Name: population size, density, and community roles
Uploaded: 2026-06-01T06:28:04.090Z
Duration: 30 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

North Carolina K-12 Science Standard Course of Study

9-12

Biology

ecosystems-interactions-energy-and-dynamics

Ecosystems- Interactions, Energy, and Dynamics

LS.Bio.4.2

What are Populations and Communities?

- [Narratore] Una popolazione
è formata da più individui

della stessa specie che
vivono uno stesso habitat,

come queste lepri nel deserto.

Più popolazioni di specie
diverse che interagiscono

e condividono uno stesso
habitat, formano una comunità.

Ad esempio, i coyote si
nutrono di lepri, e le

lucertole usano le tane
delle lepri nei giorni caldi.

Lo studio dell'interazione
di questi organismi

con l'ambiente e tra di
loro, si chiama ecologia.

Pyron, Mark. "Caratterizzare le comunità". Conoscenza dell'educazione alla natura 3 n. 10 (2010): 39. [<a href="https://www.nature.com/scitable/knowledge/library/characterizing-communities-13241173" target="__blank">Sorgente</a>]

Griffin, John N. "Ripartizione delle risorse e perché è importante". Conoscenza dell'educazione alla natura 3, n. 10 (2011): 49. [<a href="https://www.nature.com/scitable/knowledge/library/resource-partitioning-and-why-it-matters-17362658" target="__blank">Sorgente</a>]

Lang, Jennifer M. e M. Eric Benbow. "Interazioni tra specie e competizione". Conoscenza dell'educazione alla natura 4, n. 4 (2013): 8. [<a href="https://www.nature.com/scitable/knowledge/library/species-interactions-and-competition-102131429" target="__blank">Sorgente</a>]

cosa sono le popolazioni e le comunità?

<h4>Panoramica</h4>

Le popolazioni sono gruppi di individui della stessa specie che abitano un ambiente condiviso. Le comunità includono più popolazioni coesistenti e interagenti di specie diverse. Le metapopolazioni si estendono su più popolazioni della stessa specie che occupano aree diverse. Le metapopolazioni interagiscono attraverso l'immigrazione e l'emigrazione, fornendo una diversità genetica che conferisce resilienza ad ambienti difficili. Le dimensioni e la densità della popolazione possono essere stimate utilizzando i metodi di quadrata e marcatura e riacquisizione.

<h4>Le popolazioni sono dinamiche e interattive</h4>

Una popolazione, o gruppo di individui, appartenente alla stessa specie e che abita la stessa area generale, cambia continuamente in risposta a fattori biotici (viventi) e abiotici (non viventi). Fattori abiotici influenti includono il tempo, l'elevazione, la latitudine, la composizione del suolo e dell'acqua, e l'inquinamento, tra gli altri. Lo studio biologico di come gli organismi interagiscono tra loro e il loro ambiente è chiamato ecologia.

Le metapopolazioni includono più popolazioni della stessa specie che abitano aree distinte. Le metapopolazioni si scambiano continuamente i membri attraverso l'immigrazione, il movimento in un'area e l'emigrazione, il movimento da un'area. Questo scambio garantisce la diversità genetica, aiutando le popolazioni a resistere a condizioni ambientali imprevedibili e sfavorevoli aumentando la probabilità che i tratti adattativi (cioè utili) siano selezionati naturalmente (cioè emergono nella popolazione).

<h4>Le comunità sono combinazioni di popolazioni co-esistenti e interagenti</h4>

Una comunità ecologica è composta da più popolazioni che coesistono e interagiscono nello stesso habitat, e la ricchezza delle specie di una comunità è semplicemente il numero di specie. La combinazione di modi in cui una specie utilizza le risorse ambientali e interagisce con gli altri membri della comunità riflette la nicchia distinta che la specie occupa. In altre parole, una nicchia è come il "lavoro" che una specie svolge nella sua comunità.

La competizione si verifica quando le nicchie delle specie si sovrappongono. Bluebirds e picchi prediligono entrambi diete insettivore e aree aperte con alberi scarsamente distribuiti. In un iesempio di concorrenza interspecifica, queste due specie si contendono risorse alimentari e abitative limitate. I Bluebirds competono anche con altri uccelli blu per queste risorse (concorrenza intraspecifica). La concorrenza può essere evitata partizionando le risorse o occupando diverse aree di un ambiente condiviso.

