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EcoEco Ch.1-17Review
EcoEco Ch.1-ReviewQs
| Ecological Systems exist in a hierarchical organization. | The hierarchy begins with individual organisms and moves up through higher levels of complexity including populations, communities, ecosystems, and the biosphere. At each of these levels, ecologists study different types of processes. |
| Ecological systems are governed by physical and biological principles. | These principles include the conservation of matter and energy, dynamic steady states, a requirement to expend energy, and the evolution of new phenotypes and new species. |
| Different organisms play diverse roles in ecological systems. | The major groups of organisms are plants, animals, fungi, protists, & bacteria. They're involved in numerous species interactions- competition, predation, mutualism, & commensalism. Each organism lives in specific habitats and has a particular niche. |
| Scientists use several approaches to studying ecology. | Like all scientists, ecologists use the scientific method of developing and testing hypotheses. Testing of proximate and ultimate hypotheses can be accomplished using manipulative experiments, natural experiments, or mathematical models. |
| Humans influence ecological systems. | The rapid growth of the human population during the past two centuries has increased human influence on ecological systems, particularly as the result of resources they consume and waste products they release. |
| Water has many properties favorable to life. | These include thermal resistance to changes in temperature, a density and viscosity that select for adaptions for movement, and the ability to dissolve many elements and compounds that are essential to life. |
| Aquatic environments challenge the balance of water and salt in animals. | This challenge occurs because animal tissues are generally hyperosmotic or hyposmotic compared to the solute concentration of the surrounding aquatic environment.` |
| The uptake of gases from the water is limited by diffusion. | This limitation can make it difficult for organisms to exchange gases such as CO2 and O2. Diffusion is slowed because organisms are surrounded by a thin boundary layer of unstirred water. Although CO2 can be abundant in water - either as a dissolved gas o |
| Temperature limits the occurrence or aquatic life. | Although warmer temperatures increase the rate of chemical reactions, excessively high temperatures cause proteins and other important molecules to become unstable and denature. Organisms that live under a wide range of temperature often use isozymes to |
| permit proper physiological function at each temperature. Cold temperatures also pose a challenge and many organisms living under near-freezing conditions have evolved adaptations that include the use of glycoproteins and supercooling to prevent the | harmful effects of ice crystals growing inside their cells. |
| Most terrestrial plants obtain nutrients and water from the soil. | Soil nutrients include nitrogen, phosphorus, calcium, and potassium. The water-holding capacity of soil, known as its field capacity, depends on the particle sizes in the soil. The ability of plants to absorb this water requires that the osmotic potential |
| of the roots be stronger than the matrix potential of the soil. This water moves up the plant stem to its leaves through a combination of osmotic pressure, the cohesion of water molecules, and the force of transpiration. | Sunlight provides the energy for photosynthesis. |
| Within the full range of electromagnetic radiation produced by the Sun, only a narrow range of wavelengths is used by the photosynthetic pigments of plants. This solar energy is used to power the process of photosynthesis by splitting water molecules and | producing molecular oxygen and sugar. There are three pathways of photosynthesis: C3, C4, and CAM. Each differs in how it captures CO2 and each works best in particular environmental conditions. These different pathways are often associated with |
| structural adaptations that help plants from arid regions conserve water. | Terrestrial environments pose a challenge for animals to balance water, salt, and nitrogen. |
| Organisms attempt to achieve homeostasis in all of these compounds, typically through the use of negative feedbacks. Plants and animals both possess a number of adaptations to balance their concentrations of salt, water, and nitrogenous wastes. | Adaptations to different temperatures allow terrestrial life to exist around the planet. |
| Organisms can gain and lose heat through radiation, conduction, convection, and evaporation. These processes combine to form an individual's heat budget. Temperature can be regulated to different degrees by animals through the process of thermoregulation. | Poikilotherms have variable body temps vs homeotherms have relatively constant body temps. The temps of ectotherms are largely determined by their external environment whereas endotherms can raise their body temps higher than the external environment. |
| Additional adaptations to assist in thermoregulation include the shunting of blood and countercurrent circulation. | Ecological systems and processes vary in time and space. |
| Temporal variation occurs across a range of hours to years with the most extreme variation being the least frequent. Spatial variation also exists due to diffs in climate, topography, & soils. The extent of the space affected by an event is usually | positively related to an event's duration in time. |
| Variable environments favor the evolution of variable phenotypes. | Phenotypic plasticity, the ability to produce alternative phenotypes, is favored when organisms experience environmental variation, when reliable cues indicate the current state of the environment &when no single phenotype is superior in all environments. |
