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Related Concept Videos

Contact-dependent Signaling01:19

Contact-dependent Signaling

Contact-dependent signaling, as the name suggests, requires that communicating cells be in direct contact with each other. This is achieved either through receptor-ligand interactions or by specialized cytoplasmic channels that allow the flow of small molecules between cells. In animal cells, channels called gap junctions facilitate contact-dependent signaling in certain tissues, whereas, plasmodesmata perform a similar function in plants.
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In most cases, excessive hormone production is prevented by negative feedback—a loop that starts with a stimulus inducing the release of a particular substance, like a hormone, to maintain a certain level before triggering a signal that results in a decrease in further release of the hormone.
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Population Growth00:57

Population Growth

Population size is dynamic, increasing with birth rates and immigration, and decreasing with death rates and emigration. In ideal conditions with unlimited resources, populations can increase exponentially, which plots as a J-shaped growth rate curve of population size against time. This type of curve is characteristic of newly-introduced invasive species, or populations that have suffered catastrophic declines and are rebounding.
Hardy-Weinberg Principle01:49

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Diploid organisms have two alleles of each gene, one from each parent, in their somatic cells. Therefore, each individual contributes two alleles to the gene pool of the population. The gene pool of a population is the sum of every allele of all genes within that population and has some degree of variation. Genetic variation is typically expressed as a relative frequency, which is the percentage of the total population that has a given allele, genotype or phenotype.

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Related Experiment Video

Updated: May 7, 2026

Live-3D-Cell Immunocytochemistry Assays of Pediatric Diffuse Midline Glioma
09:06

Live-3D-Cell Immunocytochemistry Assays of Pediatric Diffuse Midline Glioma

Published on: November 11, 2021

Giovannoni et al. reply.

Stephen Giovannoni1, Ben Temperton, Yanlin Zhao

  • 1Department of Microbiology, Oregon State University, Corvallis, Oregon 97331, USA.

Nature
|July 27, 2013
PubMed
Summary
This summary is machine-generated.

Bacterial abundance is determined by the balance between top-down and bottom-up control, with defense specialization playing a key role in bacterial survival against predation. This highlights the importance of resource allocation for defense in microbial ecology.

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Area of Science:

  • Microbial Ecology
  • Evolutionary Biology

Background:

  • The regulation of bacterial populations is debated, with models proposing either top-down (predation) or bottom-up (resource availability) control.
  • Defense mechanisms are crucial for bacteria due to the high prevalence of viral predators.

Purpose of the Study:

  • To address the debate on top-down versus bottom-up control in bacterial populations.
  • To clarify the concept of 'defense specialism' in bacteria and its role in population dynamics.

Main Methods:

  • This study is a response to a previous communication, involving theoretical discussion and interpretation of ecological principles.
  • Analysis of the interplay between predation, resource competition, and bacterial defense strategies.

Main Results:

  • Bacterial abundance is likely determined by an equilibrium between top-down and bottom-up processes, especially when transport rates are low.
  • Defense specialism, where bacteria allocate significant resources to defense, can lead to ecological success.

Conclusions:

  • Both top-down and bottom-up controls are important for bacterial populations.
  • Defense specialism is a distinct strategy from general defense, crucial for bacterial survival and success in predator-rich environments.