Diet of free-range herbivores

Diet of free-range herbivores

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Giving minimal credence to estimates in popular media of the average biomass of insects/arachnids, etc. in an acre of land, it seems that a "free-range" cow (I don't mean to pick on cows) might be something of an omnivore. Is there any evidence that herbivores derive essential parts of their diet from sources other than cellulose? Or that they do not?

One key nutrient worth thinking about in the context of this question is vitamin B12. Herbivores such as cows and sheep will derive this directly from the bacteria in their rumen. Rabbits produce two types of feces - soft and hard - and they eat the soft variety, rich in gut bacteria, as a source of nutrients like vitamin B12. Gorillas are primarily herbivores, but are thought to derive their vitamin B12 from insects, eaten purposefully or inadvertently.

So yes, herbivores derive this particular nutrient from non-plant sources.

The global distribution of diet breadth in insect herbivores

Dietary specialization determines an organism’s resource base as well as impacts on host or prey species. There are important basic and applied reasons to ask why some animals have narrow diets and others are more generalized, and if different regions of the Earth support more specialized interactions. We investigated site-specific host records for more than 7,500 species of insect herbivores. Although host specialists predominate, the proportion of specialists is affected by the diversity of hosts and shifts globally, supporting predictions of more exclusive tropical interactions. These results not only affect our understanding of the ecology of food webs, but also have implications for how they respond to environmental change, as well as for ecosystem management and restoration.

Graphical abstract

Plant-insect interactions are dynamic and represent over 400 million years of co-evolutionary history (Despres et al., 2007, Ehrlich and Raven, 1964). These interactions have resulted in the development of sophisticated defence machinery in plants to reduce herbivory and disarming mechanisms in herbivores to offset these plant defences (Baldwin, 2001, Despres et al., 2007). Adaptive traits that have accumulated in plants and insect herbivores over generations lead to phylogenetic diversification and co-evolution (Chown and Terblanche, 2006, Futuyma and Agrawal, 2009, Thompson, 1994). In herbivorous insects, host selection appears to be tightly linked to evolutionary radiation (Janz et al., 2006) and they frequently exhibit rapid host shifts, sometimes including large-scale oscillations in the specificity of whole clades (Nylin et al., 2014). This makes them excellent models for study of mechanisms of ecological adaptation and speciation. Furthermore, from an applied perspective, the same properties also facilitate the steady emergence of new insect pests among our agro-ecosystems.

Herbivorous insects typically have a narrow range of host plants, with 80–90% considered to be more specialised, whereas only 10–20% are generalists (Schoonhoven et al., 2005). One important determinant of host specificity, in addition to neural, behavioural, and ecological factors, is the physiological limitation in overcoming plant defences (Pauchet et al., 2010). The ability to detoxify or metabolize plant allelochemicals inside the gut is one of the essential mechanisms insects have evolved for managing the diversity of phytotoxins in their diet (Berenbaum, 2002, Karasov et al., 2011).

Specialist herbivores mostly rely on effective sequestering or detoxification mechanisms to counter or manipulate host plant defence chemistry (Engler et al., 2000, Ratzka et al., 2002, Sasabe et al., 2004). Contrary to detoxification strategies that rely on degradation and excretion, sequestration results in utilization of plant toxins by specialist insects for their own benefit (Engler et al., 2000, Ratzka et al., 2002, Sasabe et al., 2004). Generalists, on the other hand, must be able to detoxify plant allelochemicals by chemical modification, degradation, and excretion, to handle a wide range of diverse plant toxins to accommodate their wider diet breadth (Badenes-Perez et al., 2013, Dussourd, 1999, Francis et al., 2005). Thus, polyphagy demands sophisticated adaptations in order to handle a broad assortment of challenges that come with processing a varied diet. An important factor would be the presence of genetic adaptations that allow the induction of arrays of broader or more robustly active digestive and protective proteins in generalist species (Janz and Nylin, 2008, Ragland et al., 2015). The underlying molecular mechanisms that allow generalist insect herbivores to circumvent both nutritional deficit and diverse chemical defence are still poorly understood. It is assumed that a broad range of detoxifying enzymes are utilized, such as glutathione transferases [GSTs], UDP-glucosyl transferases [UGTs], cytochrome P450 monooxygenases [P450s] and carboxylesterases [CEs], which potentially aid plasticity in host choice (Bues et al., 2005, Halon et al., 2015, Johnson, 1999, Schuler, 2011, Sonoda and Tsumuki, 2005).