| Phenotypically plastic traits include behavior, physiology, morphology, and life history. Each type of trait differs in how fast it can respond to environmental change and whether the responses are reversible. | Many organisms have evolved adaptations to variation in enemies, competitors, and mates. |
| Responses to enemies include changes in behavior that make individuals harder to detect, morphological defense that makes prey harder to capture, and chemical defenses that makes prey less palatable. Responses to competitors include morphological changes | in plants to help them obtain resources, morphological changes in animals that help them to consume and digest scarce food, & behavioral strategies in animals that help them find scarce food. Organisms generally favor breeding with another individual, |
| but a scarcity of mates can make self-fertilization a viable alternative for some species. | Organisms can evolve adaptations to variable abiotic conditions. |
| Variation in temp has favored the evolution of isozymes and switching between microhabitats. Variation in water availability has favored plants that can open and close their stomata and alter their root:shoot ratios. Variation in salinity has favored the | evolution of novel ways of adjusting solute concentrations to minimize the cost of osmoregulation. Variation in oxygen can cause adaptive increases in red blood cells and hemoglobin to improve the uptake of oxygen at high altitudes. |
| Migration, storage, and dormancy are strategies used to survive extreme environmental variation. | Migration allows organisms to leave areas with degrading environments, storage allows organisms to have an extra supply of energy to make it through periods of degrading environments. Dormancy allows organisms to shut down their metabolism until the |
| harmful environmental conditions have passed. | Variation in food quality and quantity is the basis of optimal foraging theory. |
| Central place foraging predicts that the amount of time spent foraging at a site and the amount of food brought back to a central nest will depend on the benefits gained over time at the site and the round-trip travel time to the site. Risk-sensitive | foragers consider not only the energy to be gained, but also the predation risk posed. Many animals must also consider a range of alternative food items, the energy and abundance of each food item, and whether they should consume a mixture of food items |
| to meet all of their nutritional needs. | The unequal heating of Earth drives air currents in the atmosphere. |
| Due to the properties of air, the warmer temps near the equator drive atmospheric convection currents known as Hadley cells between approximately 0 to 30 degrees latitude. in the Northern and Southern Hemispheres. Polar cells are at higher latitudes, | between approximately 60-90 degrees. These air convection currents cause the distribution of heat and precipitation around the globe. Their path is also influenced by Coriolis forces that are created by the rotation of Earth. |
| Ocean currents also affect the distribution of climates. | Ocean currents are driven by the unequal warming of Earth combined with Coriolis effects, atmospheric convection currents, and differences in salinity. Gyres exist on both sides of the equator and help distribute heat and nutrients to higher latitudes. |
| El Nino-Southern Oscillation (ENSO) events represent a disruption in normal ocean currents in the South Pacific and the impacts on climates can be felt around the world. Thermohaline circulation is a deep and slow circulation of the world's oceans driven | by changes in salt concentration in the waters of the North Atlantic. |
| Smaller-scale geographic features can affect regional and local climates. | Increased land area of continents reduces the amount of evaporation possible, which causes the Northern Hemisphere to experience less precipitation than the Southern Hemisphere. Proximity to the coast can also affect climates; regions that are more |
| distant from coastlines typically have lower precipitation and higher variation in temps. Mountain ranges force air to rise over them, causing higher precipitation on one side of the mountain range and rain shadows on the opposite side. | Climate and the underlying bedrock interact to create a diversity of soils. |
| Soils are comprised of horizons that contain different amounts of organic matter, nutrients, and minerals. Soils can be weathered by processes including freezing, thawing, and leaching. In acidic soils of cool, moist regions, soils can experience | podsolization, a process that breaks down clay particles and reduces fertility. In warm, humid climates, soils can experience laterization, a process that breaks down clay particles and leaches nutrients from the soil. |
| Earth is warmed by the greenhouse effect. | Much of the ultraviolet and visible light emitted by the Sun passes through the atmosphere and strikes clouds and the surface of Earth. Clouds and the planet begin to warm and emit infrared radiation back toward the atmosphere. The gasses in the |
| atmosphere absorb the infrared radiation, become warmer, and re-emit infrared radiation back toward Earth. These greenhouse gases allow the planet to become warmer than would otherwise be possible. The increase in production of greenhouse gases due to | human activities increases the greenhouse effect and leads to global warming. |
| There is an unequal heating of Earth by the Sun. | Each year, high latitude regions of the world receive solar radiation that is weaker in intensity due to a longer path through the atmosphere with a less direct angle, which causes the energy of the Sun to be spread over a larger area. In addition, the |
| axis of Earth is tilted 23.5 degrees and this causes seasonal changes in temperature. | Terrestrial biomes are categorized by their major plant growth forms. |
