Function Of Resource Availability Research Articles

Local Agricultural Management Filters Morphological Traits of the South American Palm Weevil (Rhynchophorus palmarum L.; Coleoptera: Curculionidae) in Ornamental Palm Plantations

Insect pests show phenotypic plasticity as a function of resource availability and limiting conditions. Although Rhynchophorus palmarum displays high variation in certain morphological traits, it is still not clear how and which of these are being filtered along agricultural management gradients in palm plantations. This study assesses the influence of biophysical structure of ornamental palm plantations and agrochemical use on morphological traits of adults in 15 permanent plots of ornamental palm plantations in Veracruz, Mexico. A total of 4972 adults were and their body length, pronotum width, rostrum length, and mesothorax depth were measured. Body length and mesothorax depth of adults of both sexes were greater in plantations with a high diversity of palm species and frequency of fertilizer use. Rostrum length of females increased as a function of palm density, and pronotum width of both sexes was positively related with the use of insecticides. Local characteristics of agricultural management of palm plantations might filter integrated, adaptative, and environment-specific phenotypes. This is the first ecological study of the south American palm weevil that provides new insights on the current intensive management of ornamental palm plantations that far from controlling, benefits current geographic expansion, demographic outbreak, and economic impact of this pest.

Trophic plasticity in the sea urchin Paracentrotus lividus, as a function of resource availability and habitat features

Factors controlling herbivory pressure are of central importance in shaping the seascape. In the Mediterranean, the sea urchin Paracentrotus lividus is considered as a keystone herbivore in seagrass meadows and macroalgal communities. Here we explored the trophic behavior of this sea urchin in a shallow seagrass habitat of Cymodocea nodosa mixed with Caulerpa prolifera and interspersed with sandy areas in Alfacs Bay, Ebro Delta (NW Mediterranean). The seasonal pseudo-indigenous bryozoan Amathia verticillata is locally very abundant, and there is also an important population of pen shells Pinna nobilis, providing hard substrate and cover, thus being a unique environment for assessing sea urchin trophic behavior. To this end, we conducted an ensemble of food preference and foraging experiments and stomach content and stable isotope analyses. Our results showed that sea urchins strongly prefer A. verticillata over other local resources, and there was also an important presence of the bryozoan in stomach contents (ca. 44%), coupled with green and decayed seagrass leaves. Stable isotope analyses revealed that over the long term, ca. 65% of the diet of P. lividus was based on decayed seagrass leaves, followed by the bryozoan and green seagrass leaves (21.7 and 13.3%, respectively). The local availability of P. nobilis provides a preferred substrate for sea urchins, which showed limited foraging movements into the surrounding seagrass beds, particularly when A. verticillata was attached to the pen shells. The apparently high contribution of animal and detrital food to P. lividus diet is unprecedented, and suggests an opportunistic feeding behavior in sea urchins in those habitats.

The habitat functional response links seasonal third-order selection to second-order landscape characteristics.

Determining how animals respond to differences in resource availabilities across spatiotemporal extents is critical to our understanding of organism distributions. Variations in resource distribution leading to changes in spatial arrangements across landscapes are indicative of a habitat functional response. Our goal was to assess how resource availabilities influenced both second‐order (i.e., home ranging behavior) and third‐order (i.e., habitat or resource selection) selection by feral pigs (Sus scrofa) in an agricultural landscape. We defined agriculturally based seasons to estimate home range characteristics using autocorrelated kernel density estimation within each season. We then modeled home range size as a function of resource availability (i.e., resource selection analyses) to determine whether individual behaviors were predicted by shifts in home ranging behavior. Both home range analyses and resource selection analyses indicated seasonal differences in selection for agricultural resources as availabilities changed, suggesting second‐ and third‐order selection is mechanistically linked through a habitat functional response.

