Foraging in space and time structure an African small mammal community

We used live-trapping and foraging to test for the effect of habitat selection and diet on structuring a community of six small mammals and one bird within the Soutpansberg, South Africa. We established grids that straddled adjacent habitats: woodland, rocky hillside, and grassland. Trapping and foraging were used to estimate abundance, habitat use, and species-specific foraging costs. The species with the highest abundance and foraging activity in a habitat, activity time, or food was considered the most efficient and presumed to have a competitive advantage. All species exhibited distinct patterns of spatial and temporal habitat preference which provided the main mechanism of coexistence, followed by diet selection. The study species were organized into three assemblages (α diversity): grassland, Rhabdomys pumilio, Dendromus melanotis, and Mus minutoides.; woodland, Aethomys ineptus and Micaelamys namaquensis; and rock-dwelling, M. namaquensis and Elephantulus myurus. Francolinus natalensis foraged in open rocky areas and under wooded islands within the grassland. Species organization across the habitats suggested that feeding opportunities are available within all habitats; however, distinct habitat preferences resulted from differing foraging aptitudes and efficiencies of the competing species. At Lajuma, species distribution and coexistence are promoted through distinct habitat preferences that were shaped by competition and species-specific foraging costs. The combination of trapping and foraging provided a mechanistic approach that integrates behavior into community ecology by ‘asking’ the animal to reveal its perspective of the environment. Using spatial and temporal foraging decisions—as behavioral indicators—enables us to guide our understanding for across-taxa species coexistence.     

Daily torpor in elephant shrews (Macroscelidea: Elephantulus spp.) in response to food deprivation

Patterns of daily torpor were measured in response to photoperiod and food restriction at a constant temperature (18 °C) in two species of elephant shrew (Macroscelidea), Elephantulus rozeti (from Morocco) and Elephantulus myurus (from southern Africa). Body temperature was monitored continuously for ca. 3 months using temperature-sensitive telemeters. Under short photoperiods (8:16 L:D), both species entered spontaneous torpor on an ad libitum diet, but showed a higher frequency of induced torpor when food was restricted. Under long photoperiods (16:8 L:D), E. myurus could be induced to enter daily `summer' torpor. A total of 378 torpor bouts were measured, none of which were longer in duration than 18 h. Under short photoperiods, arousal from torpor was associated with the onset of the photoperiod, whereas the time of entry was variable throughout the scotophase. However, E. myurus tended to phase shift torpor from the photophase to the scotophase under long photoperiods, despite displaying weak circadian amplitudes of body temperature indicative of a photophase rest phase. Both species lacked well-defined circadian amplitudes of body temperature, a pattern thought to be associated with polyphasic activity cycles characteristic of several Elephantulus species. It was concluded that these and other patterns of torpor shown by Elephantulus show similarities with other small Afrotropical insectivores inhabiting semi-arid habitats or unpredictable environments. Accepted: 26 July 2000     

Noradrenalin induces thermogenesis in a phylogenetically ancient eutherian mammal, the rock elephant shrew, Elephantulus myurus

The evolution of endothermy is thought to have been facilitated by the advent of endothermic energy sources such as brown adipose tissue (BAT), the principal site of non-shivering thermogenesis (NST). In marsupials, heat is primarily produced through shivering and NST in skeletal muscle because BAT is either absent or appears to be non-functional. The most basal group of the eutherian lineage are the Afrotheria. Rock elephant shrews, Elephantulus myurus are amongst the smallest members of the Afrotheria and are also known to use exogenous passive heating. The aim of this study was to determine whether the reliance on passive heating compromised the capacity for thermogenesis in E. myurus. We measured the thermogenic response to noradrenalin (NA) injection in E. myurus acclimated to short photoperiod. The thermogenic response at 25°C was 1.58 ml O₂ g⁻¹ h⁻¹. We used phylogenetically independent analyses to establish how this thermogenic response compared to other eutherians that display classical NST. The thermogenic response of E. myurus was not significantly different from phylogenetically independent allometric predictions. However, it is unclear whether this thermogenic response is indicative of classical NST and molecular data are required to verify the presence of BAT and UCPs in elephant shrews.     

