Chapter 5 Outline

5.1 Interactions of Populations – Predation and Herbivory

5.2 Symbiosis – Close Interactions between Species

5.3 Competition and the Competitive Exclusion Principle

5.4 Characteristics and Components of Communities

5.5 Community Dynamics

Learning Outcomes

After studying this chapter, each student should be able to:

• 5.1 Describe how predator and prey populations interact, and various ways the prey species avoid predation
• 5.2 Describe different forms of symbioses, such as commensalism, mutualism, and parasitism
• 5.3 Differentiate between intraspecific and interspecific competition, and explain how the competitive exclusion theory explores ways that potentially competing species may partition resources
• 5.4 Describe the different components of a community, such as foundation, keystone, and invasive species, and how community biodiversity varies across the earth
• 5.5 Understand the concept of change and succession in a community, and differentiate between primary and secondary succession

5.1 Interactions of Populations – Predation and Herbivory

Introduction

Populations rarely, if ever, live in isolation from populations of other species. In most cases, numerous species share a habitat. The interactions between these populations play a major role in regulating population growth and abundance. All populations occupying the same habitat form a community: populations inhabiting a specific area at the same time. The number of species occupying the same habitat and their relative abundance is known as species diversity. Areas with low diversity, such as the glaciers of Antarctica, still contain a wide variety of living things, whereas the diversity of tropical rainforests is so great that it cannot be counted. Ecology is studied at the community level to understand how species interact with each other and compete for the same resources.

Predation and Herbivory

Perhaps the classic example of species interaction is the predator-prey relationship. During predation, individuals of one population kill and then consume the individuals of another population. Predators are the organisms killing and eating the other organisms.  Prey are the organisms being killed and consumed by the predators. Population sizes of predators and prey in a community are not constant over time, and they may vary in cycles that appear to be related. One example of predator-prey population dynamics is seen in the cycling of the lynx (predator) and the snowshoe hare (prey), using 100 years of trapping data from North America (Figure 1). An apparent explanation for this pattern is that as the hare numbers increase, there is more food available for the lynx, allowing the lynx population to increase as well. When the lynx population grows to a threshold level, however, they kill so many hares that hare numbers begin to decline, followed by a decline in the lynx population because of scarcity of food. When the lynx population is low, the hare population size begins to increase due, in part, to low predation pressure, starting the cycle anew.

Figure 1. The cycling of lynx and snowshoe hare populations in Northern Ontario is an example of predator-prey dynamics. (Credit: “Predator-prey Dynamics” by OpenStax is licensed under CC BY 4.0)

Herbivory describes the consumption of plants by insects and other animals, and it is another interspecific relationship that affects populations. Unlike animals, most plants cannot outrun predators or use mimicry to hide from hungry animals. Some plants have developed mechanisms to defend against herbivory. Other species have developed mutualistic relationships; for example, herbivory provides a mechanism of seed distribution that aids in plant reproduction.

Predation and predator avoidance are strongly influenced by natural selection. Any heritable character that allows an individual of a prey population to better evade its predators will be represented in greater numbers in later generations. Likewise, traits that allow a predator to more efficiently locate and capture its prey will lead to a greater number of offspring and an increase in the commonness of the trait within the population. Such ecological relationships between specific populations lead to adaptations that are driven by reciprocal evolutionary responses in those populations. Species have evolved numerous mechanisms to escape predation (including herbivory, the consumption of plants for food). Defenses may be mechanical, chemical, physical, or behavioral.

 

Mechanical defenses, such as the presence of thorns in plants or armor in animals, discourage predation and herbivory by discouraging physical contact (Figures 2a,b&d). Chemical defenses, such as the production of defensive chemicals in the body tissue of plants or animals, makes these organisms unpalatable, noxious, or even toxic to potential predators. Many plant species produce secondary plant compounds that serve no function for the plant except that they are toxic to animals and discourage consumption. For example, the foxglove produces several compounds, including digitalis, that are extremely toxic when eaten (figures 2c & 2d). (Biomedical scientists have repurposed the chemical produced by foxglove as a heart medication, which has saved lives for many decades.)

