Herbivory

Herbivory on oak trees is a long investigated field focusing on the high content of tannins and the corresponding adaptation of generalist and specialist insects.

From: Ecotoxicology , 2019

Herbivory

Timothy D. Schowalter , in Insect Ecology (2d Edition), 2006

Iii Summary

Herbivory, the feeding on living plant parts by animals, is a cardinal ecosystem process that has widely recognized effects on primary production and on vegetation structure and composition. The effect of herbivory depends on herbivore feeding type and intensity. Dissimilar types of herbivory affect different tissues and the production, translocation, and aggregating of photosynthates to varying degrees.

A number of methods have been used to measure the intensity and effects of herbivory. The nearly common method for measuring intensity has been estimation of consumption rates by individual herbivores and extrapolation to population size. This method can be used to measure consumption by sap-sucking herbivores as well equally folivores. A second method is measurement, by various means, of missing plant biomass. This method does non account for completely consumed (and unobserved) parts or for compensatory growth. Measurement of turnover of marked constitute parts is the most accurate, but labor-intensive, method for estimating herbivory. Estimates of herbivory tin differ by 2-5 times amid methods, making standardization a key to comparison amid ecosystems. Evaluating the effect of herbivory requires measurement of a diversity of institute and ecosystem responses, not simply institute growth or productivity.

The intensity of herbivory varies widely, but a trend is apparent among ecosystem types. Herbivory generally is lowest (<2% reduction in master production) in some forests and highest (nearly primary production consumed daily) in aquatic ecosystems. Insects are the primary herbivores in forest ecosystems and may account for the bulk of herbivory in grasslands, although vertebrate grazers are more conspicuous.

Herbivory has well-known effects on survival, productivity, and growth form of individual plants. However, the traditional view of herbivory every bit a negative effect on plants is existence replaced by a view that recognizes more complex effects of variable intensity and timing. Moderate intensities of herbivory oft stimulate production, through compensatory growth, and flowering, thereby increasing fettle. A given intensity of herbivory tin can have dissimilar furnishings at different times during the growing season or under different environmental atmospheric condition. Herbivory can bear upon the growth form of plants past terminating shoot growth and initiating branching and by affecting shoot-to-root ratios. Changes in survival, productivity, and growth of individual establish species touch on vegetation structure and customs dynamics. Herbivores often determine the geographic or habitat patterns of occurrence of establish species and facilitate successional transitions.

Few studies have addressed effects of insect herbivores on biogeochemical cycling or other abiotic conditions. However, herbivores affect, often dramatically, the turnover of plant nutrients to litter equally plant fragments, carrion and beast tissues, and nutrients leached from chewed surfaces. Folivory alters seasonal patterns of nutrient fluxes by transferring cloth prior to establish resorption of nutrients from senescing parts. Sap-sucking insects transfer copious amounts of labile carbohydrates (as honeydew) that stimulate growth and food uptake by microbes. Herbivory too may touch climate and the likelihood and intensity of future disturbances. Reducing vegetation embrace greatly affects the penetration of lite, precipitation, and wind to the understory and soil, affecting soil warming and h2o content, relative humidity, erosion, transpiration, etc. Reduced vegetation biomass or litter accumulation affects abundance of fuel to support burn down and affects water-property capacity and vegetation need for water during drought. Therefore, herbivory can influence ecosystem stability substantially (Chapter 15).

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Institute Demography

F.X. Picó , ... J. Retana , in Encyclopedia of Environmental, 2008

Herbivory

Herbivory can strongly reduce plant biomass somewhen affecting plant operation in different means (due east.g., enhancing plant growth, reducing the reproductive output, etc.) ( Figure 8 ) and almost all phases of life cycle of plants. The touch of herbivore damage on plant population dynamics depends on several factors, such every bit the kind of herbivore (e.grand., insects or vertebrates), the effect of that herbivore on a particular life-cycle stage (e.g., flowering buds or leaves), and the importance of such stage for population dynamics (east.g., reproduction vs. growth). The response of plants to herbivory at both the individual (east.k., affecting survival rates) and population level (e.g., affecting age and size structure) is also of import to determine the effects of herbivory on population dynamics. Finally, grazing-avoidance mechanisms, based on attributes external to the establish (e.g., individual plants growing in the neighborhood of spiny shrubs that protect them confronting herbivory), are also mutual in plants.

Figure 8. Shrubs grazed by domestic livestock in the Montseny Natural Park (NE Spain). The effects of herbivory are usually considered of low intensity, but herbivores tin strongly modulate plant communities in many regions of the globe. Photo courtesy of Eduard Pla.

