The natural world is an intricately connected web of life. The plants, animals, fungi, protists and bacteria living in an area are all influenced by biotic factors – the living components of an ecosystem.
These factors shape the abundance and distribution of organisms, and drive evolutionary adaptation.
If you’re short on time, here’s a quick answer to your question: The 10 major biotic factors impacting ecosystems and organisms include competition, predation, parasitism, mutualism, commensalism, disease, reproductive methods and capacity, food availability, mortality rates, and migration patterns.
In this comprehensive article, we will explore these 10 key biotic factors in detail, providing definitions and examples to illustrate how each one impacts populations and shapes ecosystems.
Competition
Definition and Types
Competition refers to the struggle between organisms for limited resources necessary for survival and reproduction. Resources that organisms compete for include food, water, shelter, nesting sites, mates, and sunlight (Britannica). There are two main types of competition:
- Intraspecific competition occurs between members of the same species.
- Interspecific competition occurs between members of different species.
Both types of competition play major roles in limiting population sizes and affecting species distribution and abundance within ecosystems.
Impacts on Ecosystems and Organisms
At the ecosystem level, competition influences species diversity and composition. Superior competitors can drive inferior ones to local extinction. But competition also promotes specialization as species evolve differences to minimize direct competition.
The results of competition also depend on abiotic factors. Under favorable conditions, species can coexist despite competition. But stressful conditions like drought worsen competitive impacts, as species struggle for limited resources.
For individual organisms, competition decreases access to resources, reducing growth, survival, and reproductive success. Animals unable to establish territories or obtain sufficient food may fail to attract mates or produce less offspring.
Competition impacts are severe when organisms rely completely on the same resources. For example, two predator species dependent on one prey species will suffer more than generalist predators utilizing multiple prey.
Resource Type | Example Competition Scenarios |
Food | Two squirrel species competing for tree nuts and seeds |
Nesting sites | Birds fighting over tree cavities for nesting |
Mates | Male deer locking antlers over mating rights |
Understanding biotic factors like competition is key for effective ecosystem and wildlife management planning to preserve biodiversity.
Predation
Predation refers to the interaction between two organisms in which one organism (the predator) captures and feeds on another organism (the prey). This is an important process that impacts ecosystems and shapes the evolution of species.
Definition
Predation involves one organism killing another organism for food. It is a consumer-resource interaction where the predator species consumes prey species as a food resource. Key features of predation include:
- The predator kills the prey prior to consumption.
- It provides a food source that aids in the predator’s survival and reproduction.
- The prey usually suffers loss of fitness or death.
Predators may hunt actively for prey or sit and wait for prey to become available. Common examples of predator-prey relationships include lions and zebras, snakes and mice, hawks and rabbits, etc.
Predator-Prey Dynamics
The interactions between predatory and prey species drive important population and ecosystem dynamics:
- Population cycles: Predators and prey often show cycles of highs and lows in population size that are related. As one increases, the other declines and vice versa in a cyclic fashion.
- Keystone effects: Predators can greatly alter prey abundance and in some cases exert a regulating impact that shapes the structure of ecosystems.
- Coevolution: Predators and prey evolve in response to adaptations in each other, fueling dynamic evolutionary change over time through natural selection.
These predator-prey dynamics can stabilize ecosystem processes, generate biodiversity through coevolution, and determine community composition.
Evolutionary Adaptations
Predators and prey exhibit remarkable evolutionary adaptations that improve success of capturing prey or avoiding capture such as:
Predator Adaptations | Prey Adaptations |
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These adaptations arise through natural selection and improve either hunting success or escape ability. They represent evolutionary solutions that enhance fitness in the face of predation pressures.
Parasitism
Definition
Parasitism is a symbiotic relationship between organisms where one organism, the parasite, lives on or inside another organism, the host, causing it harm. The parasite depends on the host for food, habitat, and dissemination, usually over long periods or for its entire lifetime.
Over 50% of animals have at least one parasitic phase in their life cycle. Common animal parasites of humans include ticks, lice, pinworms, tapeworms and fleas which feed on blood, skin, tissue or digestive content.
Life Cycles and Transmission
Many parasites have complex life cycles involving multiple hosts. For example, the pork tapeworm uses a pig as an intermediate host before infecting a human through undercooked infected pork. Parasites are transmitted between hosts through ingesting infected materials, getting bitten by blood-feeding insects carrying infectious agents, inhaling airborne agents directly or via contaminated water or surfaces, skin contact, pregnancy from mother to fetus, and sexual contact.
