Food Resources

Changes in climate, food abundance and disturbance from humans threaten the ability of species to successfully use stopover sites and migrate between non-breeding and breeding areas. To devise successful conservation strategies for migratory species we need to be able to predict how such changes will affect both individuals and populations. Such predictions should ideally be process-based, focusing on the mechanisms through which changes alter individual physiological state and behavior. In this study we use a process-based model to evaluate how Black Brant (Branta bernicla nigricans) foraging on common eelgrass (Zostera marina) at a stopover site (Humboldt Bay, USA), may be affected by changes in sea level, food abundance and disturbance. The model is individual-based, with empirically based parameters, and incorporates the immigration of birds into the site, tidal changes in availability of eelgrass, seasonal and depth-related changes in eelgrass biomass, foraging behavior and energetics of the birds, and their mass-dependent decisions to emigrate. The model is validated by comparing predictions to observations across a range of system properties including the time birds spent foraging, probability of birds emigrating, mean stopover duration, peak bird numbers, rates of mass gain and distribution of birds within the site: all 11 predictions were within 35% of the observed value, and 8 within 20%. The model predicted that the eelgrass within the site could potentially support up to five times as many birds as currently use the site. Future predictions indicated that the rate of mass gain and mean stopover duration were relatively insensitive to sea level rise over the next 100 years, primarily because eelgrass habitat could redistribute shoreward into intertidal mudflats within the site to compensate for higher sea levels. In contrast, the rate of mass gain and mean stopover duration were sensitive to changes in total eelgrass biomass and the percentage of time for which birds were disturbed. We discuss the consequences of these predictions for Black Brant conservation. A wide range of migratory species responses are expected in response to environmental change. Process-based models are potential tools to predict such responses and understand the mechanisms which underpin them.

Herbivory is a fundamental process that controls primary producer abundance and regulates energy and nutrient flows to higher trophic levels. Despite the recent proliferation of small-scale studies on herbivore effects on aquatic plants, there remains limited understanding of the factors that control consumer regulation of vascular plants in aquatic ecosystems. Our current knowledge of the regulation of primary producers has hindered efforts to understand the structure and functioning of aquatic ecosystems, and to manage such ecosystems effectively. We conducted a global meta-analysis of the outcomes of plant–herbivore interactions using a data set comprised of 326 values from 163 studies, in order to test two mechanistic hypotheses: first, that greater negative changes in plant abundance would be associated with higher herbivore biomass densities; second, that the magnitude of changes in plant abundance would vary with herbivore taxonomic identity. We found evidence that plant abundance declined with increased herbivore density, with plants eliminated at high densities. Significant between-taxa differences in impact were detected, with insects associated with smaller reductions in plant abundance than all other taxa. Similarly, birds caused smaller reductions in plant abundance than echinoderms, fish, or molluscs. Furthermore, larger reductions in plant abundance were detected for fish relative to crustaceans. We found a positive relationship between herbivore species richness and change in plant abundance, with the strongest reductions in plant abundance reported for low herbivore species richness, suggesting that greater herbivore diversity may protect against large reductions in plant abundance. Finally, we found that herbivore–plant nativeness was a key factor affecting the magnitude of herbivore impacts on plant abundance across a wide range of species assemblages. Assemblages comprised of invasive herbivores and native plant assemblages were associated with greater reductions in plant abundance compared with invasive herbivores and invasive plants, native herbivores and invasive plants, native herbivores and mixed-nativeness plants, and native herbivores and native plants. By contrast, assemblages comprised of native herbivores and invasive plants were associated with lower reductions in plant abundance compared with both mixed-nativeness herbivores and native plants, and native herbivores and native plants. However, the effects of herbivore–plant nativeness on changes in plant abundance were reduced at high herbivore densities. Our mean reductions in aquatic plant abundance are greater than those reported in the literature for terrestrial plants, but lower than aquatic algae. Our findings highlight the need for a substantial shift in how biologists incorporate plant–herbivore interactions into theories of aquatic ecosystem structure and functioning. Currently, the failure to incorporate top-down effects continues to hinder our capacity to understand and manage the ecological dynamics of habitats that contain aquatic plants.

There is an urgent need for sustainable animal production systems. A system or procedure is sustainable if it is acceptable now and if its expected future effects are acceptable, in particular in relation to resource availability, consequences of functioning and morality of action. What might make any animal usage system unsustainable? The system might involve depletion of resources such that a resource becomes unavailable, or a product of the system might accumulate to a degree that prevents the functioning of the system. However, any effect which the general public find unacceptable makes a system unsustainable. A production system might be unsustainable because of: inefficient usage of world food resources; adverse effects on human health; poor welfare of animals; harmful environmental effects such as low biodiversity or insufficient conservation; unacceptable genetic modification; not being “fair trade” in that producers in poor countries are not properly rewarded; or damage to rural communities. Consumers might judge, because of any of these inadequacies, that the quality of the product is poor. Animal welfare is a component of sustainability and good quality of product. Three-level plant production, including pasture, shrubs with edible leaves and trees that may also have edible leaves are an example of a silvopastoral system. The production of leaves and other material that can be eaten by the animals is much greater than can be achieved by pasture-only systems.  Results presented from tropical and sub-tropical studies show that production of cattle and other animals can be better, biodiversity much increased, animal disease reduced, and animal welfare improved in three-level silvopastoral systems.
Rev. Bras. Zootec., 46, 683-688. doi.org/10.1590/S1806-92902017000800009

Food resources of the straw-colored fruit bats Eidolon helvum (Kerr, 1792), a near-threaned species in Abidjan-Plateau were studied from August 2007 to July 2008. Faeces collection under sleeping trees and direct observations were made in order to access qualitative composition and temporal distribution of food resources of Eidolon helvum. Results show that 16 species of plants grouped into eight families and classified in three categories of plant organs were exploited by these bats. Among them, three species of plants appeared for the first time in the diet of the frugivorous bats in Côte d'Ivoire. Fruit food resources were most abundant (83%) and fruits of Ficus genus were dominant (45%). The distribution of food resources varied with the season.

The fauna inhabiting a small area (ca. 5 cm x 5 cm) were investigated in a Scots pine stand. After microstratification of the litter layers in the field and fixation in 95% ethyl alcohol, invertebrates, mainly mesofauna, were sorted under a dissecting microscope and mounted or dissected in order to study their intestinal guts. Faeces were mounted or sectioned to obtain information about the activity of other invertebrate groups not represented in the sample and to follow the fate of plant and microbial material after defaecation occurred. Plant material, mainly from moss, bracken, pine needles and bark, was extensively consumed by enchytraeid and lumbricid worms, sciarid larvae and phthiracarid mites. Fungal material was ingested by all groups, either in combination with plant material or alone (camisiid and oppiid mites, some species of Collembola, sciarid and chironomid larvae). Isotomid springtails and chironomid larvae appeared to consume faecal material. The choice and the degree of comminution and digestion of the material differed greatly from one group to another, but without any indication of resource sharing.

Litter and soil communities of Collembola (Insecta, Apterygota) in a mixed deciduous forest in France were studied for four years after experimental litter removal and doubling. Total abundance was unaffected by these two treatments but substantial changes in species composition occurred at the soil surface. Epigeic groups (Entomobryoidea, Symphypleona) almost disappeared in the no-litter treatment, except for the genus Sminthurides whose abundance increased after litter disappearance. Doubling of litter had no significant effect on the Collembola abundance. Relative influences of shifts in habitat structure and food resources are discussed, together with a comparison between macrofaunal and mesofaunal responses to litter manipulations.