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Arthropods and Vertebrates in Biological Control of Plants

T.S. BELLOWS , D.H. HEADRICK , in Handbook of Biological Control, 1999

Indirect Bloodshed of Plants

Herbivory can reduce existing institute biomass or crusade redirection of resource in plant tissues through many mechanisms (including defoliation, removal of constitute sap, devastation of roots, and galling of plant tissues). Such herbivory often leads to reduction in stored reserves in a plant, and reduces the charge per unit of establish growth or regrowth in the presence of herbivory. The relationship between injury from herbivores and individual plant performance (such every bit total seed set up or growth rate) is oftentimes linear ( Crawley, 1989). At moderate levels of herbivory, however, many plants are able to compensate partially or fully for losses (Trumble et al., 1993), so the relationship between the proportion of plants really dying and the corporeality of herbivorous injury may be nonlinear, and is governed by a damage threshold (Harris, 1986). This threshold is the level or amount of biomass that must exist removed before the plants cannot recoup and consequently incur an increased risk of death. Many species of forage grasses, for case, remain salubrious with annual losses to herbivory of xl% of their biomass, but when herbivory removes more than l%, grass stands decline (Harris, 1986).

Institute response to herbivory varies not only with the amount of biomass consumed or removed, only also with the flavor in which herbivory takes place. In addition, plant response will vary with the specific tissues that are attacked; particularly when the tissues attacked are also those used by the plant for storage of saccharide reserves. For plant species in which reserves are stored in foliage, defoliation is much more than likely to effect in plant death than for species in which storage occurs in other structures, such as the cambium or roots. Seasonal timing of herbivory likewise is of import in determining the event of establish-herbivore interactions. Confusion of musk thistle, Carduus thoermeri Weinmann, at the rosette stage caused bloodshed, but similar levels of defoliation subsequently development of the fruiting stalk had little effect on the plants (Cartwright & Kok, 1990).

Galling of plant tissues has its greatest consequence when tissues are attacked early in development (Harris, 1986). The institute reacts every bit if the resources used for gall formation had been used for normal tissue growth and little compensatory growth takes place. Extensive galling can act as a nutrient sink, reducing other vegetative growth and, if galling occurs in the reproductive tissues, reducing reproduction (Dennell, 1988).

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Photosynthesis, Growth Rate, and Biomass Resource allotment

Vincent P. Gutschick , in Ecology in Agronomics, 1997

F Herbivory, Pests, and Diseases Affecting Photosynthesis

Herbivory by insects and big animals during the constitute's vegetative growth stage typically has its major consequence in removing photosynthetic tissue rather than in damaging disquisitional ship pathways or removing growing points to limit recovery (Richards and Caldwell, 1985). The immediate effect of herbivory is a resetting of leaf area index and exposure of leaf area to higher solar radiation than previously encountered. Given that canopy photosynthesis (P c) saturates as LAI increases, roughly as [1-exp(− K*LAI)], a reduction of LAI at high LAI only reduces P c marginally. If K   =  0.vii and LAI   =   4, and then a 10% loss of LAI reduces P c by just 2%. This loss estimate applies well to distributed herbivory, such equally insects. Big-animal herbivory selectively removes top leaves, which leaves backside lower N leaves less acclimated to high light. Some found species and ecotypes are well adapted to such herbivory. They rapidly reallocate total stored saccharide to support regrowth (Chapin and McNaughton, 1989), and they shift the distribution of nitrogen to near-optimal patterns. Tolerant ecotypes and species must take sufficient meristems to use the reallocated resources for fast regrowth; non all do (Richards and Caldwell, 1985). Some ecotypes even have higher full productivity (though not standing biomass) with herbivory than without. However, they are most always lower in productivity than ungrazed plants with low herbivory tolerance that optimize canopy structure for total photosynthesis (Polley and Detling, 1988). In that location is pregnant confusion over definitions of "compensatory growth" in the literature. Season-integrated productivity is one practiced measure, every bit is reproductive biomass produced. Many studies leave the definition vague or implicit, and few studies involve measurement of canopy photosynthesis, either per ground area or per mass.

Continued low-level herbivory need not affect reproductive yield significantly if moderately high LAI tin can still be attained and if water is not limiting. Herbivory-tolerant ecotypes can fifty-fifty increment their fractional allocation to reproduction, especially past tillering in grasses. If water limits total biomass accumulation, then loss of photosynthetic tissue direct subtracts from total yield possible. Furthermore, plants whose aboveground biomass has been reduced by herbivory oftentimes have their competitiveness for water reduced relative to ungrazed neighbors; leaf water potentials often turn down (Senock et al., 1991).