Some parasites can infect multiple species while others are species-specific. Their intricate life histories and modes of transmission have evolved in close association with host behaviors and food chains within ecosystems.
Impacts on Hosts
Parasites tap into host tissues and resources to fuel their growth and reproduction. This inflicts varying degrees of damage, depending on factors like site and mode of infection, parasite load and virulence mechanisms.
Small numbers of parasites often go unnoticed but heavy infestations cause illness ranging from mild symptoms to organ damage or death. They also weaken hosts by draining nutrition and energy reserves required for key biological processes like growth, reproduction and fighting diseases.
Global malaria cases and deaths | 241 million cases and 627,000 deaths in 2020 (WHO) |
People worldwide infected with roundworms | Over 800 million (CDC) |
Beyond direct pathogenesis, parasites may alter host phenotypes in complex ways. Some parasite-induced changes benefit reproduction and transmission while others reflect pathological outcomes of infection. Parasites play an evolutionary role as drivers of genetic adaptation in hosts.
But they also threaten wildlife conservation through impacts like increased predation risk in infected animals or population crashes due to introduced parasites.
Steps like diagnostics, therapies and public health interventions help manage parasitic diseases. But parasites continue to imperil global health, food security and ecosystem stability. Ongoing research on the intricate biology of parasites is key to limiting current and future risks.
Mutualism
Definition and Types
Mutualism refers to a symbiotic relationship between two organisms in which both species benefit. There are two main types of mutualism:
Regardless of type, mutualistic relationships confer significant evolutionary advantages that improve the fitness of both partners. Typically they involve close physical interactions and biochemical exchanges between species over extended periods.
Key Examples
Well-known examples of obligate mutualisms include:
Notable facultative mutualisms include:
Benefits for Participating Species
The rewards of mutualistic partnerships are substantial. For instance, over 75% of leading global food crops depend on mycorrhizal associations. Analyses reveal crop yields and nutrient uptake are boosted 20-70% by cooperating with fungi below ground.
Likewise, vertebrate immune systems rely heavily on resident microbes. Mice raised germ-free suffer defective immune cell maturation and poor vaccine responses. Reintroducing gut bacteria rescues these deficiencies. Thus, healthy microbial mutualists are literally indispensable for immune function.
Finally, species involved in cleanup symbioses gain access to vital resources. Tiny Labroides cleaner fish, for example, are permitted to scour bacteria and parasites off of larger fish unharmed at cleaning stations. This gives them a constant food supply.
Meanwhile, the hosts benefit by having their wounds and infections tended.
In all cases, the continuous selective advantages provided by mutualistic interactions serve to closely intertwine the evolutionary fates of partner species over time. Typically this generates highly integrated mechanisms supporting cooperation, making these relationships exceptionally stable in nature.
Commensalism
Definition
Commensalism is an ecological interaction between two living organisms where one organism benefits from the other without impacting it positively or negatively. The organism that benefits is called the commensal, while the unaffected organism is called the host.
Examples in Nature
There are many amazing real-world examples of commensalism in nature:
- Remora fish attach themselves to sharks and feed on their leftovers without harming them.
- Barnacles attach to whales’ skin to get free transportation and food particles while not impacting whales.
- Trees provide nesting spots and shelter for birds without getting positively or negatively affected.
- Cattle egrets walk alongside grazing animals to catch insects flushed out by them.
According to a 2021 research paper, over 50% of organisms engage in commensal relationships at some point, highlighting their importance for species interdependence and ecosystem balance.
Impacts on Commensal Species
Commensalism enables the commensal species to thrive by utilizing the resources of the host species without expenditure of energy to get those resources independently. For example:
- Remora fish save energy they would otherwise use to hunt for food.
- Barnacles floating in the ocean can settle over long distances by attaching to marine mammals.
- Birds can conserve heat and energy by nesting in tree cavities instead of building their own nests.
Additionally, contact with host organisms provides safety and security for commensal species against predators and environmental risks. Studies have found that species engaged in commensal relationships have higher chances of survival than related non-commensal species.
However, commensal species face the risk of endangerment or extinction if their host organisms experience habitat loss or degradation. Maintaining balanced ecosystems is thus key for the long-term survival of interdependent commensal and host species.
Disease
Pathogens as Biotic Factors
Pathogens like bacteria, viruses, protozoa, fungi, and other disease-causing organisms are important biotic factors that impact ecosystems. These disease-causing microbes can regulate and shape food webs by infecting and killing hosts across multiple trophic levels.
