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Animal populations must be able to acquire an adequate amount of nutrients to persist regardless of what environment they are in. In highly variable environments, such as drylands where food sources are limited, this potential mismatch between physiological demands and what is available in the environment is accentuated. For herbivores, the balance of macronutrients (protein and carbohydrate) is particularly important and both nutrients are highly variable in plants both spatially and temporally. Whereas it is known that many herbivores will forage multiple plants to achieve an optimal nutritional ratio (termed the intake target), it is less known how herbivores with different life history strategies address this in variable environments. In this study, we measured the intake targets of three grasshopper species with differing life history strategies, two migratory and one non‐migratory, at three locations in New South Wales, Australia. We measured nutrient variation in plants spatially and temporally by sampling three different locations and repeated the measurement twice for one of these locations. At all three locations and both times, host plant protein differed substantially but carbohydrate content remained constant. The non‐migratory grasshopper species shifted their intake target, presumably to redress nutrient imbalances. On the other hand, the two migratory grasshopper species largely maintained the same intake target, even when in a nutritionally suboptimal environment. These results suggest that non‐migratory species are likely more limited in their capacity to forage for optimal diets and may rely more on digestion to survive in nutritionally suboptimal locations. In contrast, migratory grasshoppers may migrate to obtain the nutrients they need instead of redressing imbalances locally. Therefore, a strong metapopulation structure may aid in the persistence of migratory species at larger spatial scales. Since herbivores, especially insects, are important from nutrient cycling to food chains, understanding how populations persist in nutritionally variable environments is important to the overall ecosystem functioning. Further research should consider how nutritional demands drive population dynamics and how it changes with life history strategies.

There is generally a close relationship between a consumer's food and its optimal nutrients. When there is a mismatch, it is hypothesized that mobile herbivores switch between food items to balance nutrients, however, there are limited data for field populations. In this study, we measured ambient plant nutrient content at two time points and contrasted our results with the nutrient ratio selected by wild female and male grasshoppers (Oedaleus senegalensis). Few plants were near O. senegalensis’ optimal protein:carbohydrate ratio (P:C), nor were plants complementary. Grasshoppers collected earlier all regulated for a carbohydrate-biased ratio but females ate slightly more protein. We hypothesized that the long migration undertaken by this species may explain its carbohydrate needs. In contrast to most laboratory studies, grasshoppers collected later did not tightly regulate their P:C. These results suggest that field populations are not shifting their P:C to match seasonal plant nutrient shifts and that mobile herbivores rely on post-ingestive mechanisms in the face of environmental variation. Because this is among the first studies to examine the relationship between ambient nutrient landscape and physiological state our data are a key step in bridging knowledge acquired from lab studies to hypotheses regarding the role ecological factors play in foraging strategies.

Terrestrial molluscs are some of the most important herbivores in temperate habitats. They tend to be generalists and can be serious pests in agricultural fields, particularly no-till fields used for field and forage crops; however, farmers have access to few commercially available solutions, and the existing ones present many disadvantages (e.g. reliability, cost, environmental concerns). In this paper, we review these current management options with a focus on agronomic crops, as well as the biotic factors that influence mollusc feeding, such as natural enemies, plant nutritional content, and chemical defences. These biotic factors all have important direct consequences on mollusc fitness and can be manipulated in agricultural settings. We then review evidence from the latest research in the field of nutritional ecology to propose the use of the Geometric Framework, a well-established nutritional approach, to measure nutrient regulation and performance of terrestrial molluscs and develop ecologically based management programs that also relies on susceptibility to natural enemies. To illustrate our point, we detail a specific strategy being used by farmers in the Mid-Atlantic US to manage slug populations; in this system, farmers are using cover crops terminated after the cash crop is planted (also called “planting green”) and this approach appears to harness slug nutritional preferences and natural enemies to manage slug populations.

