Distant Patch Research Articles

Late Holocene tule elk (Cervus canadensis nannodes) resource depression and distant patch use in central California: Faunal and isotopic evidence from King Brown and the Emeryville Shellmound

Previous research has documented declines in the abundance of high-return resources including tule elk (Cervus canadensis nannodes) over the past three millennia in central California, suggesting the occurrence of resource depression. We test the hypothesis that hunting depressed tule elk in this setting by articulating stable isotope analyses from 88 directly dated tule elk specimens with data on the age structure and skeletal part representation from the King Brown and Emeryville Shellmound sites. Late Holocene trends in stable isotopes and modeled climatic variation are inconsistent with climate-based population declines. However, at King Brown, located within the Central Valley and vast tule elk freshwater marsh and grassland habitat, increasing isotopic diversity, a decline in mean age, and increasing abundance of high-utility skeletal elements suggest local depression stimulated the increasing use of distant elk patches. Although faunal trends are consistent with the depression of elk at Emeryville, the site is located on the shore of the San Francisco Bay where limited elk habitat existed, and no evidence of distant elk patch use is indicated. This analysis underscores how human behavioral responses to resource depression can vary in relation to the local ecology as they affect patch use economics for specific prey and demonstrates how such responses can be deciphered through stable isotope and faunal data.

Proton Migration on Top of Charged Membranes.

Proton relay between interfacial water molecules allows rapid two-dimensional diffusion. An energy barrier, ΔGr‡, opposes proton-surface-to-bulk release. The ΔGr‡-regulating mechanism thus far has remained unknown. Here, we explored the effect interfacial charges have on ΔGr‡'s enthalpic and entropic constituents, ΔGH‡ and ΔGS‡, respectively. A light flash illuminating a micrometer-sized membrane patch of a free-standing planar lipid bilayer released protons from an adsorbed hydrophobic caged compound. A lipid-anchored pH-sensitive dye reported protons' arrival at a distant membrane patch. Introducing net-negative charges to the bilayer doubled ΔGH‡, while positive net charges decreased ΔGH‡. The accompanying variations in ΔGS‡ compensated for the ΔGH‡ modifications so that ΔGr‡ was nearly constant. The increase in the entropic component of the barrier is most likely due to the lower number and strength of hydrogen bonds known to be formed by positively charged residues as compared to negatively charged moieties. The resulting high ΔGr‡ ensured interfacial proton diffusion for all measured membranes. The observation indicates that the variation in membrane surface charge alone is a poor regulator of proton traffic along the membrane surface.

Membrane composition may regulate proton wave propagation.

Lateral proton diffusion along membrane surfaces, specifically between a proton source and a sink, is a fundamental process in many biological systems. It may play a significant part in the uptake of cations, sugars, amino acids, and ATP synthesis. Fast interfacial diffusion cannot rely on titratable membrane residues, as a comparison with the relatively slow proton release reaction shows [1]. Yet, an entropy-dominated free energy barrier prevents surface protons from equilibrating with bulk protons [2]. The dependence of barrier height on membrane compositions thus far remained enigmatic. To establish the barrier-modulating role of glycolipids, we released protons to a small spot on the surface of planar lipid bilayers by Ca2+ microinjection. The membranes contained a calcium ionophore (A23187) which facilitated the transmembrane transport of Ca2+ ions in exchange for protons [3]. A lipid-anchored pH-sensor allowed detection of the arrival of the locally triggered proton wave on a distant membrane patch as a change in fluorescence intensity. Our results indicated that interfacial sugar moieties might be potent regulators of proton migration between membrane-embedded proton sources and sinks. This project was supported by the Marie Skłodowska-Curie grant 860592 (Horizon 2020). [1] Springer, et al. Proc. Natl. Acad. Sci. U.S.A, 2011, 108, 14461-14466. [2] Weichselbaum, et al. Scientific Reports, 2017, 7, 4553. [3] Peter Pohl, Yuri N. Antonenko, Lev S. Yaguzhinsky, Biochimica et Biophysica Acta, 1990, 1027, 295-300.

Functional connectivity in ruminants: A generalized state-dependent modelling approach.