Profit stability of mixed dairy and beef production systems of the mountain area of southern Auvergne (France) in the face of price variations: Bioeconomic simulation

Mountain farmers face additional structural constraints (e.g., steep slopes, high elevations, fragmented fields) along with the regular risks inherent to agriculture, such as economic fluctuations. We thus hypothesized that simultaneously producing dairy and beef herds (i.e., “mixed cattle systems”) on mountain farms is a good compromise between a farm's expected profits and the variation in these profits. To explore the profit stability of mixed cattle systems in the face of price variations, we used the bioeconomic optimization model Orfee to simulate one farm strategy: adjusting the number of cattle. The model simulated three mixed cattle systems (dairy and beef herds) and two specialized cattle systems (dairy or beef herd) on two farms in southern Auvergne (France) that differed in agronomic potential, field configurations and animal productivity. A local sensitivity analysis of beef, milk and feed price was combined with a global sensitivity analysis based on metamodels. Results indicated that the number of cattle was adjusted as a function of resource availability, farm structure, and product prices on the market. Compared to specialized systems, mixed cattle systems usually seemed an effective strategy to manage economic risk, with good compromise between expected profits and variation in profits.

Trophic plasticity in P. lividus: herbivory, detritivory and omnivory as a function of resource availability

Trophic plasticity in P. lividus: herbivory, detritivory and omnivory as a function of resource availability

Habitat loss and overhunting synergistically drive the extirpation of jaguars from the Gran Chaco

AbstractAimUnderstanding how habitat loss and overhunting impact large carnivores is important for broad‐scale conservation planning. We aimed to assess how these threats interacted to affect jaguar habitat (Panthera onca) between 1985–2013 in the Gran Chaco, a deforestation hotspot.LocationGran Chaco ecoregion in Argentina, Paraguay and Bolivia.MethodsWe modelled jaguar habitat change from 1985–2013 using a time‐calibrated species distribution model that uses all occurrence data available for that period. We modelled habitat as a function of resource availability and hunting threats, which allowed us to separate core (high resource availability and low hunting threat), refuge (low resources but safe), attractive sink (high resources but risky) and sink (low resources and risky) habitat for 1985, 2000 and 2013.ResultsJaguar core areas contracted by 33% (82,400 km2) from 1985–2013, mainly due to an expansion of hunting threats. Sink and attractive sink habitat covered 58% of the jaguar range in 2013 and most confirmed jaguar kill sites occurred in these areas. Furthermore, habitat loss and hunting threats co‐occurred in 29% of jaguars’ range in 2013. Hunting threats also deteriorated core areas within protected areas, but 95% of all core areas loss occurred outside protected lands. About 68% of the remaining core areas in 2013 remained unprotected, mostly close to international borders.Main conclusionsOur study highlights the synergistic effects that habitat loss and hunting threats exert on large carnivores, even inside protected areas, emphasizing the need to consider the geography of threats in conservation planning. Our results also point to the importance of areas along international borders as havens for wildlife and thus the urgent need for cross‐border planning to prevent the imminent extinction of jaguars from the Chaco. Opportunities lie in reducing jaguar mortality over the widespread attractive sinks, particularly in corridors connecting core areas.

Geographical variation in male territory defence strategies in an avian ring species

Interactions between sexual selection and ecology can drive phenotypic divergence between populations. Geographical variation in female preferences has been linked to ecology in several studies, but much less is known about patterns of geographical variation in male competition. I asked whether male aggressive territorial behaviour varied among three breeding populations of a ring species, the greenish warbler, Phylloscopus trochiloides. I measured aggressive response to playbacks of conspecific song at multiple time points to determine how territorial behaviour varied throughout the breeding season both within and between populations. Differences in the abundance and timing of resources necessary for raising offspring can shape male competitive strategies, and competition may consequently vary as a function of resource availability. I therefore combined assays of temporal variation in aggressive behaviour with season-long measures of food abundance, population density and parental provisioning rates. I found that the populations differed in intensity of aggressive response, the seasonal pattern of territoriality and the traits used in territorial responses. Overall intensity of aggression was lowest but most prolonged in the population with the lowest food abundance and highest population density, and males responded to playback primarily by singing. By contrast, birds in the two populations that experienced high food abundance and low population density exhibited a burst of aggressive display behaviour only when females were fertile. The results suggest that territorial strategies vary geographically and respond to limited resources, switching in function from season-long food defence where food is scarce to mate guarding where mates are scarce. Interactions between sexual selection and ecology across large geographical scales may ultimately lead to population divergence. The geographical variation in territorial behaviour observed in the greenish warbler implies that male competition may be an important diversifying force in this system.