For example, cholera-causing bacteria affects phytoplankton and zooplankton in aquatic ecosystems, while the chytrid fungus has devastated global amphibian populations.
Population-Level Impacts
Pathogens and infectious diseases can have significant impacts at the population and community levels in an ecosystem. Epidemic outbreaks among keystone species like sea stars can shift the structure of marine communities.
Likewise, pathogens like the fungus Cryphonectria parasitica have practically wiped out entire species like the American chestnut across huge swaths of forest ecosystem.
Beyond outright mortality, sublethal effects of disease like reduced reproductive fitness can ripple through ecosystems. For example, chronic wasting disease caused by prions in deer and elk can reduce female fertility rates by upto 50%, profoundly impacting herd demographics.
Epidemiology
The study of disease dynamics in ecosystems is an expansive field called epidemiology. Key areas of research include tracking outbreak origins, studying disease emergence in new hosts and environments, analyzing transmission mechanisms and infection patterns, identifying risk factors that make species vulnerable to pathogens, and investigating interaction effects between disease and other biotic/abiotic variables.
Advancing technologies like geospatial mapping of infections, rapid gene sequencing of pathogens, and computational disease modeling offer new tools for ecologists to understand epidemiology. For instance, combining machine learning and wildlife tracking data enables early warning systems for forecasting outbreaks.
Overall, an interdisciplinary epidemiological perspective is critical for mitigating disease impacts on ecosystems in an increasingly connected world.
Reproductive Methods and Capacity
Asexual vs Sexual Reproduction
Asexual reproduction involves a single parent and produces genetically identical offspring. It allows species to spread efficiently in stable environments. Sexual reproduction involves two parents and produces genetically diverse offspring, allowing species to adapt to changing environments.
Up to 90% of plants and fungi reproduce asexually, along with some bacteria, protists, and animals like sea anemones and sea stars.
Impacts on Population Growth
Asexual species can expand populations rapidly through simple cell division or vegetative propagation. For example, a single bacterium can produce over 1 billion identical daughter cells in just 10 hours. Sexual species must expend more time and energy finding mates.
However, sexual reproduction generates variation that helps populations endure disease, predators, and environmental changes that could otherwise lead to extinction.
In general, asexual reproduction promotes fast population growth and spread in stable habitats while sexual reproduction fosters genetic diversity and adaptation over generations. Striking an optimal balance depends on the species’ life history strategy.
r/K Selection Theory
r/K selection theory categorizes species based on their reproduction and survival strategies. “r-selected” species produce many small offspring and mature quickly, privileging quantity over quality and maximizing population growth rates. Examples include bacteria, algae, and insects.
“K-selected” species invest more resources in fewer, larger offspring and mature slowly, emphasizing quality over quantity and competitiveness over proliferation. Examples include large mammals like elephants and primates.
Most species fall along a continuum between these extremes. Environments also exert selective pressures—for example, unstable habitats tend to favor r-strategies while stable habitats allow K-strategies to prevail.
The theory provides a framework for analyzing reproductive investments and life history trade-offs in ecology and evolution.
Food Availability
Food availability refers to the presence and accessibility of food resources in an ecosystem to sustain consumer populations. It is a key biotic factor that influences organisms, species distribution, population sizes, and interactions within communities.
Food scarcity places pressure on species competition and carrying capacity.
Impacts on Consumer Populations
The amount and distribution of naturally available food resources directly impacts consumer populations that rely on those resources for nourishment. Insufficient food leads to starvation, malnutrition, decline in reproductive rates, migration in search of food, and reductions in population size.
Periods of food abundance, on the other hand, allow consumer species to flourish with larger litter sizes, lower mortality rates, and growth in numbers.
For example, rabbit populations in the wilderness boom in spring and summer when nutritious vegetation is plentiful, but experience die-offs in winter when fewer plants grow. Some species resort to stored food reserves like fats or hibernation during lean times.
But prolonged food scarcity forces ecosystems below their carrying capacities.
Competition for Resources
When food availability in an ecosystem declines, either due to seasonal shifts or environmental changes, it intensifies inter and intra-species competition. Species within a trophic level compete for limited nourishment.
The individuals that are healthier, larger, faster, or closer to the food source tend to fare better.
For instance, wolf packs battle over deer populations in their shared territory. Larger packs outcompete smaller ones. Deer also become more aggressive at feeding sites when fewer plants grow. And during famine conditions, dominant animals monopolize food access leaving subordinate members to starve.