Animal behaviour is increasingly seen as an important component in maintaining functional connectivity between patches in fragmented landscapes. However, models that explicitly incorporate behavioural trade-offs are rarely applied to landscape planning problems like connectivity. The aim of this study was to explore how state-dependent behaviour influenced functional connectivity between patches from a theoretical perspective. We investigated how inter-patch distances influenced functional connectivity using a dynamic state variable model framework. The decision making process of an individual ruminant facing fitness trade-offs in staying in its patch of origin or moving to another patch at various distances were explicitly modelled. We incorporated energetic costs and predation costs of feeding, ruminating, and resting while in the patch and for transit between patches based on inter-patch distance. Functional connectivity was maintained with isolated patches when they offered high intake and the inactivity of rumination associated with rapid gut fill resulted in reduced predation risk. Nevertheless, individuals in high energetic state often would forgo moving to another patch, whereas individuals in poor energetic states were forced to accept the cost of movement to best meet their requirements in the distant patch. The inclusion of state-dependent behavioural models provides important insights into functional connectivity in fragmented landscapes and helps integrate animal behaviour into landscape planning. We discuss the consequences of our findings for landscape planning to show how the approach provides a heuristic tool to assess alternative scenarios for restoring landscape functional connectivity.

Origin of proton affinity to membrane/water interfaces

Proton diffusion along biological membranes is vitally important for cellular energetics. Here we extended previous time-resolved fluorescence measurements to study the time and temperature dependence of surface proton transport. We determined the Gibbs activation energy barrier ΔG‡r that opposes proton surface-to-bulk release from Arrhenius plots of (i) protons’ surface diffusion constant and (ii) the rate coefficient for proton surface-to-bulk release. The large size of ΔG‡r disproves that quasi-equilibrium exists in our experiments between protons in the near-membrane layers and in the aqueous bulk. Instead, non-equilibrium kinetics describes the proton travel between the site of its photo-release and its arrival at a distant membrane patch at different temperatures. ΔG‡r contains only a minor enthalpic contribution that roughly corresponds to the breakage of a single hydrogen bond. Thus, our experiments reveal an entropic trap that ensures channeling of highly mobile protons along the membrane interface in the absence of potent acceptors.

Regulation of Proton Migration along the Membrane Surface

Proton diffusion along biological membranes is vitally important for cellular energetics. Both migration speed and span weakly depend on the presence of titratable residues, suggesting that interfacial water molecules serve as proton railways (1). This hypothesis is supported by (i) the observation of proton migration along the water-decane interface and (ii) ab initio simulations that demonstrate proton travel along structured water molecules in the second hydration shell of this interface (2). To test the importance of interfacial water structure, we have now monitored proton migration along the membrane surface in the presence of DMSO. Therefore, we photoreleased protons from a membrane-adsorbed caged compound by illuminating a small patch of a planar lipid bilayer, and we monitored their arrival at a distant membrane patch by measuring the fluorescence of the membrane-anchored pH dye. The synthesis of these caged protons is outlined on the poster of Österbauer et al. DMSO facilitated proton surface-to-bulk release and decreased the surface proton diffusion constant as has been anticipated from its disturbing effect on the hydration layer of membranes. We conducted similar experiments with osmolytes, which likewise affect membrane hydration. Finally we tested the effect electrostatic attraction of protons may have on their surface migration. The presence of negatively charged lipids decreased both the rate of proton surface-to-bulk release and the surface diffusion constant. We conclude that proton migration between the source and the sink on the membrane surface may be regulated by both membrane electrostatics and compounds that affect interfacial water structure. This work was supported by Grant P25981 from the Austrian Science Fund (FWF) to P.P. 1. Springer, A., V. Hagen, D. A. Cherepanov, Y. N. Antonenko, and P. Pohl. 2011. Proc Natl Acad Sci U S A 108:14461-14466. 2. Zhang, C., ⋯, P. Pohl. 2012. Proc Natl Acad Sci U S A 109:9744-9749.

Foraging patterns of soil springtails are impacted by food resources

Movement of soil microarthropods associated to searching or foraging behaviour has received scanty attention and remained largely unexplored. However, rare studies on soil Collembola suggested that their exploratory behaviour is an important feature of population dynamics. In the current study based on a microcosm experiment, we tested the influence of food sources tied to a distant patch on the foraging behaviour of springtails. The microcosms consisted of five separate 5cm sections bound together. Only the last part of the microcosms (section 5) differentiated the three treatments with no food (C), microflora (M) or microflora+plant (M+P). Collembola were introduced into the first section. The mean covered distance of total collembolan differed between all the treatments. It continuously increased from 0.9 (±0.3)cm in C through 4.7 (±1.0)cm in M to 7.4 (±1.2)cm within M+P. Concomitantly, the mean covered distance was also influenced by the factor “life-form” with on average 7.3cm covered by the epedaphic species which was 73.8% more than hemiedaphic and 82.5% more than euedaphic. Even if differences between life-forms were detected, our results also revealed differences of exploratory pattern between species belonging to the same life-form. Our study clearly shows that springtails are reactive to the quality of their environment, in particular food sources.