Figure 2. The (a) honey locust tree (Gleditsia triacanthos) uses thorns, a mechanical defense, against herbivores, while the (b) Florida red-bellied turtle (Pseudemys nelsoni) uses its shell as a mechanical defense against predators. (c) Foxglove (Digitalis sp.) uses a chemical defense: toxins produced by the plant can cause nausea, vomiting, hallucinations, convulsions, or death when consumed. (d) The North American millipede (Narceus americanus) uses both mechanical and chemical defenses: when threatened, the millipede curls into a defensive ball and produces a noxious substance that irritates eyes and skin. (Credit: Attribution: a: modification of work by Huw Williams; credit b: modification of work by “JamieS93”/Flickr; credit c: modification of work by Philip Jӓgenstedt; credit d: modification of work by Cory Zanker accessed from OpenStax is licensed under CC BY 4.0)

Many species use their body shape and coloration as camouflage to avoid being detected by predators, a natural phenomenon called “cryptic coloration”. The tropical walking stick is an insect with the coloration and body shape of a twig, which makes it very hard to see when it is stationary against a background of real twigs (Figure 3a). In another example, the chameleon can change its color to match its surroundings (Figure 3b).

Figure 3. (a) The tropical walking stick and (b) chameleon use body shape and/or coloration to prevent detection by predators. (Credit: Attribution: a: modification of work by Linda Tanner; b: modification of work by Frank Vassen; accessed from OpenStax is licensed under CC BY 4.0)

Some species use warning coloration, a particular color or color pattern that warns predators that they are distasteful or poisonous. For example, the monarch butterfly caterpillar sequesters poisons from its food (especially milkweeds) to make itself poisonous or distasteful to potential predators. The caterpillar is bright yellow and black to advertise its toxicity. The caterpillar is also able to pass the sequestered toxins on to the adult monarch, which is also dramatically colored black and red as a warning to potential predators. Fire-bellied toads produce toxins that make them distasteful to their potential predators (Figure 4). They have bright red or orange coloration on their bellies, which they display to a potential predator to advertise their poisonous nature and discourage an attack. Warning coloration only works if a predator uses eyesight to locate prey and can learn—a naïve predator must experience the negative consequences of eating one before it will avoid other similarly colored individuals.

Figure 4. (a) The strawberry poison dart frog (Oophaga pumilio) uses aposematic coloration to warn predators that it is toxic, while the (b) striped skunk (Mephitis mephitis) uses aposematic coloration to warn predators of the unpleasant odor it produces. (Credit:  a. modification of work by Jay Iwasaki; b: modification of work by Dan Dzurisin accessed from OpenStax is licensed under CC BY 4.0)

While some predators learn to avoid eating certain potential prey because of their coloration, other species have evolved mechanisms to mimic this coloration to avoid being eaten, even though they themselves may not be unpleasant to eat or contain toxic chemicals. In some cases of mimicry, a harmless species imitates the warning coloration of a harmful species (called batesian mimicry). Assuming they share the same predators, this coloration then protects the harmless ones. Many insect species, such as the syrphid and robber flies, mimic the coloration of bees, which are stinging, venomous insects, thereby discouraging predation (figure 5).

Figure 5. Batesian mimicry occurs when a harmless species mimics the coloration of a harmful species, as is seen with the (a) bumblebee and (b) bee-like robber fly. (Credit: a&b: modification of work by Cory Zanker accessed from OpenStax is licensed under CC BY 4.0)

In other cases of mimicry, multiple species that are poisonous or share the same warning coloration (called mullerian mimicry), but all of them actually have defenses. The commonness of the signal improves the compliance of all the potential predators. Figure 6 shows a variety of foul-tasting butterflies with similar coloration, and some similar looking but good tasting butterflies which are taking advantage of this predator repelling coloration.

Figure 6. Several unpleasant-tasting butterfly species share a similar color pattern (mullerian mimicry) with better-tasting varieties (batesian mimicry), both examples of mimicry used to discourage predation. (Credit:  Joron M, Papa R, Beltrán M, Chamberlain N, Mavárez J, et al. accessed from OpenStax is licensed under CC BY 4.0)

5.2 Symbiosis – Close Interactions between Species

Symbiotic relationships, or symbioses (plural), are close interactions between individuals of different species over an extended period of time which impact the abundance and distribution of the populations interacting with each other. These interactions can be classified as commensalism, mutualism, and parasitism.