Herbivory tolerance in photosynthetic performance need not interpret into potency or even persistence in mixed-species communities. Herbivores can evidence sufficiently strong preferences for species and so that the tolerant species becomes rarer (Brownish and Stuth, 1993).

The run a risk of herbivory is related to photosynthetic performance in that high N leaves are more bonny to many herbivores (Williams et al., 1989, and references therein). Thus, there is an evolved trade-off, which we have reset in agriculture by limiting herbivory. (The final percent loss of productivity is withal near one-third, however; Pimentel et al., 1978.) Post-obit herbivory, carbon gain is supported by remaining leaves and, subsequently a lag, by regrowth of leaf area. Newly exposed "shade" leaves have lower photosynthetic capacity (Hodgkinson et al., 1971) and may fifty-fifty lose function for awhile every bit a result of photoinhibition in the of a sudden high irradiance. If the crop canopy had been of high LAI, the rate gain of foliage mass is accelerated after herbivory, but this compensatory growth (Chapin and McNaughton, 1989) does not proceed on a fundamentally different bend of LAI vs time than that in the original crop growth.

Some pests, diseases, and parasites selectively bear upon foliage development or photosynthetic role. Others, such every bit mistletoe (Davidson et al., 1989), change plant water relations and indirectly have their greatest bear upon by reducing cumulative photosynthesis as estimated by (water available) *WUE. A third category includes stressors that impact nonphotosynthetic functions such as ship (e.g., yellowish virus of sugarbeets) and take very indirect furnishings on photosynthesis. In the showtime category of direct impact, an example is curly-pinnacle virus that both reduces leafage expansion and causes foliar chlorosis with loss of photosynthetic rate. Many leaf-spot diseases—fungal, bacterial, and viral—selectively kill areas of leaf tissue with piffling other effect, acting much similar herbivory. Yet other diseases target photosynthetic functions more than intricately (Goodman et al., 1986). The phaseola toxins attack membranes, and the mosaic viruses articulate chloroplasts. In whatever event, the course of affliction and its impact on photosynthesis and productivity is determined by the disease organism and the plant affliction-resistance physiology, not by photosynthetic acclimation responses.

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Molecules to ecosystems—recent trends in chemical ecology for combating biotic stresses in a changing climate

Chitra Shanker , ... Naganna Repelle , in Climate Change and Crop Stress, 2022

13.5.3 Impact of plant eater-induced plant volatiles on pollinators

Herbivory on various parts of plants affects pollinators in their foraging behavior. The pollinators reduce their visits to flowers that are modified past insect herbivory, thus affecting the plant's reproduction ( McCall & Irwin, 2006). HIPVs, because of herbivory, have different effects on the attraction of pollinators. The HIPVs emitted from plant eater-infested flowering plants change the pollinator behavior. The volatile emissions may heighten or deter or may not have any result on pollinators. The institute's reproduction is affected indirectly past changes in bloom chemistry. The concentration of toxins in nectar and pollen were increased past herbivory (Adler, Wink, Distl, & Lentz, 2006; McCall & Irwin, 2006) and past producing HIPVs (Kessler & Halitschke, 2009). The HIPVs released from flowers or leaves have a systemic effect on other parts of the plant (Heil & Bueno, 2007). Mechanically damaged leaves of Cucurbita pepo subsp. texana increased the volatile emissions from flowers (Theis, Kesler, & Adler, 2009). Herbivory of flowers not only induces HIPV emissions simply also reduces the emission of floral scents. Florivory by G. sexta reduced the emission of the flower volatile benzyl acetone, which attracts hawkmoths on Due north. attenuata plants (Kessler, Halitschke, & Poveda, 2011). The HIPV emission results in the attraction or repellence of members of diverse trophic levels (Dicke & Baldwin, 2010). Plants diverting their resources to emit herbivore-induced defense chemicals reduced the pollen and nectar production and therefore pollinator visitation, which impacts growth and reproduction negatively (Kessler, Halitschke, & Poveda, 2011). Many studies show that volatiles emitted due to herbivory had a negative effect on pollinators (Cardel & Koptur, 2010; Danderson & Molano-Flores, 2010; Kessler & Halitschke, 2009). Infested wild tomato plant plants feel fewer visitations by pollinators (Kessler & Halitschke, 2009). Octyl esters emitted due to florivory past parsnip webworm reduced pollination success (Zangerl & Berenbaum, 2009). Pollinator visits reduced due to combined leaf and root herbivory because of the reduced flowering period (Poveda, Steffan-Dewenter, Scheu, & Tscharntke, 2003). Uninfested wild radish plants attract bees and syrphid flies more frequently than infested plants (Lehtilä & Strauss, 1997). In contrast, pollinator visitation to mustard flowers increased through root herbivory (Poveda, Steffan-Dewenter, Scheu, & Tscharntke, 2005). There was no effect on pollinator behavior with a change in number, display, and quality of Cucurbita pepo subsp. texana flowers. But when the leaves were mechanically damaged, the pollinator visitation reduced due to volatile emissions from flowers (Theis et al., 2009). The HIPVs emitted may accept different effects on the number of pollinators or the number of visitations by pollinators to a plant. When Brassica nigra L. (Koch) was exposed to single or dual assail by herbivores on the inflorescence, the plant interactions with both pollinators and parasitoids did non change (Chrétien et al., 2021). But there was a decrease in species of pollinator community with no modify in the number of pollinator visitations (Ameye et al., 2018; Chrétien et al., 2021).