Economic Foraging at a Distance Is Not a Question Of If but When: A Response to Grimstead

AbstractGrimstead (2010) develops a transport model that appears to demonstrate that distant patch hunting is energetically efficient at distances of well over 350 km. However, a close examination of her assumptions raises questions concerning the validity of her approach. Here, we examine the effects of using more ecologically justifiable parameters and consider the cost of time spent away from camp on her model’s outcomes. We find that under revised constraints the model yields much shorter maximum transport distances and argue, therefore, that distant patch hunting may be calorically economical in some cases, but not in others.

MOVEMENT OF FORAGING TUNDRA SWANS EXPLAINED BY SPATIAL PATTERN IN CRYPTIC FOOD DENSITIES

We tested whether Tundra Swans use information on the spatial distribution of cryptic food items (below ground Sago pondweed tubers) to shape their movement paths. In a continuous environment, swans create their own food patches by digging craters, which they exploit in several feeding bouts. Series of short (<1 m) intra-patch movements alternate with longer inter-patch movements (>1 m). Tuber biomass densities showed a positive spatial auto-correlation at a short distance (<3 m), but not at a larger distance (3-8 m). Based on the spatial pattern of the food distribution (which is assumed to be pre-harvest information for the swan) and the energy costs and benefits for different food densities at various distances, we calculated the optimal length of an inter-patch movement. A swan that moves to the patch with the highest gain rate was predicted to move to the adjacent patch (at 1 m) if the food density in the current patch had been high (>25 g/m2) and to a more distant patch (at 7-8 m) if the food density in the current patch had been low (<25 g/m2). This prediction was tested by measuring the response of swans to manipulated tuber densities. In accordance with our predictions, swans moved a long distance (>3 m) from a low-density patch and a short distance (<3 m) from a high-density patch. The quantitative agreement between prediction and observation was greater for swans feeding in pairs than for solitary swans. The result of this movement strategy is that swans visit high-density patches at a higher frequency than on offer and, consequently, achieve a 38% higher long-term gain rate. Swans also take advantage of spatial variance in food abundance by regulating the time in patches, staying longer and consuming more food from rich than from poor patches. We can conclude that the shape of the foraging path is a reflection of the spatial pattern in the distribution of tuber densities and can be understood from an optimal foraging perspective.

Image Structure at the Center of Gaze during Free Viewing

It is generally believed that the visual system is adapted to the statistics of the visual world. Measuring and understanding these statistics require precise knowledge of the structure of the signals reaching fovea during image scanning. However, despite the fact that eye movements cause retinal stimulation to change several times in a second, it is implicitly assumed that images are sampled uniformly during natural viewing. By analyzing the eye movements of three rhesus monkeys freely viewing natural scenes, we report here significant anisotropy in stimulus statistics at the center of gaze. We find that fixation on an image patch is more likely to be followed by a saccade to a nearby patch of similar orientation structure or by a saccade to a more distant patch of largely dissimilar orientation structure. Furthermore, we show that orientation-selective neurons in the primary visual cortex (V1) can take advantage of eye movement statistics to selectively improve their discrimination performance.

Spontaneous CSF leak treated with percutaneous CT-guided fibrin glue

Gladstone et al.1 advocate sealing CSF leaks with CT-guided, targeted fibrin glue injections in patients with spontaneous intracranial hypotension (SIH). We agree that the injection should be made at the site of the leak as a distant epidural blood patch may often give only temporary relief. In our SIH patients, we obtained permanent sealing of the leak in 13 of 16 cases in which the CSF loss at a spinal root level was approached either by direct surgery (three successful cases) or by targeted percutaneous …

Movements of frugivorous birds among fragmented rainforests in the Northern Territory, Australia

Rainforests in the Northern Territory occur as small patches, and the frugivorous birds that depend on them are thought to move among the patches. I attached radio-transmitters to 41 birds of four species captured in several locations near Darwin. I recorded 55 interpatch flights, and estimated flight rates as between once per day and five days for figbirds and pied imperial-pigeons. The flight rates for rose-crowned fruit-doves and yellow orioles were much lower, but no reliable estimate could be made. The median flight distance was 2.5 km but one in five flights were more than 10 km. In addition, one pigeon flew 220 km in preparation for migration from Australia. Birds often undertook exploratory flights, returning to the original patch. Birds of one species captured together usually flew to different locations. When birds left a patch, it was usually to a distant patch, rather than a near neighbour. These movement patterns demonstrate that frugivorous birds use the rainforest network in a complex way. The birds depend on a network of rainforest patches and the pigeons and figbirds probably disperse large quantities of seeds among the patches. The conservation of rainforest ecosystems in northern Australia will depend on the protection of the current configuration of patches rather than a representative set of patches.