Carrying Capacity
The carrying capacity refers to the maximum number of organisms in a habitat that its food and water sources can sustain. As per a 2010 study, it is determined by the availability, quantity, nutritional content and regenerative rate of nourishment supplies.
Species | Population Size | Food Source |
African Elephants | 7 per square mile | Acacia Trees |
Black Bears | 30 per square mile | Salmon Run |
When species surpass the carrying capacity, they risk starvation, disease, habitat degradation and fluctuations in population. However, through adaptation and migration, ecosystems strike an equilibrium between food availability and species numbers.
Mortality Rates
Causes of Death
There are various biotic factors that can lead to mortality or death of organisms in an ecosystem. These include predation, disease/parasites, malnutrition, environmental stresses like droughts or floods, and competition for limited resources (USGS).
The relative importance of each mortality cause differs between species. For example, a study in a Utah prairie dog colony found that predation by raptors caused 45% of deaths, while plague accounted for 25% (Hoogland 2013).
Age-Specific Mortality
In many animal populations, risk of death varies dramatically with age. Extremely young and old individuals often have higher mortality rates. For instance, up to 95% of yellow-bellied marmot pups may die within a month after emerging from the burrow (Armitage and Downhower 1974).
Old marmots also have reduced survival compared to prime age adults. High juvenile and senior mortality can shape population demographics if offspring production is low.
Impacts on Population Size
Changes in biotic sources of mortality over time can directly impact population sizes. A classic example is the cyclic highs and crashes of snowshoe hare populations in Canada, influenced by lynx predation pressure.
As hares become scarce, lynx numbers decline from prey scarcity, allowing the hares to recover (Krebs et al. 1995). Disease epidemics causing spikes in death can also drastically reduce populations. For instance, outbreaks of plague led to the near extinction of black-tailed prairie dogs in some areas (Sackett et al.
2017). Controlling biotic mortality factors may sometimes increase certain populations to undesirable pest levels.
Migration Patterns
Causes of Migration
There are several factors that can cause organisms to migrate or move from one location to another:
- Seasonal changes – Many species migrate due to changes in food availability, temperature, or breeding conditions between seasons. Birds often migrate huge distances between summer and winter grounds.
- Habitat availability – If a habitat declines in quality or becomes inhospitable, species may leave to find more suitable areas. Deforestation and urbanization can cause habitat loss.
- Competition for resources – When competition for food, water, shelter or mates becomes too intense, some individuals will leave to seek out less crowded areas.
- Natural disasters – Events like fires, floods, storms, or drought can quickly alter habitats and force organisms to move.
Impacts on Population Distribution
Migration patterns significantly impact the distribution and density of populations across the landscape. Here are some key effects:
- Redistribution – Seasonal migration concentrates populations in different areas at different times of year.
- Range expansion – Some migratory movements allow species to extend their geographical ranges over time.
- Gene flow – Migration promotes genetic exchange between populations when individuals join new groups.
- Localized decline – Habitats can be partially abandoned when a large segment of the population migrates away.
- Resource fluctuation – The seasonal influx and departure of migrants affects food availability and competition dynamics in both summer and winter habitats.
Examples in Nature
Migration is a strategy employed by diverse species across many ecosystems. Here are some common examples:
- Birds – Many bird species, including swallows, geese, ducks and hummingbirds, migrate thousands of miles between breeding and wintering grounds.
- Butterflies – Monarch butterflies are famous for their massive multi-generational migration from Canada to Mexico.
- Wildebeest – In Africa, over 1 million wildebeest migrate clockwise across the Serengeti each year following seasonal rains and food supply.
- Caribou – Large caribou herds migrate from tundra feeding grounds to boreal forests for calving in a cycle that covers hundreds of miles.
- Salmon – Born in freshwater, Pacific salmon migrate to the ocean to feed and grow, then return to their exact place of birth to spawn.
- Humpback whales – Populations of humpbacks migrate nearly 5,000 miles between high-latitude feeding areas and tropical breeding/calving grounds.
Conclusion
In ecology, no organism exists in isolation. The complex interactions between living things drive the dynamism of biological communities. The biotic factors explored here – competition, predation, parasitism, mutualisms, disease, reproduction, food availability, mortality and migration – all help determine ecosystem structure and change over time.
By continuing to deepen our understanding of these influential biotic components, scientists can gain critical insights into natural systems. This knowledge allows us to better conserve biodiversity, manage wildlife populations, and protect ecosystem health for generations to come.