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Book 2

I.C. Barrio , D.South. Hik , in Encyclopedia of the World'southward Biomes, 2020

Future Directions

Herbivory is an active field of research in arctic ecosystems, but in that location are still many gaps. For example, we notwithstanding know relatively little about background invertebrate herbivory in tundra. Recent estimates indicate that groundwork herbivory is ubiquitous across the tundra biome and occurs at depression intensity, merely is likely to increase significantly with arctic warming ( Barrio et al., 2017). Similarly, changes in plant chemistry and how they will affect institute-herbivore interactions in a warmer future deserve further investigation. For instance, phenolic compounds are expected to subtract with increased temperature (Stark et al., 2015a,b), but the response to warming might differ depending on what type and combination of secondary metabolites plants accept (Graglia et al., 2001).

One of the main limitations in our current knowledge of chill herbivory is the large context-dependency of the results of unmarried-site studies (Bernes et al., 2015). Many factors tin attune how plants respond to herbivores, and how herbivores answer to contradistinct food availability. Existence able to generalize the results of herbivory studies in the N will allow usa generate more than robust predictions of the consequences of the rapid ongoing environmental changes in this region (Soininen et al., 2018). This is particularly true for vast and remote areas like the Arctic, where difficult admission usually implies diff sampling efforts (Metcalfe et al., 2018). Coordinated enquiry efforts and the evolution of theoretical frameworks can help move forward. For instance, the concept of functional traits and functional groups is broadly used in arctic plant ecology (Chapin et al., 1996) and has been used for invertebrate herbivores elsewhere (Deraison et al., 2015), and could be a promising approach to generalize the effects and responses of arctic herbivores. Identifying key functional traits of herbivores that mediate their impacts on arctic ecosystem structure and function, such as body size (Legagneux et al., 2014), is thus a first footstep forward.

One of the challenges when studying institute-herbivore interactions is the pattern of studies that match sampling of 2 organisms that occur potentially at different scales, and the need of long term observations to detect trajectories of alter in slowly responding tundra constitute communities (Olofsson et al., 2013). In some sites, plant eater exclusion triggers rapid changes in vegetation (Falk et al., 2015), whereas in others a fourth dimension calibration of 10   years is not enough to observe a major shift in vegetation (Gough et al., 2008). All the same, long and curt term responses can be qualitatively and quantitatively different because they tin be driven by different mechanisms and processes (Väisänen et al., 2014). Similarly, increasing or decreasing herbivore densities may not lead to the same effects on vegetation (Olofsson, 2006) and aspects like the history of grazing need to be taken into business relationship (Väisänen et al., 2014).

Dissimilar types of studies and methodologies have been used to study plant-herbivore interactions in the Chill, ranging from observational studies quantifying signs of herbivory or herbivore activity, to experimental manipulations of herbivore densities or simulated herbivory (Soininen et al., 2018). Besides, various remote-sensing techniques using satellite observations take been used to detect big-scale changes in vegetation in areas with different management (Cohen et al., 2013) or following a peak in pocket-sized mammal affluence (Olofsson et al., 2012). Harmonizing enquiry efforts volition help make more robust generalizations across sites and plant-plant eater systems (Barrio et al., 2016b). International research networks, similar the Herbivory Network (http://www.herbivory.lbhi.is) are promoting such coordinated research efforts that will ultimately amend our understanding of the office of herbivory in these systems.