| Ecologists use the dominant plant forms to categorize ecosystems into terrestrial biomes because many plants have evolved convergent forms in response to similar climate conditions. Climate and dominant plant forms are similar within biomes. | There are nine categories of terrestrial biomes. |
| The coldest biomes are the tundra and boreal forests. In temperate regions, we can find temperate rainforests, temperate seasonal forests, woodlands/shrublands, and temperate grasslands/cold deserts. In tropical latitudes, the biomes can be categorized as | tropical rainforests, tropical seasonal forests/savannas, and subtropical deserts. |
| Aquatic biomes are categorized by their flow, depth, and salinity. | Freshwater biomes include streams and rivers, ponds and lakes, and freshwater wetlands. Saltwater biomes include salt marshes/estuaries, mangrove swamps, intertidal zones, coral reefs, and the open ocean. |
| The process of evolution depends on genetic variation. | Among and within populations, genetic variation is caused by the presence of different alleles, which can be dominant, codominant, or recessive. Genetic variation can be generated through mutation or recombination. |
| Evolution can occur through random processes or through selection. | The four random processes that cause evolution are mutation, genetic drift, bottleneck effects, and founder effects. Evolution can also occur by selection, which can be stabilizing, directional, or disruptive. Whether evolution occurs by random processes |
| or by selection, scientists can use similarities in traits to arrange hypothesized patterns of relatedness among different groups on phylogenetic trees. | Microevolution operates at the population level. |
| Populations can evolve due to artificial selection to produce breeds of domesticated animals and plants.Populations can also evolve due to natural selection, such as when predators selectively consume prey and when pesticides and antibiotics selectively | kill the most sensitive individuals, allowing the most resistant individuals to survive and reproduce. |
| Macroevolution operates at the species level and higher levels of taxonomic organization. | The most common process causing macroevolution is allopatric speciation in which populations become geographically isolated and independently evolve to become distinct species over time.The less common process is sympatric speciation in which species |
| become reproductively isolated without being geographically isolated, often by forming polyploids. | Life history traits represent the schedule of an organism's life. |
| Species differ in a wide range of traits that help determine their fitness throughout their life including the birth or hatching of offspring, the time required to reach sexual maturity, fecundity, parity, and longevity. These traits are under the | influence of natural selection and often evolve in particular combinations. |
| Life history traits are shaped by trade-offs. | Trade-offs can occur because of physical constraints, time or energetic constraints that affect allocation, or genetic correlations that cause selection favoring one trait to come at the cost of another trait. Common trade-offs include offspring number |
| versus offspring size, and growth versus reproduction. | Organisms differ in the number of times that they reproduce, but they all eventually become senescent. |
| Semelparous organisms breed once in their life whereas iteroparous organisms breed more than once. Regardless of how many times an organism breeds, it ultimately experiences a decay in physiological function followed by death. In semelparous organisms, | this decay in function occurs rapidly after reproduction. In iteroparous organisms, the decay in function can be very gradual. |
| Life histories are sensitive to environmental conditions. | As with all phenotypes, life history traits are the product of genes and environments interacting. Some of the most common environmental influences on life history predators, both of which can induce substantial changes in the life history of organisms. |
| Current anthropogenic changes in the environment can also affect life history traits by altering environmental cues-such as temps- that induce life history changes. | Reproduction can be sexual or asexual. |
| Asexual reproduction can either be through vegetative reproduction or through parthenogenesis. Compared to asexual reproduction, sexual reproduction results in fewer copies of a parent's genes in the next generation. This can be offset by adopting a | hermaphrodite sexual strategy or by providing parental care that results in raising twice as many offspring. The benefits of sexual reproduction include purging harmful mutations and creating genetic variation to help offspring deal with future |
| environmental variation. | Organisms can evolve as separate sexes or as hermaphrodites. |
| If an individual possessing only male or female function can add a large amount of the other sexual function while giving up only a small amount of its current sexual function, selection will favor the evolution of hermaphrodites. If not, selection will | favor the evolution of separate sexes. To avoid inbreeding depression, hermaphrodites have evolved adaptations to prevent selfing and mixed strategies for when selfing is the best option. |
| Sex ratios of offspring are typically balanced, but they can be modified by natural selection. | Depending on the species, sex may be largely determined by genetics or by the environment. In many species, females have the ability to manipulate the sex ratio by controlling which sperm are used to fertilize the eggs or which sex chromosomes end up in |
| the eggs, or by selective abortion of the fertilized embryos. In most organisms, the sex ratio is approximately one to one due to frequency-dependent selection. When offspring are isolated from the rest of the population and are subjected to local mate | competition, highly skewed offspring sex ratios can be adaptive. |