Le relazioni predatore-preda, un'altra importante interazione della comunità, assomigliano a una "corsa agli armamenti" evolutiva. Negli animali preda, la selezione naturale favorisce fortemente le caratteristiche che aiutano a prevenire la predazione. Ad esempio, le farfalle Caligo (o "Gufo") hanno grandi occhi sulle ali che assomigliano agli occhi di gufo, che scoraggiano i predatori minacciosi. I predatori co-adattano anche agli adattamenti delle prede; sia le specie predatori che prede (ad esempio, dei cervi) usano il camuffamento per evitare il rilevamento.

<h4>Le popolazioni possono essere misurate utilizzando i metodi Quadrat e Mark (marcatura) e Recapture (riconquista) </h4>

Le popolazioni sono caratterizzate da dimensioni e densità. La dimensione della popolazione (N) è semplicemente il numero di individui. La densità di popolazione si riferisce al numero di individui in una determinata area. Anche se il conteggio degli individui è il modo più accurato per misurare le popolazioni, può essere irrealizzabile nei grandi habitat o negli organismi che si muovono frequentemente. Pertanto, i ricercatori spesso utilizzano metodi di campionamento per dedurre la dimensione totale della popolazione.

I campioni di Quadrat sono adeguati per stimare le dimensioni della popolazione e la densità delle piante o di organismi molto piccoli o lenti. Questo metodo prevede il partizionamento di diverse sezioni di habitat distribuite casualmente con marcatori, come stringa o pali, e il conteggio degli individui in ogni quadrante. Il numero e le dimensioni dei quadranti necessari per stime accurate variano a seconda delle specie. Ad esempio, gli organismi più piccoli, come i batteri, richiedono aree di campionamento molto più piccole rispetto agli organismi di grandi dimensioni, come gli alberi.

I metodi di marcatura e riconquista sono più adatti per lo spostamento di animali, come mammiferi, pesci e uccelli. In primo luogo, un campione casuale di individui provenienti da un habitat vengono catturati, contrassegnati (ad esempio, con tag, vernici o bande) e ripubblicati. In un secondo momento, viene catturato un secondo campione casuale, che include alcuni degli animali contrassegnati dal primo campione. Il rapporto tra animali contrassegnati e animali non marcati viene quindi utilizzato per stimare le dimensioni della popolazione. Le limitazioni di questo metodo includono presupposti che gli animali catturati in precedenza e non catturati hanno ugualmente probabilità di essere catturati nel secondo campione, e nessun animale è morto, è nato o si è spostato tra i punti temporali.

Cosa sono le popolazioni e le comunità?

Panoramica

Le popolazioni sono gruppi di individui della stessa specie che abitano un ambiente condiviso. Le comunità includono più coesistenti, ...

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Education

Didattica

JoVE Core

Biologia

Ecology

Ecologia

Population and Community Ecology

Ecologia delle popolazioni e delle comunità

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

population size, density, and community roles

Populations, metapopulations, and communities are key parts of ecology. Ecology is the study of how organisms interact with each other and with their environment. A population is a group of individuals of the same species that live in the same general area. A community includes multiple populations of different species that coexist and interact in one habitat.

Populations are dynamic because they respond to biotic and abiotic factors. Biotic factors are living influences, and abiotic factors are non-living influences. Weather, elevation, latitude, soil and water composition, and pollution can all affect population change. Metapopulations are multiple populations of the same species that live in separate areas. They stay connected through immigration, which is movement into an area, and emigration, which is movement out. This exchange helps maintain genetic diversity and can make populations more resilient in harsh or unpredictable conditions.

Communities are more than just a list of species. Species richness is the number of species in a community. Each species also has a niche, which is the set of resources it uses and the role it plays in the community. When niches overlap, competition can happen. Bluebirds and woodpeckers are an example. Both may feed on insects and use open areas with scattered trees, so they compete for food and housing. Bluebirds also compete with other bluebirds. That is intraspecific competition. Competition between different species is interspecific competition. Species can reduce competition by partitioning resources, or by using different parts of the same environment.

