Herbivorous
In zoology, a herbivore is an animal that feeds mainly on plants. In practice, many mainly herbivorous animals also feed on animal proteins, such as insects, eggs, etc. In the food chain, herbivores are the primary consumers, while meat eaters are secondary consumers. People who do not eat meat are not considered herbivores, but rather vegetarians.
Some herbivores can be classified as frugivores, which eat mostly fruit, and folivores, which specialize in eating leaves. This specialization is far from universal, and many animals that eat fruit or leaves also eat other parts of plants, particularly roots and seeds. The diets of some herbivorous animals vary with the seasons, especially in temperate zones, where available food sources vary throughout the year. Animals that feed on the leaves of trees and shrubs are sometimes called leaf eaters or browsers. Wood-eating animals are called xylophages, while seed-eating animals are called granivores.
The most important group of herbivorous mammals is made up of ruminants, those animals that digest food in two stages, first they consume it and then they ruminate. This consists of regurgitating the semi-digested material and chewing it again to break it down and add saliva. Their jaw allows them to make lateral movements to be able to crush and salivate food. Their molars are very flat, and allow food to be crushed into a paste. Their saliva gives an alkaline reaction, which allows them to better digest carbohydrates. The intestinal flora has a very important role in the digestion of plant materials.
Insects are perhaps the most important group of herbivores for their impact on vegetation. Termites have a rich and complex intestinal flora that allows them to digest extremely difficult-to-digest materials such as cellulose. Aphids or aphids feed on plant fluids and are very abundant both in number of individuals and in number of species. The caterpillars of virtually all Lepidopteran species are herbivorous and, in certain cases, can cause defoliation of entire forests.
Plant-Herbivore Interactions
Plant-herbivorous interactions may play a predominant role in ecosystem dynamics such as community structure and functional processes. Plant species diversity and distribution are often driven by herbivory, and it is likely that trade-offs between plant competitiveness and ability to defend themselves, and between colonization and mortality allow for coexistence between species in the presence of herbivores. However, the effects of herbivory on diversity and richness of plants is variable. For example, increased abundance of herbivores such as deer decreases plant diversity and species richness, while other large herbivorous mammals such as bison control dominant species allowing other species to thrive. Interactions between Plants and herbivores can also operate in such a way that plant communities mediate herbivore communities. Plant communities that are more diverse tend to support greater herbivore richness by providing a larger and more diverse pool of resources.
Coevolution and phylogenetic correlation between herbivores and plants are important aspects of the influence of herbivore-plant interactions on communities and ecosystem functioning, especially as regards herbivorous insects. This it is evident in the adaptations that plants develop to tolerate and/or defend against insect herbivory and the responses of herbivores to overcome these adaptations. The evolution of antagonistic and mutualistic interactions between plants and herbivores are not mutually exclusive and may coincide. Plant phylogeny has been shown to facilitate the colonization and assembly of herbivore communities, and there is evidence for phylogenetic linkage between plants. the beta diversity of plants and the beta diversity of clades of insects, such as butterflies. This type of eco-evolutionary feedback between plants and herbivores is probably the main driving force of plant and herbivore diversity.
Abiotic factors such as climate and biogeographical features also influence communities and interactions between plants and herbivores. For example, in temperate freshwater wetlands, aquatic herbivore communities change seasonally, with species that feed on aboveground vegetation being abundant in summer, and species that feed below ground being present. in winter months. These seasonal herbivore communities differ in both their assemblage and functions within the wetland ecosystem. These differences in herbivore patterns can potentially lead to tradeoffs that influence species traits and can lead to additive effects on community composition and ecosystem functioning. Seasonal changes and environmental gradients, such as elevation and latitude, often affect plant palatability, which in turn influences in assemblages of herbivore communities and vice versa. Examples include a decline in the abundance of chewing larvae leaf worshipers in the fall when the palatability of hardwood leaves decreases due to increased tannin levels resulting in decreased arthropod species richness, and increased palatability of plant communities a higher elevations, where grasshopper abundance is lower. Climatic stressors, such as ocean acidification, may also trigger responses in plant-herbivorous interactions regarding palatability.
Gerbivore Offense
The myriad defenses that plants present mean that their herbivores need a series of skills to overcome these defenses and obtain food. This allows herbivores to increase their feeding and use of a host plant. Herbivores have three main strategies to deal with plant defenses: choice, herbivore modification, and plant modification.
Food choice involves which plants an herbivore chooses to consume. It has been suggested that many herbivores feed on a variety of plants to balance their nutrient intake and avoid consuming too much of one type of defensive chemical. However, this involves a trade-off between eating many plant species to avoid toxins or specializing in one type of plant that can be detoxified.
Herbivorous modification occurs when various adaptations of the body or digestive systems of herbivores allow them to overcome plant defenses. This can include detoxification of secondary metabolites, sequestering toxins unchanged, or avoidance of toxins, for example by producing large amounts of saliva to reduce the effectiveness of defenses. Herbivores can also use symbiotes to evade plant defenses. For example, some aphids use bacteria in their gut to provide essential amino acids that are missing from their sap diet.
Plant modification occurs when herbivores manipulate their plant prey to increase their diet. For example, some caterpillars roll up their leaves to reduce the effectiveness of plant defenses activated by sunlight.