| Mating systems describe the pattern of mating between males and females. | While many species are socially monogamous, recent studies have demonstrated that many individuals participate in extra-pair copulations. |
| As a result of this infidelity, species have evolved a variety of mate guarding behaviors to prevent a reduction in their fitness. | Sexual selection favors traits that facilitate reproduction. |
| The difference in the energetic costs of gametes and the costs of parental care typically causes female fitness to be a function of mate quality and male fitness to be a function of mate quantity. As a result, females are typically selective in choosing | mates whereas males compete strongly with each other to mate as often as possible. Male competition for mates has favored the evolution of sexually dimorphic traits including body size, ornaments, coloration, and courtship behaviors. Females choose |
| particular males to obtain material benefits, such as nesting sites or food, or for nonmaterial benefits, such as good genes or good health. The best reproductive choices of males and females are often not reciprocal, which can cause conflicts between the | sexes. |
| Living in groups has costs and benefits. | The benefits of social living include the dilution effect in which large groups of prey have a reduced likelihood of being killed by a predator, reduced need for personal vigilance, and increased ability to find food and mates. The costs include an |
| increase in visibility to predators, increased frisk of parasite and pathogen transmission, and increased competition for food. In response to social living, many species have evolved the ability to establish territories and dominance hierarchies to | manage individual interactions. |
| There are many types of social interactions. | When we envision interactions in terms of donors and recipients, we can devise four types of social interactions: cooperation, selfishness, spitefulness, and altruism. Cooperation and selfishness of donors should be favored by natural selection whereas |
| spitefulness should not. Altruism can be favored when the recipient of an altruistic act is closely related to the donor, as measured by the coefficient of relatedness. | Eusocial species take social interactions to the extreme. |
| Eusocial animals consist of many individuals living together with dominant individuals reproducing and subordinate individuals forgoing reproduction. Eusocial species are common among the haplodiploid species of bees, ants, and wasps, but also exist in | diploid species of termites and at least two species of mammals. A high coefficient of relatedness favors the evolution of eusocial behavior, but it is not required. Equally important may be the presence of a low cost of lost fitness in species that have |
| a low probability of leaving the group and reproducing on their own. | The distribution of populations is limited to ecologically suitable habitats. |
| The range of suitable abiotic conditions where individuals can persists represents the fundamental niche of a species. The subset of conditions where a species actually persists due to biotic interactions is known as the realized niche. With an | understanding of the realized niche, ecologists can use ecological niche modeling to predict the areas in which a species could persists if it were to be introduced. |
| Population distributions have five important characteristics. | The geographic range of a population is a measure of the total area it covers. The abundance of a population is the total number of individuals that exist within a defined area. The density of a population is the number of individuals per unit area or |
| volume. Dispersion of a population describes the spacing of individuals with respect to one another. Dispersal is the movement of individuals from one area to another.q | The distribution properties of populations can be estimated. |
| These properties are typically measured by using a variety of survey techniques including area- and volume-based studies, line-transect studies, and mark-recapture studies. | Populations abundance and density are related to geographic range and adult body size. |
| There is generally a positive relationship between the abundance of a population and the size of its geographic range, although many other biotic and abiotic factors play a role in determining geographic range size. There is commonly a negative | relationship between adult body size and the density of a population because larger individuals require more energy. |
| Dispersal is essential to colonizing new areas. | Many populations do not inhabit suitable habitats because they are dispersal limited. One of the key ways to facilitate dispersal is through the creation of habitat corridors. |
| Many populations live in distinct patches of habitat. | The ideal free distribution makes predictions about how individuals should distribute themselves if they were to equalize the per capita benefits, although this is rarely observed in nature due to the importance of other factors such as predators and |
| territoriality. Ecologists have used three types of population structure models: the metapopulation model, the source-sink model, and the landscape model. | Under ideal conditions, populations can grow rapidly. |
| When populations grow at their intrinsic growth rate, they can initially increase at exponential rates, which can be modeled using either the exponential growth model or the geometric growth model. | Populations have growth limits. |
| The limits can be due to density-independent factors, which regulate population sizes regardless of the population's density. The limits can also be due to density-dependent factors, which affect population growth in a way that is related to the | population's density. Negative density dependence causes populations to grow more slowly as they become larger whereas positive density dependence causes populations to grow faster as they become larger. Ecologists use the logistic growth model to |