Predator-prey relationships are another major community interaction. They can act like an evolutionary arms race. Prey traits that help avoid predation are favored by natural selection. Caligo, or owl, butterflies have large eyespots on their wings that look like owl eyes and can scare predators away. Predators can also adapt in response to prey. Camouflage is one example seen in both predators, such as leopards, and prey, such as deer.

Scientists estimate population size and density in different ways. Population size is the number of individuals, and population density is the number of individuals in a given area. Counting every organism is the most accurate method, but it is not always practical in large habitats or for animals that move often. Quadrat sampling works well for plants and for very small or slow organisms. Researchers place random sample areas in a habitat and count the individuals inside each quadrat. The number and size of quadrats depend on the species. Smaller organisms, such as bacteria, need smaller sampling areas than larger organisms, such as trees.

Mark and recapture is better for moving animals like mammals, fish, and birds. First, researchers capture a random sample, mark the individuals with tags, paint, or bands, and release them. Later, they capture a second sample and count how many marked individuals appear again. The ratio of marked to unmarked animals is used to estimate population size. This method depends on several assumptions. It assumes marked and unmarked animals are equally likely to be caught the second time. It also assumes no animals died, were born, or moved between samples.

Population Size, Density, and Community Roles

population-size-density-and-community-roles

what are populations and communities?

Populations, metapopulations, and communities are key parts of ecology. Ecology is the study of how organisms interact with each other and with their environment. A population is a group of individuals of the same species that live in the same general area. A community includes multiple populations of different species that coexist and interact in one habitat. Populations are dynamic because they respond to biotic and abiotic factors. Biotic factors are living influences, and abiotic factors...

distribution and dispersion

Species Range and Spacing Patterns

Ecology looks at how organisms interact with each other and with their environment. It also examines where species live and how individuals are arranged within those areas. The geographic range of a species is the total area where its members are found. Dispersion is the pattern of spacing among individuals inside that range. Within a species’ geographic range, dispersion can follow three main patterns: uniform, random, or clumped. These patterns depend on environmental conditions and on...

life histories

Life History Strategies and Survivorship

Life history strategies show how organisms balance survival and reproduction across a lifetime. An organism’s life history includes birth, growth, sexual maturation, reproduction, and death. These patterns reflect trade-offs in how much energy and resources go to making offspring and caring for them. R-strategists and K-strategists show two common reproductive strategies. R-strategists, with r standing for rate, have high fecundity, or reproductive potential. They produce many offspring that...

energy budgets and reproductive strategies

Reproductive Trade-Offs in Life Cycles

Organisms must divide limited energy between growth, maintenance, and reproduction. These energy budgets create trade-offs. Energy used for reproduction cannot be used for survival or growth, so species follow different reproductive patterns. Semelparity and iteroparity are two main strategies on this continuum. Semelparous species reproduce only once in their lifetime. They usually put most or all available resources into that single reproductive event and then die. This approach often...

population growth

Population Growth Curves and Carrying Capacity

Population growth changes with births, deaths, immigration, and emigration. When birth rates and immigration are higher than death rates and emigration, a population increases. When deaths and emigration are higher, the population decreases. These changes can be shown on a graph of population size over time. Under ideal conditions with unlimited resources, populations can grow exponentially. This produces a J-shaped growth curve. Such rapid growth is seen in newly introduced invasive species...

ecological niches

How Species Share Ecological Niches

Ecological niches describe how species fit into an ecosystem. A niche includes the living and nonliving factors that shape where an organism can live. Food resources, climate, and terrain are all part of that role. Two species cannot occupy the exact same niche in the same habitat for long. When their niches overlap too much, the competitive exclusion principle applies. One species will outcompete the other, and the weaker species must adapt or disappear. Similar species can still coexist...

symbiosis

Symbiosis and Species Interactions

Symbiosis and other close species interactions shape how organisms live together in a community. These long-term relationships can affect the distribution and abundance of the species involved. They also often lead to co-evolution, where species change in response to one another. Mutualism is a symbiotic relationship that benefits both species. A common example is ants and aphids. Aphids feed on phloem in plant stems with piercing mouthparts and release a sugary fluid. Ants feed on this fluid,...