Although “Omics” technologies, including next generation sequencing, have been significantly developed over the last decade, studies on the global transcriptomic responses in the gut of herbivores to host plant defence chemistry are until very recently few in number (Celorio-Mancera et al., 2013, Dermauw et al., 2013, Etges et al., 2015, Govind et al., 2010, Herde and Howe, 2014, Hoang et al., 2015, Ragland et al., 2015, Wybouw et al., 2015). In the present study, we try to provide a comprehensive insight into the mechanisms of host plant adaptation in generalist herbivores through an RNA-Seq approach, which is a powerful tool for differential gene expression analysis with high resolution and low background noise (Garber et al., 2011, Li and Dewey, 2011, Wilhelm and Landry, 2009).

In general, examination of closely related species pairs have been suggested for evolutionary comparisons of different degrees of polyphagy as well as for specialist/generalist comparisons (Ali and Agrawal, 2012). Closely related taxa are ideal as they share a common genetic background, with biological differences mainly in their feeding ecology, thus avoiding the “phylogenetic noise” present when comparing phylogenetically distant taxa that have accumulated more diverse adaptations. The genus Spodoptera contains mostly generalist species (Kergoat et al., 2012). The old world (Europe, Asia, and Africa) species Spodoptera littoralis (Boisduval) shows a very broad host range including mostly dicot, but also monocot plants and shows a very high behavioural plasticity in host plant choice (Proffit et al., 2015, Thöming et al., 2013). The new world (North and South America) species Spodoptera frugiperda (J.E. Smith), together with 7 other species, comprise a clade as one of three independent specialisation events towards monocots within the genus (Kergoat et al., 2012). It mainly feeds on monocot plants and shows a preference for grasses and grains, but can also thrive on some dicots (Glauser et al., 2011, Groot et al., 2010). The difference in host plant range within the Spodoptera genus provides an opportunity for studies on adaptations to host plants. Here we have an ideal set of three taxa available within a single genus that are diverse in feeding ecology: a broad generalist species S. littoralis (SL) and two strains of a less polyphagous species S. frugiperda (Corn strain, SF-C) and S. frugiperda (Rice strain, SF-R).

Maize (Zea mays) is a C4 plant with tough tissue and low nitrogen content (Barbehenn et al., 2004, Mattson, 1980). Moreover, in monocotyledonous plants such as maize, the main defence compound, a benzoxazinoid referred to as DIMBOA, serves as a natural defence and anti-feedant against a wide range of herbivorous insect pests, pathogenic fungi and bacteria (Ahmad et al., 2011, Macías et al., 2009, Niemeyer, 2009). It was recently reported that maize could also activate lipid oxidation pathways as a defence signal against mechanical damage or herbivory (Christensen et al., 2013). Hence, having a different morphology, nutritional content, and secondary chemistry compared to an artificial diet, maize is assumed to induce diverse defence responses within and among these closely related generalist herbivores enabling us to compare their taxon-specific defence strategies.

In this comparative study, we address two main questions: 1) Do the three Spodoptera taxa display divergent fitness-relevant responses during feeding? Will the broad generalist perform as well on a monocot as the grass adapted species? 2) Is midgut expression of genes related to feeding metabolism more drastically regulated in the broad generalist confronted with a monocot plant, compared to the reaction-norm of the grass-adapted generalists? Will the two grass-adapted taxa show the same expression patterns?

To address these questions, we compared the Spodoptera taxa when reared on either a semi-artificial pinto bean diet or detached young maize leaves, by analysing their feeding performance and midgut RNA-Seq expression profiles. We first examined the differences in the broad generalist, S. littoralis, in response to pinto diet (optimal for growth) versus the suboptimal host plant maize. Secondly, we compared the reaction-norm of the broad generalist, S. littoralis, to each of the two host strains of grass adapted S. frugiperda on pinto diet versus maize. Our findings reveal similar reaction-norms of fitness-relevant differences in feeding performance and of the corresponding differences at the gut transcriptome level within and across insect taxa. Amongst these polyphagous herbivores, our data indicates a broader diet dependent response of midgut physiology in the more generalist (SL), while the two S. frugiperda strains (SF-C and SF-R) showed an unexpected expression differences on the same diet.


An herbivore is an organism that eats mainly plants and other producers.