Ecophysiological responses to different forest patch type of two codominant tree seedlings

According to gap‐phase dynamics theory, forests can be divided into four distinct patch types: gap patch (G), building patch (B), mature patch (M), and degeneration patch (D). Varying light conditions across patch types are one of the most important factors affecting the coexistence of vegetation. Mechanisms of coexistence can be understood through detailed knowledge of ecophysiological responses of codominant tree seedlings to patch types. The following study was conducted to determine ecophysiological responses of Cyclobalanopsis glauca (an evergreen broad‐leaved species) and Bothrocaryum controversum (a deciduous broad‐leaved species) to four different patch types. During the gap‐phase dynamics, light intensity and the magnitude of change in the four different patches followed the order of: G > B > D > M. Both species had the greatest photosynthetic capacity in the G patch. Dry leaf mass per area (LMA), Chlorophyll a + b concentration (Chl), carotenoids (Car), and nitrogen content per area (N_a) all responded to changes in light across patch type, but B. controversum showed greater sensitivity and changes than C. glauca. From G to M patch, the maximal quantum efficiency of PSII (F_v/F_m) had a larger variation magnitude for B. controversum than for C. glauca. From G to M patch, B. controversum showed significant changes in gas exchange, while C. glauca showed only small changes. Ecophysiological trait partitioning of response to light in different patches provides a possible explanation of a coexistence mechanism.     

Patch area, substrate depth, and richness affect giving-up densities: a test with mourning doves and cottontail rabbits

We compared the foraging behavior of mourning doves Zenaida macroura and cottontail rabbits Sylvilagus floridanus in patches that varied in initial food abundance, surface area and substrate depth. We measured giving‐up densities (GUD), food harvest and proportion of food harvested to investigate their ability to respond to characteristics of resource patches. GUDs have been analyzed in three ways: grams of per patch, grams per unit surface area (GUD_AREA), and grams per unit volume of sand (GUD_VOL). Mourning doves and cottontails exhibited similar responses to resource density and sand depth. Both foragers detected and responded to variation in initial food abundance. The proportion of food harvested from a patch increased from 40.7, 43.8 to 48.3% (for the doves) and 34.9, 35.8 to 38.4% (for the rabbits) in patches of low, medium and high initial food abundance, respectively. Deeper substrates reduced the foragers’ encounter probability with food, decreased patch quality and resulted in higher GUDs (60% higher in the deepest relative to shallowest substrate) and lower harvests. A significant interaction between initial food abundance and substrate depth showed that both species were willing to dig deeper in patches with higher resource density. Patch size (surface area) had no effect on food harvest or the proportion of food harvested. Consequently, GUD_AREA and GUD_VOL increased in patches with a smaller surface area. Smaller patches appeared to hamper the dove's and cottontail's movement across the surface. Our results revealed that mourning doves and cottontails forage under imperfect information. Both species were able to respond to patch properties by biasing their feeding efforts toward rich and easy opportunities, however, mourning doves were more efficient at food harvesting. The interaction of patch area, volume and food abundance directly influenced food harvest. Such resource characters occur under natural situations where food varies in abundance, area of distribution, and accessibility.     

Heterothermy in elephant shrews, Elephantulus spp. (Macroscelidea): daily torpor or hibernation?

The physiological parameters of heterothermy (e.g. minimum body temperature and oxygen consumption, percentage metabolic reduction, and bout length) were measured in two species of Elephantulus elephant shrews (Elephantulus myurus and Elephantulus rozeti; Macroscelidea) as a function of ambient temperature. Both species displayed deep torpor whereby the body temperatures of ca. 5 °C and oxygen consumption as low as 2% of basal metabolic rate were attained. Torpor bout length (n=57 bouts) never exceeded 24 h. These data are characteristic of both hibernation (minimum body temperature and metabolism) and daily torpor (bout length), and argue that these two physiological responses may not necessarily have separate evolutionary origins. Accepted: 26 July 2000     

Colony foraging allocation is finely tuned to food distance and sweetness even close to a bee colony