| demonstrate negative density dependence. The logistic model mimics rapid population growth when populations are small and slow population growth when populations approach their carrying capacity. The logistic growth model has been used to predict human | human population growth, but human populations have exceeded these predictions due to improvements in food production, international trade, and public health. |
| Population growth rate is influenced by the proportions of individuals in different age, size, and life history classes. | Most organisms have rates of survival and fecundity that change over their lifetime, as illustrated by survivorship curves. Life tables were developed to incorporate age-, size-, or life history-specific rates of survival and fecundity. Using life tables, |
| we can determine survivorship (lx), net reproductive rates (R0), generation times (T), and approximations of the intrinsic growth rates (r a and lambda a). The data needed for life tables can be collected by following a cohort and building a cohort life | table or by examining all individuals during a snapshot in time and developing static life tables. |
| Populations fluctuate naturally over time. | The occurs because density-dependent and density-independent factors can change from year to year and from place to place. The magnitudes of the fluctuations are often related to the ability of a species to resist changes in the environment and the |
| differences in their life histories, including reproductive rates and life span. In some species, the population can overshoot its carrying capacity and then experience a rapid die-off. In populations that have an age structure, fluctuations in population | size over time can be detected by disproportionate numbers of individuals in particular age classes. Many species experience cyclic fluctuations in population size. |
| Density dependence with time delays can cause populations to be inherently cyclic. | Delayed density dependence allows populations to fluctuate above and below their carrying capacity. Delayed density dependence can be incorporated into our population models by having the population's growth rate depend on the population density that |
| occurred at some time in the past. Using these model,s, we find that the magnitude of the fluctuations depends of the product of the intrinsic growth rate (r) and the time delay (tau). Increasing values of this product causes the population to shift | from experiencing no oscillations to damped oscillations to a stable limit cycle. Experiments have confirmed that time delays due to energy reserves or development times between life stages can cause cyclic fluctuations. |
| Chance events can cause small populations to go extinct. | Smaller populations are more likely to go extinct than large populations. This occurs due to demographic and environmental stochasticity. |
| Metapopulations are composed of subpopulations that can experience independent population dynamics across space. | Metapopulations exist when a habitat exists in small fragments, either naturally or from human activities. The basic model of metapopulation dynamics informs us that metapopulations persist due to a balance between extinctions in some habitat patches and |
| colonizations that occur in other patches. Although the basic metapopulation model assumes that all patches are equal, in reality, larger patches generally contain larger subpopulations and patches that are less isolated are more likely to be occupied as | a result of both the rescue effect and higher rates of recolonization. |
| Predators and herbivores can limit the abundance of populations. | Using observations in nature and manipulative experiments, ecologists have found that predators commonly limit the abundance of prey and herbivores commonly limit the abundance of producers. |
| Populations of consumers and consumed populations fluctuate in regular cycles. | Cycling populations have been observed frequently in nature and recreated in laboratory experiments. Lags in the response times of predator movement and reproduction linked to changes in the abundance of prey cause these cycles. Mathematical models have |
| been developed to mimic the cycling behavior of predator and prey populations. | Predation and herbivory favor the evolution of defenses. |
| Prey have evolved a wide variety of defenses including behavioral defenses, mechanical defenses, chemical defenses, crypsis, and mimicry. Producers have evolved defenses against herbivores including mechanical defenses, chemical defenses, and tolerance. | Evolved defenses are commonly costly and can sometimes be countered by subsequent adaptations in predators. |
| Many different types of parasites affect the abundance of host species. | Ectoparasites live on host organisms whereas endoparasites live in host organisms. As a group, parasites include a wide range of species that include plants, fungi, protozoa, helminths, bacteria, viruses, and prions. Among parasites that cause diseases - |
| known as pathogens - those that have recently become abundant are called emerging infectious diseases. | Parasite and host dynamics are determined by the parasite's ability to infect the host. |
| The transmission of parasites can be horizontal- either through direct transmission or transmission by a vector- or vertical from parent to offspring. The ability to infect a host also depends on the parasite's mode of entering the host, its ability to | infect a host also depends on the parasite's mode of entering the host, its ability to infect reservoir species, its ability to jump to new host species, and its ability to avoid the host's immune system. |
| Parasite and host populations commonly fluctuate in regular cycles. | These fluctuations occur because transmission increases with host density but decreases as an increased proportion of the host population develops immunity. These fluctuations can be modeled using the S-I-R model. |