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Function of Zooplankton in Aquatic Ecosystems

R.W. Sterner , in Encyclopedia of Inland Waters, 2009

Herbivory is an important procedure in planktonic ecosystems. Small-scale, rapidly growing microalgae are nutritious and often poorly defended; herbivorous zooplankton populations tin can thus develop. These can remove a relatively great fraction of master production. Feeding modes in the freshwater zooplankton include phagocytosis, filter feeding, and individual particle option. Each of these modes has different relationships between the size of the predator and the size of the prey. Zooplankton are a trophic bridge between the remainder of the ecosystem. Herbivorous zooplankton in lakes sometimes greatly reduce the abundance of planktonic algae; this occurs regularly in tardily spring in many lakes, resulting in a several-week period called a articulate water phase. It also occurs at times throughout the summertime in other habitats such as productive shallow lakes. Such loftier levels of herbivory also affect the penetration of heat and thus thermal stratification patterns. Zooplankton besides play a role in recycling nutrients into the water column; these relations have a strong stoichiometric component because zooplankton species vary in their nutrient content, which affects their food recycling patterns. The identity of an herbivore trophic level in lake ecosystems is apparent when we await at many studies involving how alterations in fish communities bear on lake ecosystems.

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Predation and Food Webs

Walter K. Dodds , Matt R. Whiles , in Freshwater Ecology (Tertiary Edition), 2020

Herbivory

Herbivory is the consumption of master producers and tin be divided into consumption of macrophytes or microscopic algae. Microscopic algae can be consumed every bit phytoplankton or as periphyton. The adaptations of organisms for consuming modest cells were discussed in Chapter 19. Herbivory can be intense, leading to algal populations that have relatively high productivity just have a total mass that is less than the mass of the animals that eat them (Vadeboncoeur and Ability, 2017).

Although invertebrates are often the chief consumers of phytoplankton, planktivorous and omnivorous fishes may ingest suspended algae (Matthews, 1998). Gizzard shad (Dorosoma cepedianum) can effectively utilize the mucus on their gill rakers to trap cells as small as 20   μm in diameter. Several species of fishes apply similar strategies to filter and retain modest particles (Sanderson et al., 1991). Some modest Tilapia (including species used in aquaculture) are also able to capture and ingest phytoplankton.

Numerous large organisms consume periphyton. The effects of grazers on benthic algae have been extensively studied and can be divided into functional and structural responses. The structural responses of periphyton to grazers include (1) a full general decrease in biomass (but not always); (ii) changes in taxonomic composition (but prediction of specific full general taxonomic shifts is difficult); (3) changes in the form and structure (physiognomy) of communities, with a general decrease in large erect forms; and (4) alteration of species richness and diversity (mayhap with intermediate levels of grazing leading to maximum diversity).

Functional responses of periphyton to grazing include (i) a general subtract in primary production per unit area, (two) constant or increasing product per unit biomass, (3) changes in nutrient content, (4) increased rate of food cycling, (5) increased rates of export of cells from the aggregation, and (half dozen) amending of successional trajectories (Steinman, 1996).

Many fishes consume periphyton and minor macrophytes (Matthews et al., 1987; Matthews, 1998). Herbivorous fishes that consume periphyton are common in tropical waters. The minnow Campostoma anomalum (cardinal stoneroller) is an important herbivorous fish in modest temperate streams in the United States. This minnow can eat significant amounts of periphyton and will be discussed later with respect to its role in nutrient webs. Many organisms swallow macrophytes in aquatic habitats, including crayfish, common carp, grass carp (Highlight twenty.1), lepidopteran and trichopteran larvae, moose (Alces alces), wild Asiatic water buffalo (Bubalis bubalis), muskrat (Ondatra zibethicus), manatees (Trichechus), ducks (Anatidae), beavers (Castor), swans (Cygnus), and snails. Many tropical fishes as well consume macrophytes (Matthews, 1998).

Highlight 20.i

Using grass carp to remove aquatic vegetation

The grass carp (Ctenopharyngodon idella) is a cyprinid that consumes aquatic vegetation every bit an adult. This herbivorous fish has been introduced into many areas to aid in removal of unwanted macrophyte growth. The fish is cultured for homo consumption in China and was beginning used in Europe to command macrophytes. It was first released in the United States in Arkansas in the early on 1960s and has since become widespread.

This species is a very effective herbivore. For example, in Texas, grass bother were stocked at 74 fish/ha in a reservoir with twoscore% macrophyte cover. All macrophytes were consumed within ane year (Maceina et al., 1992). At that place was a concurrent increase in cyanobacterial plankton and a subtract in water clarity.

There is business organisation regarding how much this species can spread, and some states have completely restricted its use for macrophyte control. The temperature range for successful reproduction is 19°C–thirty°C (Stanley et al., 1978), and considering reproduction occurs mainly in larger rivers, information technology was idea that the grass bother was unlikely to spread when added to ponds. Nonetheless, ponds take breached and reproductive fish have escaped. As a consequence, grass bother larvae have been found in the lower Missouri River, and the species has get established there (Brown and Coon, 1991). Equally the climate warms with global warming, the potential for reproduction will shift to higher latitudes.