Social bee colonies can allocate their foraging resources over a large spatial scale, but how they allocate foraging on a small scale near the colony is unclear and can have implications for understanding colony decision‐making and the pollination services provided. Using a mass‐foraging stingless bee, Scaptotrigona pectoralis (Dalla Torre) (Hymenoptera: Apidae: Meliponini), we show that colonies will forage near their nests and allocate their foraging labor on a very fine spatial scale at an array of food sources placed close to the colony. We counted the foragers that a colony allocated to each of nine feeders containing 1.0, 1.5, or 2.0 M sucrose solution [31, 43, and 55% sucrose (wt/wt), respectively] at distances of 10, 15, and 20 m from the nest. A significantly greater number of foragers (2.6–5.3 fold greater) visited feeders placed 10 vs. 20 m away from the colony. Foraging allocation also corresponded to food quality. At the 10‐m feeders, 4.9‐fold more foragers visited 2.0 M as compared to 1.0 M sucrose feeders. Colony forager allocation thus responded to both differences in food distance and quality even when the travel cost was negligible compared to normal colony foraging distances (10 m vs. an estimated 800–1 710 m). For a nearby floral patch, this could result in unequal floral visitation and pollination.     

Bridge under troubled water: Turbulence and niche partitioning in fish foraging

The coexistence of competing species relies on niche partitioning. Competitive exclusion is likely inevitable at high niche overlap, but such divide between competitors may be bridged if environmental circumstances displace competitor niches to enhance partitioning. Foraging‐niche dimension can be influenced by environmental characteristics, and if competitors react differently to such conditions, coexistence can be facilitated. We here experimentally approach the partitioning effects of environmental conditions by evaluating the influence of water turbulence on foraging‐niche responses in two competing fish species, Eurasian perch Perca fluviatilis and roach Rutilus rutilus, selecting from planktonic and benthic prey. In the absence of turbulence, both fish species showed high selectivity for benthic chironomid larvae. R. rutilus fed almost exclusively on zoobenthos, whereas P. fluviatilis complemented the benthic diet with zooplankton (mainly copepods). In turbulent water, on the other hand, the foraging‐niche widths of both R. rutilus and P. fluviatilis increased, while their diet overlap simultaneously decreased, caused by 20% of the R. rutilus individuals turning to planktonic (mainly bosminids) prey, and by P. fluviatilis increasing foraging on littoral/benthic food sources. We show that moderate physical disturbance of environments, such as turbulence, can enhance niche partitioning and thereby coexistence of competing foragers. Turbulence affects prey but not fish swimming capacities, with consequences for prey‐specific distributions and encounter rates with fish of different foraging strategies (pause‐travel P. fluviatilis and cruise R. rutilus). Water turbulence and prey community structure should hereby affect competitive interaction strengths among fish species, with consequences for coexistence probability as well as community and system compositions.     

Test of Competitive Interactions for Space Between Two Benthic Fish Species, Burbot Lota lota, and Stone Loach Barbatula barbatula

The substrate preferences, growth rates and foraging efficiency of two small benthic fish species, juvenile burbot, Lota lota, and stone loach, Barbatula barbatula, were compared in combined outdoor mesocosm and indoor laboratory experiments. Both species preferred the same stony substrate when alone, but significant differences in habitat selection were found between the two species under food deprivation and competition conditions. In burbot, preference for the stony habitat was reinforced under food-deprivation conditions and became even stronger when a potential competitor, the stone loach, was present. In contrast, stone loach switched to the gravel substrate when either starving or in the presence of a heterospecific competitor. Growth rates and foraging efficiency of burbot were significantly highest in the stony substrate and decreased with finer substrates. In stone loach, neither growth rates nor foraging efficiency were significantly different among the different substrates. The results provide an example of habitat partitioning by means of different competition styles, with a stenoecious, dominant style of the burbot and an euryoecious, evasive style of stone loach allowing coexistence of two sympatric fish species by graded interactions at an individual level in the littoral zone of a large lake.     