competition

How Limited Resources Shape Competition

Competition happens when organisms need the same limited resources in an environment. It is a net-negative interaction because both competitors lose fitness when neither has full access to the resource. This can happen even without direct contact between the competing individuals or populations. Competition within a species is called intraspecific competition. It often helps control population size because rapid growth can lead to crowding and fewer available resources. Stronger individuals...

predator-prey interactions

Predator and Prey Evolution

Predator and prey evolution shapes how animals survive and reproduce. Predators gain energy by eating prey, while prey that avoid being eaten improve their fitness. Over time, both sides develop traits that help them win this struggle. Predators often evolve tools for attack, such as claws, teeth, and speed. Prey evolve defenses that help them escape or stay hidden. These defenses can include crypsis, or blending in with the background, aposematism, or warning coloration, and mimicry, which is...

keystone species

Sea Stars, Wolves, and Ecosystem Balance

Keystone species help keep ecosystems balanced. In ecology, biodiversity is often described by species richness, which is the number of species present, and evenness, which is how evenly those species are represented. Community structure can also be shaped by abiotic factors such as sunlight and nutrients, disturbances such as fire or flood, species interactions such as predation or competition, and chance events such as the invasion of a foreign species. A keystone species has a much larger...

ecological disturbance

Disturbance Patterns and Biodiversity

Ecological disturbance is a temporary disruption in an environment that can change an ecosystem in a major way. It may come from abiotic, biotic, or human-caused factors. The size of the impact depends on the disturbance’s intensity, how often it happens, and how widely it spreads. Disturbances can be very small or very large. Trampling underbrush is one example of a small disturbance. Forest fires and floods are larger examples. Natural events such as volcanoes and hurricanes can also disturb...

ecological succession

How Succession Shapes Ecosystem Recovery

Ecological succession is shaped by facilitation, inhibition, and toleration. These processes explain how one community changes into the next after a disturbance or a new surface becomes available. Early species can either help, block, or simply coexist with later species. Facilitation happens when pioneer species make conditions better for later species. They may increase nutrients, water, or light. In inhibition, early species make conditions worse by limiting resources. In some cases, later...

key terms and concepts

Explore how populations, metapopulations, and communities differ, plus how scientists estimate population size with quadrats and mark and recapture methods.

Population Size, Density, and Community Roles | JoVE K12

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Pennsylvania State Academic Standards

Life Science

interdependent-relationships-in-ecosystems

Interdependent Relationships in Ecosystems

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Life Sciences

Ecosystems: Interactions, Energy And Dynamics

HS-LS2-6

Environmental Science

HS-LS2-1

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Ohio’s Learning Standards and Model Curriculum

Diversity And Interdependence Of Life

Ecosystems

Loss of diversity

Tennessee Academic Standards

Ecosystems: Interactions, Energy, and Dynamics

BIO1.LS2.1

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BIO.7

BIO.7.b

BIO.8

BIO.8.a

LS.6

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Minnesota Academic Standards in Science

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9L.2.1.1.2

3.2.1 9L.3.2.1.4

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New Jersey Student Learning Standards for Science

Alabama Course of Study Science

Ecosystems: Interactions Energy and Dynamics

9-12.B.2.6

Unity and Diversity

9-12.EVS.2.3

Earth and Human Activity

9-12.EVS.4.11.a

Next Generation Science Standards

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Florida Department of Education

SC.912.L.17

SC.912.L.17.1

SC.912.L.17.5

SC.912.L.17.18

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South Carolina College and Career Ready Science Standards

B-LS2-2.

B-LS2-4.

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New York State Science Learning Standards

HS-LS2-2.

Georgia Standards of Excellence

SEC1.

SEC1.a

SB5.a

What are Biogeochemical Cycles?

The most common elements in organic molecules, carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus, are only available in the ecosystem in limited ...

The Water Cycle

The Earth&rsquo;s hydrosphere includes all of the areas where the storage and movement of water occurs. Since water is the basis of all living processes, ...

The Carbon Cycle

Carbon is the basis of all organic matter on Earth, and is recycled through the ecosystem in two primary processes: one in which carbon is exchanged among ...