1 approach to continue stocked fish from reproducing is to use triploid grass carp produced with thermal or temperature shocks of newly fertilized eggs. The triploids are unable to reproduce and are the only grass carp allowed in some states (Allen and Wattendorf, 1987). Scientific equipment and training are needed to decide if grass carp are really triploid. It is difficult for the average consumer or manager to know if the grass bother they purchase are truly triploid.

A problem with apply of grass carp to control macrophytes, in a direction sense, is inappropriate overstocking. Some people perceive macrophytes equally a nuisance in lakes and ponds. If many grass carp are added, all vegetation is removed. This clears the way for big algal blooms to occur in the absence of suppression past macrophytes (except see Lodge et al., 1987, for an alternative outcome). A rational arroyo is to accept a moderate corporeality of macrophytes as a healthy component of natural ponds and wetlands and control them only if they become so thick as to completely preclude desired uses such as swimming and fishing. In this case, judicious utilise of grass carp may be warranted. Sufficiently low densities should be used, so that non all macrophytes are removed. Nonfertile triploids should be stocked, so that fish volition not multiply and completely remove the macrophytes and, worse, spread to other habitats and go a nuisance. Those who use grass carp should exist aware that reduced macrophyte densities in lakes can limit recruitment of desired species such as largemouth bass, and the carp tin can cause a decrease in water clarity by increasing bioturbation and stimulating algal blooms.

Consumption rates of submerged macrophytes are loftier in freshwaters, with 40%–48% of plant biomass consumed; this is roughly v–ten times more than than in terrestrial habitats (Bakker et al., 2016). This is probably related to the fact that macrophytes are more nutrient-rich and less recalcitrant. Accordingly, herbivores tin take large impacts on ecosystems. For case, water lily leaf beetles control encompass of the floating macrophyte Nuphar lutea allowing light to reach submerged macrophytes and algae and strongly altering customs and ecosystem structure (Stenberg and Stenberg, 2012). Terrestrial grazers likewise consume emergent macrophytes. This herbivory lowers wetland plant diverseness and shapes riparian communities. Sarneel et al. (2014) suggest that this herbivory sharpens the boundary between terrestrial and aquatic habitats.

Some macrophyte species are unpalatable to herbivorous animals because they are chemically defended against consumption. In add-on, macrophytes may exist also tough for some herbivores to process (Brönmark, 1985). Macrophytes tin either synthesize or accumulate toxins (Hutchinson, 1975; Porter, 1977; Kerfoot et al., 1998). Macrophytes can be induced by grazers to produce chemical protectants. The freshwater macrophyte Cabomba caroliniana is induced to produce a chemical defence when attacked past either snail or crayfish grazers. Not only does this chemical lower feeding rates and growth rates of grazers, but these chemicals also inhibit bacteria growing on the constitute. This inhibition could protect the macrophyte from bacterial infection at the site of grazer damage (Morrison and Hay, 2011).

Some macrophytes, such as the filamentous green alga Cladophora, can be a poor food source for herbivores because they take low nitrogen and phosphorus content (Dodds and Gudder, 1992). Fertilization can increase apparent palatability of macrophytes to grazing mallard ducks. In a swimming experiment, grazing furnishings on macrophytes were greater in food-enriched treatments. However, the fertilization as well caused a shift in the macrophyte customs, so the grazing effects were interactive with competitive effects amid the plants (Bakker and Nolet, 2014).

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Predation and Food Webs

Walter K. Dodds , in Freshwater Ecology, 2002

HERBIVORY

Herbivory can be divided into consumption of macrophytes or microscopic algae. Microscopic algae can be consumed every bit phytoplankton or as periphyton. The adaptations of organisms for consuming minor cells were discussed in Affiliate 18.

Although invertebrates are the primary consumers of phytoplankton, planktivorous and omnivorous fishes may ingest suspended algae (Matthews, 1998). Gizzard shad (Dorosoma cepedianum) tin finer employ the mucus on their gill rakers to trap cells as modest as 20 μm in diameter. Several species of fish use similar strategies to filter and retain small particles (Sanderson et al., 1991). Some pocket-size Talapia are also able to capture and ingest phytoplankton.

Numerous large organisms consume periphyton. The furnishings of grazers on benthic algae take been extensively studied and tin exist divided into functional and structural responses. The structural responses of periphyton to grazers include (i) a full general decrease in biomass (but non ever); (ii) changes in taxonomic composition (only prediction of specific full general taxonomic shifts is difficult); (3) changes in the course and construction (physiognomy) of communities, with a general decrease in large erect forms; and (iv) amending of species richness and diversity (perhaps with intermediate levels of grazing leading to maximum diversity).