Foraging and habitat use of common duikers,Sylvicapra grimmia,in a heterogeneous environment within the Soutpansberg,South Africa

We investigated aspects of the foraging behaviour and activity patterns of free‐ranging common duikers (Sylvicapra grimmia) within the Soutpansberg, South Africa. We used giving‐up densities (GUD) and camera traps to test for habitat selection and patch‐use behaviour by common duikers inhabiting a grassland containing distinct ‘islands' of woody vegetation. Foraging in or around a wooded island was affected by its surrounding vegetation. GUDs were significantly lower in portions dominated by tall grass and scattered ferns and highest in areas with open short grass and thick fern. Using grids of 5 × 5 stations, we mapped the duikers' foraging on a larger scale that incorporated neighbouring rocky hillsides. The duikers preferred feeding in areas with tall grass and scattered fern (sufficient cover and escape routes), followed by the wooded islands and thick fern (lack of sightlines/escape routes and presence of predator‐ambush sites), whereas little foraging occurred at the edges and rocky areas (hard substrate that impede escape potential). Photos (total 873) revealed solitary activity, highest in the late afternoon. Photos of vigilant individuals were mostly from rocky and fern habitats. Our results suggest that the duikers allocated their feeding efforts, activity and vigilance patterns to attune to their perceived risk of predation within their heterogeneous environment.     

Reciprocal intraguild predation and predator coexistence

Intraguild predation is a mix of competition and predation and occurs when one species feeds on another species that uses similar resources. Theory predicts that intraguild predation hampers coexistence of species involved, but it is common in nature. It has been suggested that increasing habitat complexity and the presence of alternative food may promote coexistence. Reciprocal intraguild predation limits possibilities for coexistence even further. Habitat complexity and the presence of alternative food are believed to promote coexistence. We investigated this using two species of predatory mites, Iphiseiodes zuluagai and Euseius concordis, by assessing co‐occurrence in the field and on arenas differing in spatial structure in the laboratory. The predators co‐occured on the same plants in the field. In the laboratory, adults of the two mites fed on juveniles of the other species, both in the presence and the absence of a shared food source, showing that the two species are involved in reciprocal intraguild predation. Adults of I. zuluagai also attacked adults of E. concordis. This suggests limited possibilities for coexistence of the two species. Indeed, E. concordis invariably went extinct extremely rapidly on arenas without spatial structure with populations consisting of all stages of the two predators and with a shared resource. Coexistence was prolonged on host plant leaves with extra food sources, but E. concordis still went extinct. On small, intact plants, coexistence of the two species was much longer, and ended with the other species, I. zuluagai, often going extinct. These results suggest that spatial structure and the presence of alternative food increase the coexistence period of intraguild predators.     

Influence of prey encounter and prey identity on area-restricted searching in the lizard Pedioplanis namaquensis

We experimentally determined that the lizard Pedioplanis namaquensis engages in area-restricted searching (=ARS, localized searching after encounters with food) while foraging and that prey characteristics influence ARS. Single prey items were introduced to free-ranging lizards, and their subsequent search effort was characterized using first passage times (=FPT, time required for an animal to cross a circle of a given radius). Three prey types were used: termites, flies, and rice (control). FPTs were longer following termite encounters than following fly or control encounters. Control treatments produced no change in FPT, while lizards searching for termites showed the greatest change. The use by Pedioplanis namaquensis of ARS was most pronounced for the typically aggregated prey type.     

Colony and Individual Forager Responses to Food Quality in the New World Bumble Bee, Bombus occidentalis

The ability of a successful forager to activate colony foraging allows colonies to rapidly exploit ephemeral resources and is an important innovation in the evolution of sociality. We tested the ability of the species, Bombus occidentalis, to stimulate colony foraging for food varying in quality. We then analyzed the behavior of successful foragers inside the nest to learn more about potential foraging activation movements. The number of bees entering a foraging arena was positively correlated with food sucrose concentration (0.5, 1.0, and 2.5 M sucrose, equal to 16–65% w/w). Foragers spent significantly more time imbibing higher concentration solutions. Foragers then returned to the nest where they moved in elaborate paths at variable speeds. There was no significant effect of sucrose concentration on average forager velocity or time spent inside the nest. However, the length of a forager’s path inside the nest (total of all distances moved each 0.1 s) significantly increased with sucrose concentration. On average, individuals foraging on 2.5 M and 1.0 M solution walked paths respectively 1.6 fold and 1.4 longer than the paths of individuals foraging on 0.5 M solution. These longer paths could result in a greater number of nestmate contacts, a factor shown to be important in the activation of B. impatiens foragers and also reported in B. terrestris foragers.     