Resource Availability Drives Mating Role Selection in a Simultaneous Hermaphrodite Aplysia californica.

In simultaneous hermaphrodites, a clear conflict exists between sperm donor and sperm recipient roles, and how such conflict is mediated remains up for debate. This study observed and recorded mating role selection as a function of resource availability in the simultaneous hermaphrodite Aplysia californica. When food was plentiful, animals assumed both sperm donor and recipient roles at relatively even frequency. However, when half of the mating pairs were placed on restricted diets, food-limited animals assumed the sperm donor role at significantly (P < 0.05) greater frequency than their ad libitum partners; nevertheless, the frequency of successful mating events remained the same. The mass and frequency of eggs laid were also significantly (P > 0.05) correlated with parental food intake. These results demonstrate how mating strategies can change within a mating season, as a result of shifting environmental conditions, and call for a diverse framework to address these issues in simultaneous hermaphroditic mating systems.

Integrating social network analysis and fine-scale positioning to characterize the associations of a benthic shark

Many shark species form groups; yet the drivers of this behaviour are not well understood. Aggregations have been presumed to be a function of resource availability or phenology. However, recent studies have suggested that some sharks display preferences in their associations with conspecifics and that complex social networks may underpin their movement patterns, demographic distribution and fitness. This study used a network approach to investigate patterns of sociality of a benthic predator, the spotted wobbegong shark, Orectolobus maculatus (Family Orectolobidae), in a small marine reserve. Spatial data obtained from fine-scale passive acoustic telemetry were used to infer association preferences of 15 tagged sharks over a 15-month period. Thirty-five associating dyads emerged, with permutation tests indicating that these were nonrandomly formed. Many dyads were temporally stable, with some persisting even after sharks returned to the reserve from their seasonal migration. A complete but sparse network was observed and although association patterns were evident at the dyadic level, indication of stable communities or network structure was limited. The population was not found to be gregarious and exclusive pairs were not observed, with 14 sharks associating with more than one individual. Assortative mixing (by sex, size and familiarity) was not present and range overlap did not strongly correlate with association indices. This suggests that these relationships are not a random result of nonsocial grouping behaviours but can be explained, at least in part, by genuine social affiliation. As such, anthropogenic influences on the population may have more complex impacts than previously thought.

Influence of Resource Availability on the Foraging Strategies of the Triangle Butterflyfish Chaetodon triangulum in the Maldives.

Obligate coral feeders such as many members of the Chaetodontidae family (also known as butterflyfish) often show strong preferences for particular coral species. This is thought to have evolved through natural selection as an energy-maximising strategy. Although some species remain as highly specialised feeders throughout their lifetime, many corallivores show a degree of dietary versatility when food abundance is limited; a strategy described by the optimal foraging theory. This study aimed to examine if, within-reef differences in the feeding regime and territory size of the Triangle Butterflyfish Chaetodon triangulum occurred, as a function of resource availability. Results showed that the dietary specialisation of C. triangulum was significant in both areas of low and high coral cover (χL22 = 2.52 x 102, P<0.001 and χL22 = 3.78 x 102, P<0.001 respectively). Resource selection functions (RSFs), calculated for the two main sites of contrasting coral assemblage, showed that in the resource-rich environments, only two Genera (Acropora and Pocillopora) were preferentially selected for, with the majority of other corals being actively ‘avoided’. Conversely, in territories of lower coral coverage, C. triangulum was being less selective in its prey choice and consuming corals in a more even distribution with respect to their availability. Interestingly, coral cover appeared to show no significant effect on feeding rate, however it was a primary determinant of territory size. The findings of the study agree with the predictions of the optimal foraging theory, in that where food supply is scarce, dietary specialisation is minimised and territory size increased. This results in maximising energy intake. This study represents the first scientific evidence that C. triangulum is an obligate corallivore and, as with many other butterflyfish, is therefore dependent on healthy scleractinian corals for survival.