Commensal Relationships

A commensal relationship (commensalism) occurs when one species benefits from the close, prolonged interaction, while the other neither benefits nor is harmed. Birds nesting in trees provide an example of a commensal relationship (Figure 7). The tree is not harmed by the presence of the nest among its branches. The nests are light and produce little strain on the structural integrity of the branch, and most of the leaves, which the tree uses to get energy by photosynthesis, are above the nest so they are unaffected. The bird, on the other hand, benefits greatly. If the bird had to nest in the open, its eggs and young would be vulnerable to predators. Another example of a commensal relationship is the clownfish and the sea anemone. The sea anemone is not harmed by the fish, and the fish benefits with protection from predators who would be stung upon nearing the sea anemone.

 

Figure 7. The southern masked-weaver bird is starting to make a nest in a tree in Zambezi Valley, Zambia. This is an example of a commensal relationship, in which one species (the bird) benefits, while the other (the tree) neither benefits nor is harmed. (Credit:  “Hanay”/Wikimedia Commons accessed from OpenStax is licensed under CC BY 4.0)

Mutualistic Relationships

A second type of symbiotic relationship is called mutualism, where two species each benefit from their interaction. A commonly known example is the relationship between bees and flowers, where the bees obtain nutritional nectar, while the flowers benefit by having their pollen passed to other flowers on the body of the bees. Another example can be found in termites, which have a mutualistic relationship with protozoa that live in their gut (Figure 8a). The termite benefits from the ability of bacterial symbionts within the protozoa to digest cellulose from the wood it eats. The termite itself cannot break down cellulose, and without the protozoa, it would not be able to obtain energy from the wood it chews and eats. The protozoa and the bacterial symbionts benefit by having a protective environment inside the termite and a constant supply of food from the wood chewing actions of the termite. Lastly, lichens have a mutualistic relationship between fungus and photosynthetic algae or bacteria (figure 8b). As these symbionts grow together, the glucose produced by the algae provides nourishment for both organisms, whereas the physical structure of the lichen protects the algae from the elements and makes certain nutrients in the atmosphere more available to the algae.

Figure 8 (a) Termites form a mutualistic relationship with symbiotic protozoa in their guts, which allow both organisms to obtain energy from the cellulose the termite consumes. (b) Lichen is a fungus that has symbiotic photosynthetic algae living inside its cells. (Credit: a. modification of work by Scott Bauer, USDA; Attribution b. modification of work by Cory Zanker accessed from OpenStax is licensed under CC BY 4.0)

Parasitic Relationships

Parasites are organisms that live in or on another living organism and derive nutrients from it. In this relationship, the parasite benefits, but the host is harmed. The host is usually weakened by the parasite as it siphons resources the host would normally use to maintain itself. The parasite, however, is unlikely to kill the host, especially not quickly, because this would not allow time for the organism to complete its reproductive cycle and spread to another host.

The reproductive cycles of parasites are often very complex, sometimes requiring more than one host species. A tapeworm is a parasite that causes disease in humans when contaminated, undercooked pork is consumed (figure 9). The tapeworm can live inside the intestine of the host for several years, benefiting from the food the host is eating, and may grow to be over 50 ft long by adding segments. The parasite moves from species to species in a cycle, making two hosts necessary to complete its life cycle.

Figure 9. This diagram shows the life cycle of a pork tapeworm (Taenia solium), a human worm parasite. (Credit: modification of work by CDC accessed from OpenStax is licensed under CC BY 4.0)

The life cycle of a tapeworm begins when eggs or tapeworm segments in the feces are ingested by pigs or humans. The embryos hatch, penetrate the intestinal wall, and circulate to the musculature in both pigs and humans. Humans may acquire a tapeworm infection by ingesting raw or undercooked meat. Infection may result in cysts in the musculature, or in tapeworms in the intestine. Tapeworms attach themselves to the intestine via a hook-like structure called the scolex. Tapeworm segments and eggs are excreted in the feces, completing the cycle.

Another common parasite is Plasmodium falciparum, the protozoan that causes malaria, a significant disease in many parts of the world. Living in human liver and red blood cells, the organism reproduces asexually in the gut of blood-feeding mosquitoes to complete its life cycle. Thus malaria is spread from human to human by mosquitoes, one of many arthropod-borne infectious diseases.

5.3 Competition and the Competitive Exclusion Principle

Competition

Competition occurs when different organisms are seeking the same resources. The resource that is most in demand by competing species is usually food, whether that is grass, leaves, or other plant materials sought by herbivores, or animal prey, such as rabbits or rodents, sought by competing predators. For plants important resources include access to sunlight and the many key soil nutrients. Simply a space to live might be under competition, whether that is hole in a tree for nesting or a place to grow on the forest floor.