Reduction of predation risk under the cover of darkness: Avoidance responses of mayfly larvae to a benthic fish

Summary Mayfly larvae of Paraleptophlebia heteronea (McDunnough) had two antipredator responses to a nocturnal fish predator (Rhinichthys cataractae (Valenciennes)): flight into the drift and retreat into interstitial crevices. Drift rates of Paraleptophlebia abruptly increased by 30 fold when fish were actively foraging in the laboratory streams but, even before fish were removed, drift began returning to control levels because larvae settled to the substrate and moved to areas of low risk beneath stones. This drifting response was used as an immediate escape behavior which likely decreases risk of capture from predators which forage actively at night. Surprisingly, drift most often occurred before contact between predator and prey, and we suggest that in darkness this mayfly may use hydrodynamic pressure waves for predator detection, rather than chemical cues, since fish forage in an upstream direction. Although drifting may represent a cost to mayfly larvae in terms of relocation to a new foraging area with unknown food resources, the immediate mortality risk probably out-weighs the importance of staying within a profitable food patch because larvae can survive starvation for at least 2 d. In addition to drifting, mayflies retreated from upper, exposed substrate surfaces to concealed interstitial crevices immediately after a predator encounter, or subsequent to resettlement on the substrate after predator-induced drift. A latency period was associated with this response and mayflies remained in these concealed locations for at least 3 h after dace foraging ceased. Because this mayfly feeds at night and food levels are significantly lower in field refugia under stones, relative to exposed stone surfaces, predator avoidance activity may limit foraging time and, ultimately, reduce the food intake of this stream mayfly.     

Demography of Euterpe precatoria and Mauritia flexuosa in the Amazon: application of integral projection models for their harvest

Non‐Timber Forest Products like palm fruits are fundamental in the livelihood of Amerindian groups. For the last 10 years the fruits of wild palm species, like Euterpe precatoria and Mauritia flexuosa, have been entering into global markets. These species are mostly harvested felling the adults, a practice that may have a disproportionate impact in the conservation of the populations. We studied the demography of E. precatoria and M. flexuosa, two important palms of the Amazon, using integral projection models, to characterize the population dynamics and project impact of different fruit harvest methods: adult felling and direct fruit harvest. We followed over 1400 individuals from populations with low harvest intensities in the Tikuna community of Amacayacu, Amazonas, Colombia from 2011 to 2013, establishing four plots for E. precatoria in seasonally inundated forests and two for M. flexuosa in swamps. The population growth in E. precatoria was slightly declining, whereas M. flexuosa was stable. As expected, the simulations of adult felling diminished λ and the number of available adults under any scenario for either species. On the contrary, the simulations support existing information that climbing and other non‐destructive harvest methods would probably allow a sustainable management, satisfying the demand and preserving wild populations.     

Foraging costs and accessibility as determinants of giving-up densities in a swan-pondweed system

We measured the patch use behaviour of Bewick's swans (Cygnus columbianus bewickii) feeding on below ground tubers of fennel pondweed (Potamogeton pectinatus). We compared the swans’ attack rates, foraging costs and giving‐up densities (GUDs) in natural and experimental food patches that differed in water depth. Unlike most studies that attribute habitat‐specific differences in GUDs to predation risk, food quality or foraging substrate, we quantified the relative importance of energetic costs and accessibility. Accessibility is defined as the extent to which the animal's morphology restricts its harvest of all food items within a food patch. Patch use behaviours were measured at shallow (ca 0.4 m) and deep (ca 0.6 m) water depths on sandy sediments. In a laboratory foraging experiment, when harvesting food patches, the swan's attack rate (m³ s^?1) did not differ between depths. In deep water the energetic costs of surfacing, feeding and trampling were 1.13 to 1.21 times higher than in shallow water with a tendency to spend relatively more time trampling, the most expensive activity. Taking time allocation as measured in the field into account, foraging in deep water was 1.26 times as expensive as in shallow water. In the lake the GUD in shallow water was on average 12.9 g m^?2. If differences in energetic costs were the only factor determining differences in GUDs, then the deep water GUD should be 14.2 g m^?2. Instead, the mean GUD in deep water was 20.2 g m^?2, and therefore energetic costs explain just 18% of the difference in GUDs. At deep sites, 24% of tuber biomass was estimated to be out of reach, and we calculated a maximum accessible foraging depth of 0.86 m. This is close to the published 0.84 m based on body measurements. A laboratory experiment with food offered at a depth of 0.89 m confirmed that it was just out of reach. The agreement between calculated and observed maximum accessible foraging depths suggests that accessibility largely explains the remaining difference in GUDs with depth, and it confirms the existence of partial prey refuges in this system.     