Reproductive Dynamics of the Neotropical TreefrogHypsiboas albopunctatus(Anura, Hylidae)

Abstract To understand the seasonal reproductive dynamics of Hypsiboas albopunctatus, a Neotropical treefrog, we studied the following components: 1) the influence of abiotic factors on seasonality, 2) how this seasonality relates to population dynamics, and 3) male breeding recruitment. We conducted fieldwork every month from August 2007 to July 2008 within an ecotone connecting semideciduous Atlantic Forest and Cerrado (Brazilian Savanna) in Sao Paulo State, southeastern Brazil. Over the course of the prolonged breeding season, we recorded the maximum number of calling males and measured their snout–vent lengths; we then compared our data from the beginning and the end of the breeding season. We found that the breeding pattern of H. albopunctatus is correlated with climatic, physical, and biological factors. Male competition and aggression varied according to the population density, most likely as a function of resource availability. There appears to be a social hierarchy among males of H. albopunctatus...

The importance of anthropogenic effects in habitat use and territory size of Northern Anteater-chats Myrmecocichla aethiops near Amurum Forest Reserve, Jos-Plateau, Nigeria

Occurrence of animals in an area and the size of territories they occupy is a function of resource availability and the environmental conditions in that area. Territory location in birds is often determined by availability of nesting habitat and we investigate whether this is the case for the little-studied Northern Anteater-chat Myrmecocichla aethiops. Territory size and location were mapped over two months in 2012 at 25 different sites where the birds occurred in central Nigeria and compared to 25 random sites where they did not, 500 m away. Vegetation variables, invertebrate abundance indicators, anthropogenic variables (availability of nest sites) and bird community components were measured and compared with adjoining areas (500 m away) from which the birds were absent in order to determine important factors determining territory location and size. Territories were 1.23 ha (SE 0.14) in size and were widely separated and so non-contiguous. Increasing numbers of abandoned wells, ant nests and termite mounds increased the probability of territory occupation. Territory size increased with the number of anteater-chats but decreased with increasing number of ant nests and overall bird diversity that were probably proxies for habitat quality. Overall, choice of preferred areas for the Northern Anteater-chat was centred on nesting sites and then habitat quality and group size probably determined territory size.

Floral resource availability and hummingbird territorial behaviour on a Neotropical savanna shrub

The influence of floral resource availability on behaviour and dominance hierarchy of hummingbirds has seldom been investigated in open tropical environments. We evaluated the behavioural changes of hummingbirds associated with Palicourea rigida, a shrub common in the Cerrado, the open savanna areas in Central Brazil. We observed the foraging behaviour as a function of resource availability and experimentally manipulated floral display and nectar in order to define resource thresholds associated with territorial behaviour and territory intruding behaviour. Territorial behaviour was observed only in patches with high floral abundance and was restricted to some hummingbird species. The large Eupetomena macroura seems to be the dominant species in the community, excluding other hummingbirds and holding the richest patches. The experimental reduction in the floral abundance and nectar led to the abandonment of territory by these hummingbirds, which reinforces the idea that a certain threshold is necessary to maintain territorial defence. Higher floral display, on the other hand, seems to lead to higher frequency of intrusions and higher behavioural complexity of territory defenders, possibly meaning greater energy expenditure. The flower number and nectar manipulation affected visitation rates of territorial hummingbirds, but the frequency of intruders was affected only by the former manipulation. This indicates that territorial intruder use visual cues (floral abundance) as indicators of resource availability in order to estimate cost–benefit of territory invasion. Although territorial behaviour could limit pollen flow in patches with larger floral displays, this may be compensated by the territory invaders, which bring pollen from other patches.