Colonization and Connectivity of Habitat Patches for Coastal Marine Species Distant from Source Populations

Abstract:The exchange of propagules or mobile adults between isolated habitat patches is of critical importance for some types of preserves, especially for species that cannot propagate locally. In the marine realm, the role of planktonic dispersal in maintaining viable local populations can be tested by examining life‐history traits of species that colonize ( or do not colonize ) isolated habitat patches. We compared the abundances of benthic species on an exposed rocky jetty surrounded by dissimilar habitats on the coast of Washington ( U.S.A. ) with those of species at distant bedrock sites within potential source areas. Despite its isolation, the jetty lacked only a small proportion of the potential algal species; these absences could result from the 40‐ to 100‐km distances to larger source areas or from subtle habitat differences at the jetty. Coralline algae are expected to be poor dispersers, both because propagules are short‐lived and because adults are unlikely to float. These algae were absent on the study jetty, although they occur on other isolated jetties on this coast. Short‐term transplant experiments indicated that corallines can survive locally once they colonize. Few animals were absent; one was a chiton that settles and feeds on coralline algae. Animals with obligate dispersal of offspring were abundant on the jetty despite their inability to propagate locally and despite dilution of larvae dispersing in the plankton from distant sources. Conversely, some animal species with no planktonic phase were also present; thus, organisms with a wide range of life‐history traits can persist at this distant and small patch of suitable habitat. Isolation along this shoreline did not eliminate either poor dispersers or obligate dispersers.

Selective Transport of Animal Parts by Ancient Hunters: A New Statistical Method and an Application to the Emeryville Shellmound Fauna

When deciding which parts of a prey animal to transport home, hunters may be more or less selective. In our vocabulary, unselective hunters are those who usually bring home most of the carcass; selective hunters are those who usually abandon all but the choicest (and/or lightest) parts. This paper uses the abcml statistical method to develop a means of estimating transport selectivity from the frequencies of skeletal parts in a faunal assemblage. It then applies the method to artiodactyl data from the Emeryville Shellmound in order to test the local depression and distant patch use hypothesis. This hypothesis predicts that selectivity should decline during the early part of the Emeryville sequence and rise during the later part. The initial analysis did reveal such a pattern, but this pattern disappeared when samples were pooled in order to produce acceptably narrow confidence intervals. Although this result weakens the hypothesis, it does not firmly refute it, because the model fits the data imperfectly in the critical middle portion of the sequence. Abcml also provides estimates of the intensity of attrition, which indicate that attrition was most severe in early strata and least severe in later ones. Substantial attrition (50% of bones surviving) is indicated even from samples that show no indication of attrition using conventional methods. These conclusions are based on assumptions about the processes of transport and attrition that are more reliable in qualitative outline than in quantitative detail. Consequently, the paper's qualitative conclusions are more trustworthy than its quantitative estimates.

Long‐Distance Dispersal and Colonization in the Bay Checkerspot Butterfly, Euphydryas Editha Bayensis

Dispersal, patch finding, and colonization abilities of the Bay checkerspot butterfly (Euphydryas editha bayensis) were measured in field experiments. Butterflies released in non—habitat were capable of moving several kilometres to reach a distant habitat patch. However, their interhabitat movements appeared to be non—oriented, unless they were within 50 m of a suitable patch. To quantify colonization ability, I transplanted propagules of 100 postdiapause larvae each to 38 vacant habitats. Twenty—four transplants (63%) produced adults in the initial year, and 6(25%) of these initially successful transplants persisted to produce adults one year later. Thus the chances of successful population establishment, given the presence of gravid female on a vacant habitat, appear to be low (i.e., at most a 6.25% chance of persisting 2 yr). The present distribution of the butterfly suggests that hilly intervening terrain inhibits the colonization of distant habitat patches. These results shed additional light upon the dynamics of a metapopulation of the Bay checkerspot butterfly.