Taxonomic status of the Forest Buzzard Buteo oreophilus trizonatus

The foraging efficiencies of four sympatric southern African seed-eating birds, namely Bronze Mannikin Spermestes cucullatus, Cape Sparrow Passer melanurus, Southern Red Bishop Euplectes orix and Thick-billed Weaver Amblyospiza albifrons, and a domesticated species, the Bengalese Finch Lonchura domestica, were measured and compared using giving-up densities (the amount of food remaining following patch exploitation) in experimental food patches. Foraging efficiency was quantified using giving-up densities by offering individual birds equal foraging opportunities. A low giving-up density displays the ability of a forager to profitably harvest food at low resource densities and to gainfully exploit the foraging opportunities overlooked by a less efficient forager. Ten individuals of each of the five species were allowed to forage on six different seed types. Thick-billed Weavers had significantly lower giving-up densities for all seed types except the smallest, namely red manna. Bronze Mannikins showed the converse trend, foraging most efficiently on the smallest seeds. The results of the present study revealed that Thick-billed Weavers were the most efficient foragers (i.e. had the lowest giving-up densities on seeds in feeding trays).     

Influence of sedimentation in the absence of macrograzers on recruitment of an annual population of Macrocystis pyrifera in Metri Bay,Chile

The effects of sedimentation and substrate orientation on algal and sessile invertebrate assemblages were tested on an annual population of Macrocystis pyrifera in Metri Bay, southern Chile. In the laboratory, M. pyrifera zoospores were seeded on Crepipatella fecunda shells, the primary substrate for M. pyrifera in this system. The seeded shells were deployed at Metri Bay inside cages and were orientated vertically and horizontally under two sedimentation regimes (bottom and suspended). Due to differences in grazer accessibility and the species present between the sedimentation treatments, grazers (>1 cm) were excluded. We followed sporophyte development of M. pyrifera and the natural recruitment of other algal and invertebrate species. Sedimentation rates were significantly higher in the cages attached to the bottom compared to suspended cages (P < 0.001). In total M. pyrifera and three additional algal genera were detected and all algal recruits showed significantly greater recruitment on the horizontally orientated substrate compared to the vertical substrate. Macrocystis pyrifera sporophytes were present only on the horizontal, suspended (less sedimentation) treatment. In contrast, Ulva and Ectocarpus spp. also occurred in the horizontal, high sediment treatment. Invertebrate recruitment (amphipods, barnacles and spirorbids) dominated the vertically oriented shells regardless of sedimentation. Results indicate that high sedimentation negatively affected the development of M. pyrifera sporophytes while other opportunistic species were able to recruit under these conditions.     

Independent trophic behavior and breeding success of a resident flycatcher and a coexisting migratory congener

Historical biases towards the study of Palearctic and Nearctic bird migration systems has resulted in a dearth of information on the ecology of intratropical migrants, which likely also play important ecological roles within their communities. For instance, there is little information on the foraging ecology and breeding biology of co‐occurring migrants and residents within the intratropical migratory system. Thus, we used two congeneric flycatchers – the resident Plain‐crested Elaenia Elaenia cristata (Aves: Tyrannidae), and the migrant Lesser Elaenia E. chiriquensis (Tyrannidae) – to check whether either of them showed foraging niche plasticity mediating their coexistence and the effects of such syntopy on their breeding behavior and fitness. To do so, we used an ensemble of methods that included the evaluation of food resource phenology, foraging behavior observations, stable isotope ratio analysis in birds’ tissues, and nest monitoring. Our results confirmed that residents have foraging behavior plasticity but reveals its trophic behavior and breeding success is independent of the coexistence with migrants. Since such results depart from the predictions based on the current (and often Northern‐biased) theories of bird migration, we discuss alternative hypotheses explaining our findings, including the influence of physiology on diet and the behavioral responses of nest predators. Once there is a clear knowledge gap about the interspecific interactions between residents and intratropical migrants, our study represents a simple, yet important, step towards understanding the mechanisms underlying this system.