When competition is between members of the same species, this is referred to as intraspecific competition. For example, wildebeest compete for access to newly grown grasses during the rainy season, often spreading out across the savannah as they walk to avoid competition from other members of their species. Interspecific competion is between members of different species seeking the same resources. For example, both bears and mountain lions may seek the same prey and feed on available carrion, competing fiercely for these opportunities for sustenance.

Competitive Exclusion Theory

As explored above, resources are often limited within a habitat and multiple species may compete to obtain them (interspecific competition). All species have an ecological niche in the ecosystem, which describes how they acquire the resources they need and how they interact with other species in the community. The competitive exclusion principle states that two species cannot occupy the same niche in the same habitat. In other words, different species cannot coexist in a community if they are competing for all of the same resources. An example of this principle is shown in figure 10, with two protozoan species, Paramecium aurelia and Paramecium caudatum. When grown individually in the laboratory, they both thrive. But when they are placed together in the same test tube (habitat), P. aurelia outcompetes P. caudatum for food, leading to the latter’s eventual extinction.

This exclusion may be avoided if a population evolves to make use of a different resource, a different area of the habitat, or feeds during a different time of day, called resource partitioning. The two organisms are then said to occupy different microniches. These organisms coexist by minimizing direct competition.

Figure 10. Paramecium aurelia and Paramecium caudatum grow well individually, but when they compete for the same resources, the P. aurelia outcompetes the P. caudatum. (Credit:  “Competitive Exclusion in Paramecium” by OpenStax is licensed under CC BY 4.0)

Another interesting example of the competitive exclusion principle can be found among the tree dwelling lizards called anoles. A study in Puerto Rico noted that different anole species preferred different part of the vegetation they were living in, based on factors such as height within the vegetation, sunlight exposure and moisture. Although in close proximity to each other, each species had specialized on a different part of the vegetation (Figure 11).

Figure 11. Resource partitioning among anole lizards in Puerto Rico, which have specialized to thrive on different plants or different parts of large trees. (Source: LibreTexts Biology)

Intraspecific competition may lead to territorial behavior, such as when a hummingbird defends a particular area, preventing other members of its species from obtaining nectar or other resources from its territory. The male vicuña, a llama-like wild animal living in the high Andes of South America, defends a territory from other male vicuñas (Figure 12). In his territory are the females he mates with and his young, which are able to obtain food and water on the territory, and find safe places to sleep at night. Only territorial males who successfully compete against other males to maintain this territory are able to pass their genes to the next generation, since breeding females are always found on vicuña territories.

Figure 12. A male vicuña defends his territory from other males, due to intraspecific competition among adult males. This territory provides a protected area for females and their young (sired by the male) to graze, drink, and sleep. This photo shows a territorial male and 4 of its young (called crias). (Credit: Wikimedia Commons; agraria.pe)

5.4 Characteristics and Components of Communities

Communities are complex entities that can be characterized by their structure (the types and numbers of species present) and dynamics (how communities change over time). Understanding community structure and dynamics enables community ecologists to manage ecosystems more effectively.

Foundation Species

Foundation species are considered the “base” or “bedrock” of a community, having the greatest influence on its overall structure. They are usually the primary producers, organisms that bring most of the energy into the community. Kelp, for example, is a brown algae that is the foundation species of the kelp forests in the ocean off the coast of California.

Foundation species may physically modify the environment to produce and maintain habitats that benefit the other organisms that use them. An example is the photosynthetic corals of the coral reef (Figure 13). Corals themselves are not photosynthetic, but harbor symbionts within their body tissues (dinoflagellates called zooxanthellae) that perform photosynthesis; this is another example of mutualism. The exoskeletons of living and dead coral make up most of the reef structure, which protects many other species from waves and ocean currents.

Figure 13. Coral is the foundation species of coral reef ecosystems. (Credit: Jim E. Maragos, USFWS accessed from OpenStax is licensed under CC BY 4.0)

Keystone Species

A keystone species is one whose presence is key to maintaining biodiversity within an ecosystem and to upholding an ecological community’s structure. The intertidal sea star, Pisaster ochraceus, of the northwestern United States is a keystone species (Figure 14). Studies have shown that when this organism is removed from communities, populations of their natural prey (mussels) increase, completely altering the species composition and reducing biodiversity. Another keystone species is the banded tetra, a fish in tropical streams, which supplies nearly all of the phosphorus, a necessary inorganic nutrient, to the rest of the community. If these fish were to become extinct, the community would be negatively affected.