Defense of plants
A plant defense is a trait that increases a plant's fitness when faced with herbivory. This is measured relative to another plant that lacks the defensive trait. Plant defenses increase the survival and/or reproduction (fitness) of plants under the pressure of predation by herbivores.
Defense can be divided into two main categories, tolerance and resistance. Tolerance is the ability of a plant to withstand damage without a reduction in fitness. This can occur by diverting herbivory to non-essential plant parts, resource allocation, compensatory growth, or by rapid regrowth and shedding. herbivory recovery. Resistance refers to a plant's ability to reduce the amount of damage it receives from herbivores. This can occur through avoidance in space or time, physical defenses, or defenses chemicals. Defenses can be constitutive, always present in the plant, or induced, produced or translocated by the plant after damage or stress.
Physical, or mechanical, defenses are barriers or structures designed to deter herbivores or reduce ingestion rates, decreasing overall herbivory. Thorns and spikes, such as those found on roses or acacias, are one example, as are cactus spines. Smaller hairs known as trichomes can cover the leaves or stems and are especially effective against invertebrate herbivores. Additionally, some plants have waxes or resins that alter their texture, making them difficult to eat. Also the incorporation of silica into cell walls is analogous to the role of lignin in that it is a compression-resistant structural component of cell walls; so that plants with their cell walls impregnated with silica thus receive a measure of protection against herbivory.
Chemical defenses are secondary metabolites produced by the plant that deter herbivory. There are a wide variety of them in nature and a single plant can have hundreds of different chemical defenses. Chemical defenses can be divided into two main groups, carbon-based defenses and nitrogen-based defenses.
- Carbon-based defenses include terpenes and phenolics. Terpenes are derived from 5-carbon isoprene units and include essential oils, carotenoids, resins and latex. They may have several functions that disturb herbivores, such as inhibiting the formation of adenosine triphosphate (ATP), mute hormones or nervous system. Phenolics combine an aromatic carbon ring with a hydroxyl group. There are several different phenolics, such as lignins, which are found on the cell walls and are very unworthy, except for specialized microorganisms; tannins, which have a bitter taste and bind to proteins making them unworthy; and furanocumerins, which produce free radicals that alter DNA, proteins and lipids, and can cause skin irritation.
- Nitrogen-based defenses are synthesized from amino acids and are mainly presented in the form of alkaloids and cyanogens. Alkaloids include commonly recognized substances such as caffeine, nicotine and morphine. These compounds are usually bitter and may inhibit DNA or RNA synthesis or block the transmission of signals from the nervous system. Cyanogens receive their name from cyanide stored in their tissues. This is released when the plant is damaged and inhibits cell breathing and electron transport.
Plants have also changed characteristics that increase the likelihood of attracting the natural enemies of herbivores. Some emit semiochemicals, odors that attract natural enemies, while others provide food and shelter to maintain the presence of natural enemies, for example ants that reduce herbivory. A certain plant species usually has many types of defensive mechanisms, mechanical or chemical, constitutive or induced, that allow it to escape from herbivores.
Predator-Prey Theory
According to the theory of predator-prey interactions, the relationship between herbivores and plants is cyclical. When prey (plants) are numerous, their predators (herbivores) increase in number, reducing the prey population, thus in turn causes the number of predators to decrease. The prey population eventually recovers, starting a new cycle. This suggests that the population of the herbivore fluctuates around the carrying capacity of the food source, in this case, the plant.
Several factors intervene in these fluctuating populations that contribute to stabilizing the predator-prey dynamic. For example, spatial heterogeneity is maintained, which means that there will always be pockets of plants that herbivores cannot find. This stabilizing dynamic plays an especially important role for specialist herbivores that feed on a plant species and prevents these specialists from destroying their food source. Prey defenses also help stabilize the dynamic between predators and prey, and for more information on these relationships see the section on plant defenses. Eating a second type of prey helps stabilize herbivore populations. Switching between two or more types of plants provides population stability to the herbivore, while plant populations fluctuate. This plays an important role for generalist herbivores that They eat a variety of plants. Keystone herbivores keep vegetation populations in check and allow for greater diversity of both herbivores and plants. When a herbivore or invasive plant enters the system, the balance is upset and diversity can collapse into a system. monotaxonic.
The back-and-forth relationship between plant defense and herbivore offense drives coevolution between plants and herbivores, leading to a "coevolutionary arms race". The mechanisms escape and radiation for coevolution, presents the idea that adaptations in herbivores and their plant hosts have been the driving force behind speciation.
Mutualism
Although much of the interplay between herbivory and plant defense is negative, as one individual reduces the fitness of the other, another part is beneficial. This beneficial herbivory takes the form of mutualisms in which both partners benefit in some way from the interaction. Seed dispersal by herbivores and pollination are two forms of mutualistic herbivory in which the herbivore is provided with a food resource and the plant is aided in its reproduction. Plants can also be affected indirectly by herbivores through nutrient recycling, with plants benefiting from herbivores when nutrients are recycled very efficiently. Another form of plant-herbivore mutualism is physical changes to the environment and/or plant community structure by herbivores. herbivores that serve as ecosystem engineers, such as wallowing by bison. Swans form a mutual relationship with foraging plant species by digging and disturbing the sediment, which eliminates competing plants and subsequently allows colonization of other plants. other plant species.