The Nitrogen Cycle

Nitrogen atoms, present in all proteins and DNA, are recycled between abiotic and biotic components of the ecosystem. However, the primary form of ...

The Phosphorus Cycle

Unlike carbon, water, and nitrogen, phosphorus is not present in the atmosphere as a gas. Instead, most phosphorus in the ecosystem exists as compounds, ...

The Sulfur Cycle

Sulfur, an important element in the chemical makeup of proteins, is recycled through the atmosphere and aquatic and terrestrial environments. Found in the ...

Use models to illustrate how processes in organisms contribute to the flow of energy and the cycling of matter within an ecosystem.

LS.Bio.4.1

Populations are groups of individuals of the same species that inhabit a shared environment. Communities include multiple co-existing, interacting ...

Distribution and Dispersion

Ecology is the study of how organisms interact with their environment and with one another. An important aspect of ecology is understanding where species ...

Life Histories

Constrained by limited energy and resources, organisms must compromise between offspring quantity and parental investment. This trade-off is represented ...

Energy Budgets and Reproductive Strategies

Organisms must balance energy intake with the energy required for growth, maintenance, and reproduction. These trade-offs result in a variety of ...

Population Growth

Population size is dynamic, increasing with birth rates and immigration, and decreasing with death rates and emigration. In ideal conditions with ...

Use models to explain the relationship between the flow of energy and cycling of matter among organisms in an ecosystem.

Ecological Niches

All organisms have a position within an ecosystem. The complete set of living and nonliving factors&#x2014;including food resources, climate, and ...

Ecological Succession

Ecological succession is influenced by the processes of facilitation, inhibition, and toleration. Facilitation occurs when early successional species ...

Keystone Species

Measures of species biodiversity, such as richness (i.e., the number of species present) and evenness (i.e., their relative abundance), describe an ...

Symbiosis

Symbiotic relationships are long-term, close interactions between individuals of different species that affect the distribution and abundance of those ...

Competition

When organisms require the same limited resources within an environment, they may have to compete for them. Competition is a net-negative interaction. ...

Predator-Prey Interactions

Predators consume prey for energy. Predators that acquire prey and prey that avoid predation both increase their chances of survival and reproduction ...

Ecological Disturbance

An ecological disturbance is a temporary disruption in the environment resulting from abiotic, biotic, or anthropogenic factors, causing a pronounced ...

Use mathematics and computational thinking to explain how interactions between organisms (predator/prey, competition) affect carrying capacity and maintain stability in an ecosystem.

LS.Bio.5.1

What is Biodiversity?

Biodiversity describes the variety of living things at multiple organizational levels: genetic, species and ecosystem diversity. Species diversity ...

Threats to Biodiversity

There have been five major extinction events throughout geological history, resulting in the elimination of biodiversity, followed by a rebound of species ...

Biodiversity and Human Values

Human civilization relies on biodiversity in many ways. Sudden changes in species biodiversity result in environmental changes that can modify weather ...

What is Conservation Biology?

Conservation biology is a scientific field that focuses on the preservation of biodiversity in order to protect ecosystems while meeting the needs of the ...

Sustainable Development

As the human population continues to grow and use resources, we must be mindful of our planet&rsquo;s natural limits. Sustainable development provides a ...

Conservation of Small Populations

Small population sizes put a species at extreme risk of extinction due to a lack of variation, and a consequent decrease in adaptability. This weakens ...

What is Weather?

Overview

Weather refers to the current state of atmospheric conditions at a specific time and place. Weather is temporary and is influenced by the ...

Global Climate Change

Throughout its ~4.5 billion year history, the Earth has experienced periods of warming and cooling. However, the current drastic increase in global ...

Conservation of Declining Populations

Conservation of declining population focuses on ways of detecting, diagnosing, and halting a population decline. The approach uses methods to prevent ...

Habitat Fragmentation

Habitat fragmentation describes the division of a more extensive, continuous habitat into smaller, discontinuous areas. Human activities such as land ...

Engage in argument from evidence to evaluate various solutions to reduce the impact of human activities on biodiversity and ecosystem health.

LS.Bio.5.2

Analyze the relationships between matter and energy within ecosystems.

Population Size, Density, and Community Roles

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