution and abundance of organisms.
Resources are materials whose availability or abundance may limit population growth.
Ecology is studied at many interacting hierarchical levels, including individual, population, species, community, and ecosystem.
Many ecological interactions occur between individuals and may be classified on a plus-minus-zero system depending on whether an individual benefits, suffers because of, or is not particularly affected by the interaction.
Territoriality is the maintenance of a home range that is defended.
Mobile and stationary predators search for prey using chemical, mechanical, and visual stimuli; some lure prey by using various “deceptions.”
Mobile predators may adjust their hunting behavior to optimize the rate of ingestion of prey.
Resistance to predators increases individual fitness and is therefore enhanced by natural selection.
Marine organisms avoid predators by means of crypsis, deceit, escape responses, and mimicry.
Many marine organisms can produce various morphologic features to discourage predator attacks (e.g., spines, strengthened skeletons, and other devices).
Many marine organisms are defended chemically by toxic organic compounds, acid secretions, and toxic metals.
Mechanical and chemical defenses against predation change in frequency with latitude, habitat, and oceanic basin.
Microhabitat can strongly affect a creature’s vulnerability to predators.
Commensal relationships benefit one species only. The benefit usually relates to food, substratum, or burrow space.
Mutualism is an evolved association among two or more species that benefits all participants.
Mutualism often reduces the risk of predation or disease or provides food for one member of the species pair.
Parasitism occurs when members of one species live at the expense of individuals of another species, without consuming the hosts totally as food and thereby killing them.
Parasites of invertebrates often affect the reproduction of the host.
Parasites often have complex life cycles that depend on more than one host species.
A population is a group of individuals that are affected by the same overall environment and are relatively unconnected with other populations of the same species.
Population change stems from survival, birth, death, immigration, and emigration.
Limiting resources may affect population growth.
Populations are often metapopulations, which are a series of interconnected subpopulations, some of which may contribute disproportionately large numbers of individuals to the metapopulation as a whole.
Spatial distribution is a measure of the spacing among individuals in a given area.
A population may show a regular change in density along a sampling line.
Many communities are organized around important structural aspects of the habitat or around foundation species that determine a great deal of the habitat structure.
Distribution and abundance of species populations in a community are determined by the combined effects of the following processes: (1) dispersal of larvae, spores, and adults; (2) competition; (3) predation and herbivory; (4) parasitism; (5) disturbance; and (6) facilitation.
Larval recruitment patterns strongly affect the species composition of marine communities.
Competition within and between species derives from the limiting resources of space and food.
Competition between species may involve direct displacement, preemption, or differential efficiency in the use of resources.
Competition has been demonstrated in marine communities by experimental removals of abundant species followed by expansions of competitors.
Competition combined with differential success in different microhabitats results in niche structure.
Some assemblages of natural species show extensive coexistence of presumed competitors despite apparent resource limitation.
Predation may prevent domination by a superior competitor and may strongly affect species composition.
Seasonal influxes of predators in shallow water and in the intertidal zone may devastate local communities.
Disturbance opens up space in the community. Its frequency may regulate long-term aspects of species composition in a habitat.
Species diversity may be maximized at intermediate levels of predation or disturbance.
Parasites are common and can affect their hosts by reduction in growth and reproduction or by enfeeblement.
Diseases in marine organisms are poorly understood, but they can cause swift population declines.
The role of disease must be verified by rigorous use of Koch’s principles, which involve identification of the pathogen, isolation, and successful experimental infection of the target organism.
Disease interacts strongly with changing environmental conditions and the increase of stressful physiological conditions of the host.
Target organisms may evolve resistance to disease, resulting in cycles of virulence in marine populations, which are poorly understood.
Succession is a predictable ordering of arrival and dominance of species, usually following a disturbance.
Succession may bring a community from one condition to another; however, other forces may also change community composition in a profound way, and local feedbacks may preserve the change.
The resilience of a community’s ecological structure should increase with the diversity of species that have important ecological roles, such as grazers or top predators.
Ecological interactions may be direct or indirect.
Indirect effects in communities can involve density- mediated indirect interactions or trait-mediated indirect interactions.
An ecosystem is a group of interdependent biological communities and abiotic factors in a single geographic area that are strongly interactive.
Nearly all ecosystems have primary producers (mainly photosynthetic), which are consumed by herbivores, which in turn are eaten by carnivores. Material escaping this cycle passes through the saprophyte cycle.
Some predatory species at the apex of food webs exert strong effects on the overall ecosystem.
Food webs may be controlled by top-down processes driven by top predators on lower trophic levels or by bottom-up processes.
Ecosystem studies usually account for the processes that affect movement of materials and energy through food webs and through the nonliving part of the ecosystem.
Ecosystem services are features and processes of ecosystems that benefit humanity, including biological productivity, provision of vital resources such as pure water, regulatory processes such as carbon processing, and cultural support such as parks. Quantification of services is useful.
Organism features can be explained based on a combination of genetic and nongenetic components.
Single genotypes may have the capacity to develop into distinctly different morphologies.
The geographic change in the frequency of genetic variants is called a cline.
New species usually originate after a species is divided by a geographic barrier.
Taxonomic classification involves successively nested grouping of species.
Characters can be used to construct trees of relationship. Taxa are grouped by means of shared evolutionary-derived characters.
DNA sequences are now used commonly to construct evolutionary trees.