| Parasites have evolved offensive strategies while hosts have evolved defensive strategies. | Natural selection has favored parasites that can improve their probability of transmission, including manipulations of host behavior. Hosts have evolved both specific and general immune responses to combat host infection. Hosts also can employ mechanical |
| and biochemical defenses against parasites. Coevolution occurs when the parasite and host continually evolve in response to each other. | Competition occurs when individuals experience limited resources. |
| Competition can either be intraspecific or interspecific and occurs when there is a limited resource. Resources can either be renewable or nonrenewable and they can be generated either from within an ecosystem or from outside an ecosystem. Leibig's laws | of the minimum states that a population will increase until the most limiting resource prevents further growth, although we now appreciate that different resources can have interactive effects on population growth. The competitive exclusion principle |
| states that two species cannot coexist indefinitely when they are both limited by the same resource. | The theory of competition is an extension of logistic growth models. |
| The simplest models consider competition for a single resource and consider the zero population growth isoclines of two competing species. Using these models, we can make predictions regarding the conditions under which two species can win a competitive | outcome or coexist. Under the more realistic situation of multiple limiting resources, we can have coexistence of multiple species of competitors when each species is limited by a different resource. |
| The outcome of competition can be altered by abiotic conditions, disturbances, and interactions with other species. | If a species is competitively superior but not tolerant of extreme abiotic conditions, it will not be able to dominate areas that experience such conditions. Similarly, competitively superior species that cannot persist with frequent disturbances, such a |
| fire, cannot come to dominate inferior competitors. In the same way, superior competitors that are more vulnerable to herbivores or predators cannot outcompete inferior competitors because they are preferentially harmed or killed. | Competition can occur through exploitation or direct interference, or it may be apparent competition. |
| Exploitative competition occurs when one species consumes enough of a resource that another species can no longer persist. In contrast, interference competition occurs when a species defends a resource and prevents other individuals from consuming it. | Interference competition includes aggressive interactions among species and allelopathy. Sometimes species appear to be competing because the presence of one species has a negative effect on the population of the other. In cases of apparent competition, |
| the underlying mechanism is not competition, but another type of interaction such as predation, herbivory, or parasitism. | Mutualisms can improve the acquisition of water, nutrients, and places to live. |
| Mutualisms can be categorized as generalists, which interact with many species, or specialists, which interact with few other species. When both species require each other to persist, they are obligate mutualists. When the interaction is beneficial but | not critical to the persistence of either species, they are facultative mutualists. Mutualisms for resources include the algae and fungi that compose lichens and the corals and zooxanthellae that build coral reefs. Plants also participate in this type of |
| mutualism by interacting with endomycorrhizal fungi, ectomycorrhizal fungi, and Rhizobium bacteria. In most animals, protists can play an important role in digesting food. Other animals construct habitats that they share with other species in exchange for | other benefits. |
| Mutualisms can aid in defense against enemies. | Plants make use of defensive mutualisms in a number of ways, including mutualisms with aggressive insects such as ants, and with endophytic fungi that produce chemicals harmful to herbivores. Animals that interact as mutualists to defend against enemies |
| include cleaner fish that remove parasites from large fish and oxpecker birds that remove ticks from mammals. | Mutualisms can facilitate pollination and seed dispersal. |
| Pollinators allow many species of plants to be fertilized and some plants have evolved traits that favor a particular type of pollinator. When this happens, the plants and the pollinators can coevolve. Numerous plants also depend on mutualisms to disperse | their seeds. In some cases, seeds are dispersed as the result of animals storing them far from the parent plant. In other cases, animals consume the fruit of plants and the seeds are dispersed after passing through their digestive systems. |
| Mutualisms can change when conditions change. | Although mutualisms benefit all species in the interaction, a positive mutualism can switch to a neutral or negative interaction when conditions change. In some cases, species can respond to cheaters in a mutualism by only rewarding individuals that |
| provide benefits in return. | Mutualisms can affect communities. |
| Mutualisms can increase or decrease the abundance of participating species. An absent mutualist can cause another species to be completely eliminated, thereby affecting the distribution of a species. Mutualists can also affect communities either by | directly altering the number of species or by initiating a chain of interactions through a community. At the ecosystem level, mutualists can also have effects such as moving nutrients into producers and increasing the total biomass of producers. |
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