Functional responses of periphyton to grazing include (i) a general subtract in primary product per unit of measurement area just non per unit of measurement biomass, (2) changes in nutrient content, (iii) increased charge per unit of nutrient cycling, (four) increased rates of export of cells from the assemblage, and (v) alteration of successional trajectories (Steinman, 1996).

Many fishes swallow periphyton and minor macrophytes (Matthews et al., 1987; Matthews, 1998). Herbivorous fishes that consume periphyton are common in tropical waters. The minnow Campostoma anomalum (the central stoneroller) is an important herbivorous fish in small streams in the Us. This minnow tin consume significant amounts of periphyton and volition be discussed afterward with respect to its role in food webs.

Many organisms consume macrophytes in aquatic habitats, including crayfish, common carp, grass carp (Sidebar 19.i), lepi-dopteran and trichopteran larvae, moose, and snails. Many tropical fishes consume macrophytes (Matthews, 1998).

Sidebar xix.i

Using Grass Carp to Remove Aquatic Vegetation

The grass bother (Ctenopharyngodon idella) is a cyprinid that consumes aquatic vegetation equally an adult. This herbivorous fish has been introduced into many areas to assist in removal of unwanted macrophyte growth. Information technology was first released in the United states of america in Arkansas in the early 1960s and has since become widespread.

This species is a very effective herbivore. For instance, in Texas grass carp were stocked at 74 fish per hectare in a reservoir with 40% macrophyte cover. All macrophytes were consumed within ane year (Maceina et al., 1992). There was a concurrent increase in cyanobac-terial plankton and a decrease in water clarity.

In that location is business regarding how much this species tin can spread, and some states have completely restricted its utilise for macrophyte control. The temperature range for successful reproduction is xix–xxx°C (Stanley et al., 1978), and considering reproduction occurs mainly in larger rivers, it was thought that the grass carp was unlikely to spread when added to ponds. However, ponds take breached and reproductive fish take escaped. As a outcome, grass carp larvae have been institute in the lower Missouri River, and the species has likely become established there (Brown and Coon, 1991).

One arroyo to proceed stocked fish from reproducing is to use triploid grass carp produced with thermal or temperature shocks of newly fertilized eggs. The triploids are unable to reproduce and are the only grass carp immune in some states (Allen and Wattendorf, 1987). Scientific equipment and preparation are needed to determine if grass carp are actually triploid.

A trouble with use of grass carp to command macrophytes, in a management sense, is inappropriate overstocking. Some people perceive macrophytes as a nuisance in lakes and ponds. If many grass carp are added, all vegetation is removed. This clears the mode for big algal blooms to occur in the absence of suppression past macrophytes (except come across Gild et al., 1987, for an alternative outcome). A rational arroyo is to accept a moderate amount of macrophytes as a healthy component of natural ponds and wetlands and command them simply if they become so thick as to completely preclude desired uses. In this example, judicious use of grass bother may be warranted. Sufficiently low densities should exist used so that not all macrophytes are removed. Nonfertile triploids should be stocked and so that fish will non multiply and completely remove the macrophytes and, worse, spread to other habitats and get a nuisance.

Some macrophyte species are unpalatable to herbivorous animals considering they are chemically defended against consumption. Macrophytes tin can either synthesize or accrue toxins (Hutchinson, 1975; Porter, 1977; Kerfoot et al., 1998) and may be too tough for some herbivores to procedure (Brönmark, 1985). Some macrophytes, such equally the filamentous green alga Cladophora, can exist a poor nutrient source to herbivores because they have depression nitrogen and phosphorus content (Dodds and Gudder, 1992).

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Predation and Food Webs

Walter K. Dodds , Matt R. Whiles , in Freshwater Environmental (Second Edition), 2010

Herbivory

Herbivory can exist divided into consumption of macrophytes or microscopic algae. Microscopic algae can be consumed every bit phytoplankton or as periphyton. The adaptations of organisms for consuming small cells were discussed in Chapter nineteen.

Although invertebrates are the primary consumers of phytoplankton, planktivorous and omnivorous fishes may ingest suspended algae (Matthews, 1998). Gizzard shad (Dorosoma cepedianum) tin effectively use the fungus on their gill rakers to trap cells as modest as 20   μm in bore. Several species of fish utilise similar strategies to filter and retain small particles (Sanderson et al., 1991). Some pocket-sized Tilapia (including species used in aquaculture) are too able to capture and ingest phytoplankton.