Figure 14. The Pisaster ochraceus sea star is a keystone species. (Credit: Jerry Kirkhart accessed from OpenStax is licensed under CC BY 4.0)

Video on and important keystone species, the beaver:

Moo Moo Math and Science (2020, May 6). Keystone Species – the Beaver. [Video – YouTube] https://youtu.be/Dd-Bslj_bOI

Video on Keystone Species: The following video on Keystone Species is excellent and easy to follow, but is not licensed to be embedded in this eBook. However, please follow the link to the author’s copywrited video to view this important video:

az.pbslearningmedia.org/resource/keystone-species-trophic-cascades/some-animals-are-more-equal-than-others-the-serengeti-rules/?student=true&focus=true

Invasive Species

Invasive species are nonnative organisms that, when introduced to an area out of their native range, threaten the ecosystem balance of the habitat they have entered. Many such species exist in the United States, as shown in figure 15. Whether enjoying a forest hike, taking a summer boat trip, or simply walking down an urban street, you have likely encountered an invasive species.

One of the many recent proliferations of an invasive species concerns the growth of Asian carp populations. Asian carp were introduced to the United States in the 1970s by fisheries and sewage treatment facilities that used the fish’s excellent filter feeding capabilities to clean their ponds of excess plankton. Some of the fish escaped, however, and by the 1980s they had colonized many waterways of the Mississippi River basin, including the Illinois and Missouri Rivers. Voracious eaters and rapid reproducers, Asian carp may outcompete native species for food, potentially leading to their extinction. For example, black carp eat native mussels and snails, limiting this food source for native fish species. Silver carp eat plankton that native mussels and snails feed on, reducing this food source by a different alteration of the food web. In some areas of the Mississippi River, Asian carp species have become the most predominant, effectively outcompeting native fishes for habitat. In some parts of the Illinois River, Asian carp constitute 95 percent of the community’s biomass. Although edible, the fish is bony and not a desired food in the United States. Moreover, their presence threatens the native fish and fisheries of the Great Lakes, which are important to local economies and recreational anglers. Asian carp have even injured humans. The fish, frightened by the sound of approaching motorboats, thrust themselves into the air, often landing in the boat or directly hitting the boaters.

Figure 15. In the United States, invasive species like (a) purple loosestrife (Lythrum salicaria) and the (b) zebra mussel (Dreissena polymorpha) threaten certain aquatic ecosystems. Some forests are threatened by the spread of (c) common buckthorn (Rhamnus cathartica), (d) garlic mustard (Alliaria petiolata), and (e) the emerald ash borer (Agrilus planipennis). The (f) European starling (Sturnus vulgaris) may compete with native bird species for nest holes. (Credit: Attribution: a: modification of work by Liz West; credit b: modification of work by M. McCormick, NOAA; credit c: modification of work by E. Dronkert; credit d: modification of work by Dan Davison; credit e: modification of work by USDA; credit f: modification of work by Don DeBold accessed from OpenStax is licensed under CC BY 4.0)

The Great Lakes and their prized salmon and lake trout fisheries are also being threatened by these invasive fish. Asian carp have already colonized rivers and canals that lead into Lake Michigan. One infested waterway of particular importance is the Chicago Sanitary and Ship Channel, the major supply waterway linking the Great Lakes to the Mississippi River. To prevent the Asian carp from leaving the canal, a series of electric barriers have been successfully used to discourage their migration; however, the threat is significant enough that several states and Canada have sued to have the Chicago channel permanently cut off from Lake Michigan. Local and national politicians have weighed in on how to solve the problem, but no one knows whether the Asian carp will ultimately be considered a nuisance, like other invasive species such as the water hyacinth and zebra mussel, or whether it will be the destroyer of the largest freshwater fishery of the world.

The issues associated with Asian carp show how population and community ecology, fisheries management, and politics intersect on issues of vital importance to the human food supply and economy. Socio-political issues like this make extensive use of the sciences of population ecology (the study of members of a particular species occupying a particular area known as a habitat) and community ecology (the study of the interaction of all species within a habitat).

Biodiversity

Biodiversity describes a community’s biological complexity: it is measured by the number of different species (species richness) in a particular area and their relative abundance (species evenness).

The area in question could be a habitat, a biome, or the entire biosphere. Species richness is the term that is used to describe the number of species living in a habitat or biome. Species richness varies across the globe (Figure 16).