Biology, Ecology, Conservation

Panda Cubs on Treetop

Herbivores are primary consumers, meaning they eat producers, such as plants and algae. Giant pandas (Ailuropoda melanoleuca), like these cubs at the Wolong Natural Reserve in China, are herbivores.

An herbivore is an animal that mainly eats plants. Herbivores vary in size from small, like bugs, to large, like giraffes.

An animal&rsquos diet determines where it falls on the food chain, a sequence of organisms that provide energy and nutrients for other organisms. Each food chain consists of several trophic levels, which describe an organism&rsquos role in energy transfer in an ecosystem. Herbivores are primary consumers, which means they occupy the second trophic level and eat producers.

For each trophic level, only about 10 percent of energy passes from one level to the next. This is called the 10 percent rule. Because of this rule, herbivores only absorb around 10 percent of the energy stored by the plants they eat.

Not all herbivores eat the same, however. While some herbivores consume a wide variety of plants, others consume specific plant parts or types. For example, frugivores eat fruit, granivores eat seeds, folivores eat leaves, and nectarivores eat nectar.

Herbivores have various physical features evolved specifically for their diet as well. Many herbivores have large, flat molars for grinding tough plant matter. Additionally, herbivores often have multiple stomach chambers and a specialized digestive system. For example, cows have a stomach with four chambers. The food a cow consumes first passes through two stomach chambers before returning to the mouth for additional chewing. This returned food is called cud. Once the cow rechews and swallows the cud, it passes through the third and fourth stomach chambers for further digestion.

Herbivores play an important role in maintaining a healthy ecosystem by preventing an overgrowth of vegetation. Additionally, many plants rely on herbivores such as bees to help them reproduce. By the same token, herbivores rely on plants not just for food but also for habitats and shelter.

Herbivores also serve as a food source for meat eating carnivores, which keeps plant eaters from overpopulating and overgrazing an ecosystem. For example, in 1995, wolves were reintroduced into Yellowstone National Park to control the elk population. Through their overgrazing, the elk had damaged trees, increased erosion, and spoiled trout streams. In the following years, the wolves helped stabilize the elk population and restored balance to the Yellowstone ecosystem.

Insectivore Mammals

Arthropods make up almost the entire diet of most insectivore mammals such as shrews, the Microchiropterine bats, pangolins, anteaters, aardvarks and aardwolves. They also make a considerable contribution to the diets of moles, foxes, badgers, mongooses, skunks as well as many primates and rodents.

Mole (Talpa europaea) is primarily insectivorous

The diets of many insectivores are often quite varied. One study of the European Mole showed that of 200 moles analysed after death:

  • 178 had been recently feeding on earthworms,
  • 130 on beetle larvae,
  • 74 on adult beetles,
  • 70 on flies,
  • 35 on moths and butterflies,
  • 18 on bees, wasps and ants,
  • 52 on millipedes and centipedes,
  • 10 on slugs and snails,
  • 3 on mice,
  • 19 on moles and
  • 17 on plants.

Obviously, most moles feed on a variety of substances each day, taking advantage of whatever is available.

Humans actually have adapted to be able to eat both meat and plants, turning us into omnivores, even though our bodies are much more similar to herbivores. Now, in the wild, this would mean that we would eat mostly plant matter and would eat a very small amount of meat matter. In today's society, this is completely flip-flopped in the other direction.

Most people eat mostly meat products. You may think I am exaggerating, but think of all the milk, eggs, and meat that you actually eat. Usually it's a breakfast, lunch, dinner, dessert, and snack thing. We eat tons of it without even realizing it. And, we don't eat nearly enough plant matter.

Because humans are herbivores, our bodies simply crave more of the plant matter. Without it we develop diseases and die at younger ages. 


On the consistent diet, TFN was 1·99 ± 0·26% OM (mean ± SD), MFN was 1·61 ± 0·23% OM, and FNDF was 54·1 ± 4·8% DM in ruminants and 1·51 ± 0·27% OM, 1·17 ± 0·23% OM and 66·2 ± 5·1% DM in hindgut fermenters, respectively (Table 1, Fig 2). A significant effect of BM was not found for TFN or MFN (PGLS: P = 0·531 and P = 0·466 Table 2). In contrast, digestion type generally had an effect on both TFN (P = 0·004) and MFN (P = 0·003), indicating a higher digestive ability in ruminants similarly, FNDF was lower in ruminants (Steuer et al. 2013 ). Notably, 24 h gas production, the proxy for diet quality of the different parts of the grass hay batch used in the trial, never had a significant effect on the results (Table 2).