Numerous big organisms consume periphyton. The effects of grazers on benthic algae have been extensively studied and can be divided into functional and structural responses. The structural responses of periphyton to grazers include (1) a full general decrease in biomass (but not e'er); (2) changes in taxonomic composition (but prediction of specific general taxonomic shifts is hard); (three) changes in the form and structure (physiognomy) of communities, with a full general decrease in big cock forms; and (4) alteration of species richness and diversity (perchance with intermediate levels of grazing leading to maximum diversity).

Functional responses of periphyton to grazing include (1) a full general decrease in master product per unit area, (2) constant or increasing product per unit of measurement biomass, (iii) changes in food content, (4) increased rate of nutrient cycling, (v) increased rates of export of cells from the assemblage, and (half-dozen) alteration of successional trajectories (Steinman, 1996).

Many fishes swallow periphyton and small macrophytes (Matthews et al., 1987; Matthews, 1998). Herbivorous fishes that consume periphyton are common in tropical waters. The minnow Campostoma anomalum (the cardinal stoneroller) is an of import herbivorous fish in pocket-sized streams in the U.s.a.. This minnow can swallow pregnant amounts of periphyton and will be discussed later with respect to its part in nutrient webs. Many organisms consume macrophytes in aquatic habitats, including crayfish, common carp, grass carp (Sidebar twenty.1), lepidopteran and trichopteran larvae, moose (Alces alces), wild Asiatic water buffalo (Bubalis bubalis), muskrat (Ondatra zibethicus), manatees (Trichechus), ducks (Anatidae), beavers (Castor canadensis), swans (Cygnus), and snails. Many tropical fishes likewise consume macrophytes (Matthews, 1998).

Sidebar 20.1

Using Grass Carp to Remove Aquatic Vegetation

The grass carp (Ctenopharyngodon idella) is a cyprinid that consumes aquatic vegetation as an adult. This herbivorous fish has been introduced into many areas to assistance in removal of unwanted macrophyte growth. It was first released in the United States in Arkansas in the early on 1960s and has since get widespread.

This species is a very constructive herbivore. For example, in Texas, grass carp were stocked at 74 fish per hectare in a reservoir with xl% macrophyte cover. All macrophytes were consumed within ane year (Maceina et al., 1992). There was a concurrent increase in cyanobacterial plankton and a decrease in water clarity.

At that place is concern regarding how much this species tin spread, and some states accept completely restricted its apply for macrophyte control. The temperature range for successful reproduction is 19 to xxx°C (Stanley et al., 1978), and because reproduction occurs mainly in larger rivers, it was thought that the grass carp was unlikely to spread when added to ponds. However, ponds have breached and reproductive fish have escaped. Equally a result, grass carp larvae take been found in the lower Missouri River, and the species has likely become established in that location (Brown and Coon, 1991).

One arroyo to keep stocked fish from reproducing is to utilize triploid grass carp produced with thermal or temperature shocks of newly fertilized eggs. The triploids are unable to reproduce and are the just grass bother allowed in some states (Allen and Wattendorf, 1987). Scientific equipment and training are needed to determine if grass carp are actually triploid.

A trouble with employ of grass bother to control macrophytes, in a management sense, is inappropriate overstocking. Some people perceive macrophytes as a nuisance in lakes and ponds. If many grass carp are added, all vegetation is removed. This clears the way for large algal blooms to occur in the absenteeism of suppression by macrophytes (except come across Lodge et al., 1987, for an culling outcome). A rational approach is to accept a moderate amount of macrophytes as a healthy component of natural ponds and wetlands and control them but if they become so thick as to completely forbid desired uses such as swimming and fishing. In this case, judicious use of grass carp may be warranted. Sufficiently low densities should be used so that not all macrophytes are removed. Nonfertile triploids should be stocked so that fish will non multiply and completely remove the macrophytes and, worse, spread to other habitats and become a nuisance. Those who use grass carp should be aware that reduced macrophyte densities in lakes can limit recruitment of desired species such every bit largemouth bass, and the carp can crusade a decrease in water clarity by increasing bioturbation and stimulating algal blooms.

Some macrophyte species are unpalatable to herbivorous animals because they are chemically defended against consumption. Macrophytes can either synthesize or accumulate toxins (Hutchinson, 1975; Porter, 1977; Kerfoot et al., 1998) and may be also tough for some herbivores to process (Brönmark, 1985). Some macrophytes, such equally the filamentous greenish alga Cladophora, can be a poor nutrient source for herbivores because they accept low nitrogen and phosphorus content (Dodds and Gudder, 1992).

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