One factor in determining species richness is latitude, with the greatest species richness occurring in ecosystems near the equator, which often have warmer temperatures, large amounts of rainfall, and low seasonality (Figure 16). The lowest species richness occurs near the poles, which are much colder, drier, and thus less conducive to life. The predictability of climate and its effect on productivity are also important factors. The study of island biogeography attempts to explain the relatively high species richness found in certain isolated island chains, including the Galápagos Islands that inspired the young Darwin. Relative species abundance is the number of individuals in a species relative to the total number of individuals of all species within a habitat, ecosystem, or biome. Foundation species often have the highest relative abundance of species.

Figure 16. The greatest species richness for mammals in North and South America is associated with the equatorial latitudes. (Credit: modification of work by NASA, CIESIN, Columbia University accessed from OpenStax is licensed under CC BY 4.0)

5.5 Community Dynamics

Community dynamics are the changes in community structure and composition over time. Sometimes these changes are induced by environmental disturbances such as volcanoes, earthquakes, storms, fires, and climate change. Communities with a stable structure are said to be at equilibrium – that is they can reach a point in time where there are no longer great changes in the flora and fauna of that particular location. Following a major disturbance, the community may or may not return to the equilibrium state.

Succession describes the sequential appearance and disappearance of species in a community over time. For example, after a fire in the Ponderosa pine forest of northern Arizona, grasses and small herbaceous plants may begin growing first, followed each year by larger shrubs and small trees, followed by the return many years later of the Ponderosa pines.

In primary succession, newly exposed or newly formed land is colonized by living things, such as on newly formed volcanic islands. In secondary succession, an existing ecosystem may be disturbed by human or other influences, such as the wildfire described above, but if left alone, may slowly return to its former state.

Primary succession occurs when new land is formed or rock is exposed, and living things begin growing in this newly formed land. For example, following the eruption of volcanoes, such as those on the Big Island of Hawaii, new life may form on the exposed rock that has cooled on land or in the nearby ocean. Approximately 32 acres of land is added each year to the Big Island because of volcanic activity affecting nearby waters. First, weathering and other natural forces break down the newly formed rock enough for the establishment of certain hearty plants and lichens with few soil requirements, known as pioneer species (Figure 17). These species help to further break down the mineral rich lava into soil where other, less hardy species will grow and eventually replace the pioneer species. In addition, as these early species grow and die, they add to an ever-growing layer of decomposing organic material and contribute to soil formation. Over time the area will reach an equilibrium state, with a set of organisms quite different from the pioneer species.

Figure 17. During primary succession in lava on Maui, Hawaii, succulent plants are the pioneer species. (Credit: Forest and Kim Starr accessed from OpenStax is licensed under CC BY 4.0)

Secondary succession occurs when an ecosystem is disturbed by natural means (e.g., fires or floods) or by human activities (e.g. timber cutting, land clearing), and the land then returns to its natural state.   A classic example of secondary succession occurs in oak and hickory forests cleared by wildfire. Wildfires will burn most vegetation and kill those animals unable to flee the area. Their nutrients, however, are returned to the ground in the form of ash. Thus, even when areas become devoid of life due to severe fires, the area will soon be ready for new plants and other life forms to take hold, as illustrated in Figure 18. 

Figure 18. Secondary succession is shown in an oak and hickory forest after a forest fire. (Credit: “Secondary Succession of an Oak and Hickory Forest” by OpenStax is licensed under CC BY 4.0)

Before the fire, the vegetation was dominated by tall trees with access to the major plant energy resource: sunlight. Their height gave them access to sunlight while also shading the ground and other low-lying species. After the fire, though, these trees are no longer dominant. Thus, the first plants to grow back are usually annual plants followed within a few years by quickly growing and spreading grasses and other pioneer species. Over the years, as the environment changes with the growth of grasses and other low lying species, shrubs may emerge along with small pine, oak, and hickory trees. These organisms are called intermediate species. Eventually, a time period that may exceed 100 years, the forest will reach its equilibrium point, where species composition is no longer changing greatly and resembles the community before the fire. This equilibrium state is referred to as the climax community, which will remain relatively stable until the next disturbance.

Attribution:

Content in this chapter includes original work created by Lauren Roberts and Paul Bosch as well as from the following sources, with some modifications:

“Biology, 2nd edition” by OpenStax is licensed under CC BY 4.0 / A derivative from the original work