Dependent Independent OLS PGLS
Variables Variables F P R 2 t P R 2
TFN BM 0·450 0·514 0·49 0·64 0·531 0·47
DT 11·958 0·004 3·40 0·004
24 h GP 0·000 0·987 0·00 1·00
MFN BM 0·604 0·451 0·52 0·75 0·466 0·51
DT 13·470 0·003 3·62 0·003
24 h GP 0·005 0·942 0·00 1·00
FNDFa a Data from Steuer et al. ( 2013 ).
BM 1·909 0·190 0·68 1·29 0·221 0·65
DT 26·500 <0·001 4·93 <0·001
24 h GP 0·006 0·941 0·19 0·850
  • TFN, total faecal nitrogen MFN, metabolic faecal nitrogen FNDF, faecal neutral-detergent fibre BM, body mass DT, digestion type (ruminant foregut fermenter or hindgut fermenter) 24-h GP, gas production of hay in Hohenheim gas test (24 h) OLS, ordinary least squares PGLS, phylogenetic generalized least squares.
  • a Data from Steuer et al. ( 2013 ).

In free-ranging animals, TFN ranged from 1·68% OM (hartebeest) to 3·78% OM (gerenuk) in ruminants and from 1·05% OM (elephant) to 1·82% OM (warthog) in hindgut fermenters (Table 3). In the GLM, BM and DT both had a significant effect on TFN, while% grass only had an influence in the OLS data set (Table 4). MFN ranged from 0·79% OM (giraffe) to 1·85% OM (Grant's gazelle) in ruminants and 0·46% OM (black rhino) to 1·06% OM (warthog) in hindgut fermenters (Table 3 Fig 2). In the GLM, both BM and DT had an influence on MFN values, while% grass did not (Table 4). FNDF values ranged from 36·4% DM (hartebeest) to 67·9% DM (giraffe) in ruminants and from 59·2% DM (warthog) to 79·8% DM (black rhinoceros) in hindgut fermenters (Table 3). BM, DT and % grass all had significant effects on FNDF (Table 4).

Kg % OM % OM % DM % in diet
Tragelaphus spekii 3 80 2·96 1·30 58·4 92·1
Alcelaphus buselaphus 1 130 1·68 1·31 36·4 93·4
Oryx beisa 10 170 1·77 1·37 39·8 92·8
Kobus ellipsiprymnus 8 215 2·06 1·18 46·3 86·7
Syncerus caffer 10 630 2·05 1·23 59·7 89·3
Aepyceros melampus 10 50 2·77 1·65 50·6 38·9
Oreotragus oreotragus 9 12 2·81 1·29 42·9 19·0
Lithocranius walleri 4 40 3·78 1·76 53·4 13·8
Tragelaphus scriptus 12 60 2·65 1·58 44·8 0·0
Nanger granti 13 65 2·99 1·85 41·9 19·5
Tragelaphus strepsiceros 10 200 2·29 1·09 61·3 13·0
Taurotragus oryx 12 500 2·12 1·13 58·8 7·3
Giraffa camelopardalis 9 850 2·87 0·79 67·9 8·9
Phacochoerus africanus 11 73 1·82 1·06 59·2 94·8
Equus quagga 12 230 1·19 0·71 64·1 97·0
Equus grevyi 11 410 1·35 0·89 64·0 100·0
Ceratotherium simum 10 1900 1·12 0·68 65·3 95·8
Diceros bicornis 10 1000 1·19 0·46 79·8 11·4
Loxodonta africana 11 4000 1·05 0·48 79·7 33·6
Dependent Independent OLS PGLS
Variables Variables F P R 2 t P R 2
TFN BM 8·09 0·012 0·76 2·56 0·022 0·72
DT 8·55 0·010 3·04 0·008
% grass 4·51 0·051 1·62 0·127
MFN BM 14·2 0·002 0·78 3·78 0·002 0·77
DT 10·3 0·006 3·15 0·007
% grass 0·143 0·711 0·380 0·706
FNDF BM 11·9 0·004 0·76 3·42 0·004 0·76
DT 11·5 0·004 3·33 0·005
% grass 6·17 0·025 2·42 0·028
  • TFN, total faecal nitrogen MFN, metabolic faecal nitrogen FNDF, faecal neutral-detergent fibre BM, body mass DT, digestion type (ruminant foregut fermenter or hindgut fermenter) OLS, ordinary least squares PGLS, phylogenetic generalized least squares.