Olycella aff. junctolineella (Lepidoptera: Pyralidae) florivory on Opuntia microdasys, a Chihuahuan Desert endemic cactus

The object of this study was to provide the first data on the natural history of the little known plant–florivore interaction between Opuntia microdasys and Olycella aff. junctolineella larvae and to study interindividual variability in the number of reproductive structures attacked as a function of plant resource availability. Field observations of larval activity and a quantification of the damages produced were done at the Southern Chihuahuan Desert, Mexico. To quantify the interindividual variation of florivory damage as a function of resource availability (water and nutrients), a resource addition experiment was carried out. Larvae caused 21% of buds and 7% of flowers to abort. Adding resources (water and nutrients) to plants had no effect on bud production, although more buds developed into flowers and fruits in fertilized plants, suggesting a selective abortion against ill-nourished reproductive structures. The number of buds and flowers attacked by larvae were higher for non-fertilized than for fertilized plants, indicating that reproductive structures of plants under abiotic stress become more suitable as food for florivores. The number of structures attacked was a non-linear function of the number of buds originally produced, suggesting a florivore satiation threshold.

Variation in Prokaryotic Community Composition as a Function of Resource Availability in Tidal Creek Sediments

In anaerobic coastal sediments, hydrolytic and/or fermentative bacteria degrade polymeric material and produce labile intermediates, which are used by terminal metabolizers to complete the conversion of organic material to CO(2). We used molecular approaches to evaluate the response of two bacterial terminal metabolizer groups from a coastal tidal creek sediments, sulfate reducers and methanogens, to controlled changes in carbon resource supply. Tidal creek sediment bioreactors were established in April and August 2004. For each date, intact sediment sections were continuously supplied with flowthrough seawater that was either unamended or amended with the high-molecular-weight polysaccharide dextran. Biogeochemical data indicate that the activity of fermenting bacteria and the terminal metabolizers was limited by organic carbon supply during both experiments, with a significant increase in net volatile fatty acid (VFA) production and rates of sulfate reduction and methanogenesis following dextran addition. Community composition (measured by using terminal restriction fragment length polymorphism analysis, and functional gene [dsrA, mcrA] clone libraries) changed from April to August. However, community composition was not different between amended and unamended cores within each month, despite the change in resource level. Moreover, there was no relationship between community richness and evenness with resource level. This lack of variation in community composition with C addition could be attributed to the dynamic environment these sediment communities experience in situ. Fluctuations in VFA concentrations are most likely very high, so that the dominant bacterial species must be able to outcompete other species at both high and low resource levels.

Allometric analysis reveals relatively little variation in nitrogen versus biomass accrual in four plant species exposed to varying light, nutrients, water and CO2

Nitrogen concentrations in plant tissues can vary as a function of resource availability. Altered rates of plant growth and development under varying resource availabilities were examined to determine their effects on changes in whole-plant N use efficiency (NUE). Three species of old-field annuals were grown at broadly varying light, nutrient and water levels, and four species at varying atmospheric concentrations of CO2. Study results show highly variable N accrual rates when expressed as a function of plant age or size, but similar patterns of whole-plant N versus non-N biomass accrual over a wide range of environmental conditions. However, severely light-limited plants showed increased N versus biomass accrual for two of three species, and severely nutrient-limited plants had decreased N versus biomass accrual for all species. Whole-plant N accrual versus age and N versus biomass accrual increased under saturating water for two of three species. A marginally significant, modest decrease in N versus biomass accrual was found at high CO2 levels for two of four species. Physiological adjustments in NUE, expressed as N versus biomass accrual, were limited to environments with severely limited or overabundant resources.