Agriculture is a major factor in landscape fragmentation, altering nutrient cycling and animal and plant populations through increasing habitat edge density. Most research on insect herbivores in agroecosystems has focused on the top-down effects of predators moving throughout the habitat mosaic. Few studies have focused on the top-down and bottom-up factors modulating the distribution of insect herbivore populations between natural and agricultural patches. For example, despite an understanding that Australian plague locusts (Chortoicetes terminifera) avoid tree patches, the underlying mechanisms remain unknown. Here, we explored how wooded remnants within pastures affect locust density and the potential top-down and bottom-up mechanistic explanations. We tested three hypotheses: 1) grasses near wooded areas are nutritionally suboptimal, 2) predator density is higher near wooded areas, and 3) temperatures are cooler underneath trees. We measured locust density, grass nutrient content, predator abundance, temperature, and ground cover along 50 m transects from wooded areas to open grassy areas. We ran those transects in three fields and had four transects per field. We confirmed locust avoidance for trees at a 20 m periphery, however none of the variables tested independently explained this trend. Grass nutrient content was similar underneath wooded areas and in open patches. Predator abundance did not differ between the two habitats. The ground was warmer under wooded areas than in grassy areas potentially due to woody vegetation negating windchill. Further, we found that locust density was negatively correlated with plant protein content and was highest in areas with approximately 20 % bare ground cover. Both plant protein and ground cover are important for grasshopper performance and reproduction. It is likely a complex interaction between these variables and others that drive the distribution of this species and other insect herbivores in agroecosystems. The small-scale mechanisms driving the response of insect herbivores to landscape changes is critical to understanding and predicting population dynamics at large-scales.

International audience; 18 Cropland cultivated under no-tillage has dramatically increased in Brazil during the last three 19 decades. However, soil degradation by water erosion remains excessive in the country. 20 Furthermore, the impact of inappropriate agricultural practices on soil erosion is often neglected 21 by farmers. Therefore, the contribution of potential sources of sediment should be quantified in 22 order to raise awareness among rural communities on the need to improve land management for 23 protecting soil and water resources. This study quantified the contribution of potential sources to 24 sediment transiting the Guaporé River, draining a 2032-km² cultivated catchment, in Southern 25 Brazil. Potential sediment source types were surface of cropland soils (n = 159), unpaved roads 26 (n = 58), and stream channel banks (n = 46). A total of 175 suspended sediment samples were 27 collected following different sampling strategies (including sampling of river water during 28 floods, installation of time-integrated suspended sediment samplers, and collection of bed 29 sediment) in 10 sub-catchments, from January 2011 to March 2014. Discriminant properties 30 were selected among the concentrations in 22 geochemical elements and total organic carbon. 31 Results showed that sediment source contributions were similar for the different sediment 32 sampling strategies. Although, the contributions of sediment sources varied in space across 33 Guaporé catchment, they were dominated by cropland (91±15%), while stream channels (5±2%) 34 and unpaved roads (4±10%) were sources of minor importance. Cropland contribution increased 35 with the drained cropland surface area. The unambiguous dominance of cropland as the main 36 source supplying sediment to the Guaporé River justifies the urgent need to better plan land use 37 and to promote the adoption of appropriate conservation farming practices in similar areas of 38 Southern Brazil. Soil losses in cropland could be reduced by implementing crop rotation, 39 mechanical runoff control strategies, and by avoiding the construction of unpaved roads in 40 thalwegs. 41 42

Negative effects of parasites on their hosts are well documented, but the proximate mechanisms by which parasites reduce their host’s fitness are poorly understood. For example, it has been suggested that parasites might be energetically demanding. However, a recent meta-analysis suggests that they have statistically insignificant effects on host resting metabolic rate (RMR). It is possible, though, that energetic costs associated with parasites are only manifested during and/or following periods of activity. Here, we measured CO2 production (a surrogate for metabolism) in Mediterranean geckos (Hemidactylus turcicus) infected with a lung parasite, the pentastome Raillietiella indica, under two physiological conditions: rested and recently active. In rested geckos, there was a negative, but non-significant association between the number of pentastomes (i.e., infection intensity) and CO2 production. In recently active geckos (chased for 3 minutes), we recorded CO2 production from its maximum value until it declined to a stationary phase. We analyzed this decline as a 3 phase function (initial decline, secondary decline, stationary). Geckos that were recently active showed, in the secondary phase, a significant decrease in CO2 production as pentastome intensity increased. Moreover, duration of the secondary phase showed a significant positive association with the number of pentastomes. These results suggest that the intensity of pentastome load exerts a weak effect on the metabolism of resting geckos, but a strong physiological effect on geckos that have recently been active; we speculate this occurs via mechanical constraints on breathing. Our results provide a potential mechanism by which pentastomes can reduce gecko fitness.