Allometric regressions for data of free-ranging animals (all PGLS) were

  • TFN = 2·9 (95% CI: 1·6 5·4) * BM −0·09 (95% CI: −0·17 −0·01) P = 0·054, R 2 = 0·20,
  • MFN = 2·3 (95% CI: 1·4 4·1) * BM −0·15 (95% CI: −0·23 −0·07) P = 0·004, R 2 = 0·40, and
  • FNDF = 36·3 (95% CI: 26·3 50·1) * BM 0·08 (95% CI: 0·02 0·14) P = 0·014, R 2 = 0·31.

Relationships between the variables are presented in the Supplement. Notably, FNDF did not significantly relate to TFN, but to MFN, in general linear models, emphasizing that variability in TFN most likely introduced by dietary tannins is less when using MFN as digestibility proxy.

"Pharm-ecology" of diet shifting: biotransformation of plant secondary compounds in creosote (Larrea tridentata) by a woodrat herbivore, Neotoma lepida

Diet switching in mammalian herbivores may necessitate a change in the biotransformation enzymes used to process plant secondary compounds (PSCs). We investigated differences in the biotransformation system in the mammalian herbivore, Neotoma lepida, after a radical shift in diet and secondary compound composition. Populations of N. lepida in the Mojave Desert have evolved over the past 10,000 years to feed on creosote (Larrea tridentata) from an ancestral state of consuming juniper (Juniperus osteosperma). This dietary shift represents a marked change in the dietary composition of PSCs in that creosote leaves are coated with phenolic resin, whereas juniper is high in terpenes but lacks phenolic resin. We quantified the enzyme activity of five major groups of biotransformation enzymes (cytochrome P450s, NAD(P)H:quinone oxidoreductase, glutathione conjugation, sulfation, and glucuronidation) recognized for their importance to mammalian biotransformation for the elimination of foreign compounds. Enzyme activities were compared between populations of Mojave and Great Basin woodrats fed control and creosote diets. In response to creosote, the Mojave population had greater levels of cytochrome P450s (CYP2B, CYP1A) and glutathione conjugation liver enzymes compared with the Great Basin population. Our results suggest that elevated levels of cytochrome P450s and glutathione conjugation enzymes in the Mojave population may be the underlying biotransformation mechanisms that facilitate feeding on creosote.

Advantages and Disadvantages of Being an Herbivore

Plants such as phytoplankton are relatively abundant in ocean areas with access to sunlight, such as in shallow waters, at the surface of the open ocean, and along the coast. An advantage of being an herbivore is that food is pretty easy to find and eat. Once it is found, it can't escape like a live animal might.

One of the disadvantages of being an herbivore is that plants are often more difficult to digest than animals. More plants may be needed to provide adequate energy for the herbivore.

Chlorogenic acid-mediated chemical defence of plants against insect herbivores

J. Vadassery, National Institute of Plant Genome Research (NIPGR), Aruna Asaf Ali Marg, P.O. Box 10531, New Delhi 110067, India.

National Institute of Plant Genome Research (NIPGR), New Delhi, India

National Institute of Plant Genome Research (NIPGR), New Delhi, India

J. Vadassery, National Institute of Plant Genome Research (NIPGR), Aruna Asaf Ali Marg, P.O. Box 10531, New Delhi 110067, India.


Chlorogenic acid is one of the most abundant beneficial polyphenols in plants and is well known as a nutritional antioxidant in plant-based foods. Apart from its dietary antioxidant activity, it has been proved to be an efficient defence molecule against a broad range of insect herbivores. In the last two decades, several reports have shown the effectiveness of chlorogenic acid in insect growth deterrence. The pathway for chlorogenic acid biosynthesis in plants was previously elucidated, and metabolic engineering of the principal pathway showed high chlorogenic acid production in tomato plants. Herbivore-mediated induction of chlorogenic acid biosynthesis was also demonstrated both at metabolite and transcript level, although herbivore-mediated molecular regulation of chlorogenic acid biosynthesis is not yet fully elucidated. In this communication, we present our views on the efficacy of chlorogenic acid as an anti-herbivore defence molecule in plants and also discuss its future outlook.

Watch the video: Γιατί το πρωινό είναι το βασικότερο γεύμα για μια υγιεινή διατροφή. (February 2023).