Renewable energy sources: Their global potential for the first-half of the 21st century at a global level: An integrated approach

The risk of human-induced climate change and the volatility of world oil markets make non-fossil fuel options important. This paper investigates the potential for wind, solar-PV and biomass (WSB) to deliver energy. The focus is on land opportunities and constraints and on production costs as a function of resource availability and depletion and of innovation dynamics. The context is provided by the IPCC SRES scenarios as simulated with the IMAGE 2.2 model. We explicitly consider several sources of uncertainty, aspects of the food vs. energy trade-off and the effects of interaction between the three options through their claims on land. We show that ‘potential production’ concepts are strongly dependent on the chosen land-use scenario—and should therefore be used with an indication of the underlying assumptions. Our results indicate a potential for liquid biofuels in the order of 75–300 EJ year −1 and for electricity from WSB options at production costs below 10 ¢ kWh −1 of 200–300 PWh year −1. Theoretically, future electricity demand can be amply met from WSB sources in most regions by 2050 below 10 ¢ kWh −1, but major uncertainties are the degree to which land is actually available and the rate and extent at which specific investment costs can be reduced. In some regions, competition for land among the three WSB options may significantly reduce the total potential as estimated from simple addition—which is another source of uncertainty.

Production as a function of resource availability: Slopes and efficiencies are different

Abstract. A number of investigators have interpreted the slope of a linear production‐resource relationship as a measure of efficiency of resource utilization. However, this is rarely true and may lead to incorrect conclusions. Here, by means of simple mathematical equations and conceptual definitions, we point out the theoretical differences between slope and efficiency. While a slope represents the change in the dependent variable per unit change in the independent variable, efficiency expresses the amount of output produced by a unit amount of input. Practical implications of using slopes as indicators of resource‐use efficiency are less important as the resource amount increases. Slopes may be used as indicators of the sensitivity of production to changes in input, which is by itself an interesting property of biological systems. Finally, production function intercepts determine whether the efficiency will decrease, increase, or remain constant as resources increase.

Production as a function of resource availability: Slopes and efficiencies are different

A number of investigators have interpreted the slope of a linear production-resource relationship as a measure of efficiency of resource utilization. However, this is rarely true and may lead to incorrect conclusions. Here, by means of simple mathematical equations and conceptual definitions, we point out the theoretical differences between slope and efficiency. While a slope represents the change in the dependent variable per unit change in the independent variable, efficiency expresses the amount of output produced by a unit amount of input. Practical implications of using slopes as indicators of resource-use efficiency are less important as the resource amount increases. Slopes may be used as indicators of the sensitivity of production to changes in input, which is by itself an interesting property of biological systems. Finally, production function intercepts determine whether the efficiency will decrease, increase, or remain constant as resources increase.

Should Plants in Resource-Poor Environments Invest More in Antiherbivore Defence?

The resource availability hypothesis' proposes that low resource availability favours plants with inherently slow growth rates. which in turn favours large investments in antiherbivore defence. Here we present a simple model of evolution of plant defence allocation in a system incorporating plant-resource dynamics. and show that taking into account the feedback of plants on the amount of a limiting resource leads to very different predictions than those from the classical resource availability hypothesis. The latter is based on the assumption that fitness is determined by the potential growth rate, hence, implicitly, on the assumption of unlimited growth in a transient environment where plants do not deplete soil resources. In an environment where plants have accumulated enough biomass to control resource concentration, fitness is determined by the ability to deplete limiting resources if the environment is homogeneous or by other traits correlated with biomass or productivity if the environment is spatially structured. In this case, resource supply and maximum growth rate may either increase, decrease, or in most cases not affect al all, optimal defence investment. Much more detailed data about what determines fitness in climax' environments would be necessary to make even qualitative predictions about the direction of evolution of antiherbivore defence investment as a function of resource availability and maximum growth rate.