On the role of patch density and patch variability in central-place foraging

Existing models of the foraging behavior of single-prey loaders in patchy environments differ on whether the optimal forager is predicted to stay in a patch until a prey is found, or to leave a patch for a next one if a prey is not found by a certain “deadline.” This article examines conditions on the probability distribution of prey density across patches that are necessary or sufficient for the existence of a finite, optimal deadline. It is shown that, for environments in which prey density is variable but never falls below some strictly positive level, a finite, optimal deadline exists when and only when the spatial density of patches is “high.” Also, a characterization is given of a large class of distributions (including the gamma distribution) for which a finite, optimal deadline exists for all levels of spatial density of patches.     

The impact of patch encounter rate on patch residence time of female parasitoids increases with patch quality

Abstract.  1. For animal species that forage on patchily distributed resources, patch time allocation is of prime importance to their reproductive success. According to Charnov's marginal value theorem (MVT), the rate of patch encounter should influence negatively the patch residence time: as the rate of patch encounter decreases, the patch residence time increases. Moreover, the MVT predicts that animals should stay longer in high quality patches.
2. Using the aphid parasitoid Aphidius rhopalosiphi (Hymenoptera: Aphidiinae), the effects of these two factors (patch encounter rate and host density) were combined in order to test if the increment in patch residence time for a given decrease in patch encounter rate was larger for high quality patches than for low quality patches.
3. The results show a significant effect of the interaction between the two factors. In high host density patches, parasitoids spent more time if they experienced a low patch encounter rate, while in low host density patches, patch encounter rate had no significant effect on the patch residence time. This suggests that the response of A. rhopalosiphi females to patch encounter rate varied with host density in the patch. Moreover, the same interaction effect was observed for the number of ovipositor contacts on aphids.
4. Parasitoid females can use patch encounter rate to estimate patch density in the habitat but the effect of this estimate on their patch residence time is modulated by patch quality. Staying longer in a patch when patches are rare is more advantageous when the fitness gained by doing so is large. In low quality patches, the expected fitness gain is small and the female may gain more by leaving and taking her chance at finding another patch.     

The structure of the canary's incubation patch

The gross morphology, histology and ultrastructure of the canary's incubation patch and the ventral apterium from which it arises are described. The apterium is vascularized by pectoral, external mammary, incubation, and prepubic arteries. It is innervated by cutaneous branches of spinal nerves. It has a surface area of 6 cm². Its epidermis is a stratified squamous epithelium with basal, intermediate, transitional and cornified layers. Cells in the stratum germinativum contain a normal array of organelles, but are characterized by tonofilaments, desmosomes and interdigitating surfaces. Cellular organelles disappear in the stratum transitivum and are replaced by large vacuoles and keratohyalin bands. Nonmyelinated nerve fibers are abundant in the stratum germinativum. The dermis consists of (1) an avascular layer of dense collagen subjacent to the epidermis and containing many nonmyelinated nerves, and (2) an underlying layer of areolar connective tissue containing blood vessels, lamellar corpuscles and nerves. A layer of coarse elastic fibers, reinforced by collagen and smooth muscle, separates the dermis from subcutaneous tissue. In contrast to the ventral apterium, the incubation patch is featherless and visibly hypervascular and edematous. Its epidermis is both hypertrophic and hyperplastic. Large spaces separate cells in the stratum germinativum. The visible hypervascularity is due to hyperemia and increased number and size of blood vessels in the dermis. Visible edema is due to the accumulation of fluid interstitially. Although no histological differences exist among various regions of the ventral apterium, such differences are present in the incubation patch.     

苦豆子斑块面积及斑块隔离度与豆荚螟发生情况的关联分析

破碎化生态格局中斑块面积和斑块隔离度对生物种群有一定的影响。苦豆子是宁夏荒漠半荒漠地区防风固沙的主要物种,其分布呈现典型的斑块化格局,豆荚螟是其种子的主要害虫。本文在宁夏灵武市宁东镇的余家湖(YJH,6个斑块)和羊场湾(YCW,7个斑块)两个样地共选择了13个苦豆子斑块,采用五点取样法采摘苦豆子豆荚,室内剥检统计害虫数量、豆荚及豆粒的危害率,用单因素方差分析进行差异性检验,用逐步回归法进行斑块面积、斑块隔离度与危害率的关联分析。结果显示:YJH样地斑块平均面积为2 629. 08 m~2,苦豆子平均盖度50. 33%,斑块间豆荚及豆粒危害率差异显著(P 0. 05); YCW样地斑块平均面积为1 010. 34 m~2,苦豆子平均盖度31. 14%,斑块间豆荚豆粒危害率差异不显著(P 0. 05)。13个斑块豆荚及豆粒的危害率均差异显著(P 0. 05)。斑块面积对豆荚螟数量的回归分析显示影响并不显著(R2=0. 084)。两样地间豆粒的危害率并无显著差异(P 0. 05); Pearson相关分析显示斑块连接度指数与豆荚危害率(r=-0. 2215)、豆粒危害率(r=-0. 4102)、豆荚螟数量(r=0. 0561)有一定的相关性。斑块面积对苦豆子种实害虫数量、豆荚及豆粒的危害率影响不显著,但斑块隔离度增加,能够减轻苦豆子种子害虫的危害。     

Estimating the number of channels in patch recordings

The estimation of the number of channels in a patch was assumed to be equivalent to the estimation of the binomial parameter n. Seven estimators were evaluated, using data sets simulated for a range of parameters appropriate for single channel recording experiments. No single estimator was best for all parameters; a combination of estimators is a possible option to avoid the biases of individual estimators. All estimators were highly accurate in estimating n in the case that n = 1. For n ≤ 4 the simplest estimator, the maximum number of simultaneously open channels, was the best, For larger values of n the best estimators were Bayesian.     

Stochastic patch exploitation model

A solitary animal is foraging in a patch consisting of discrete prey items. We develop a stochastic model for the accumulation of gain as a function of elapsed time in the patch. The model is based on the waiting times between subsequent encounters with the prey items. The novelty of the model is in that it renders possible–via parameterization of the waiting time distributions: the incorporation of different foraging situations and patch structures into the gain process. The flexibility of the model is demonstrated with different foraging scenarios. Dependence of gain expectation and variance of the parameters of the waiting times is studied under these conditions. The model allows us to comment upon some of the basic concepts in contemporary foraging theory.     

Roles of DNA ligase III and XRCC1 in regulating the switch between short patch and long patch BER

Damaged DNA bases are repaired by base excision repair (BER), which can proceed via two pathways: short patch and long patch BER. During the latter, a stretch of several nucleotides is replaced by strand displacement DNA synthesis. We recently demonstrated that the ATP concentration may govern the decision between these BER sub-pathways. Employing a reconstituted BER complex containing among others DNA polymerase beta (Pol beta), DNA ligase III (Lig III) and XRCC1, here we show that Lig III and XRCC1 are essential mediators of this regulation. XRCC1 stimulates Pol beta strand displacement activity and releases inhibition of Pol beta by DNA-bound Lig III if ligation is prevented. XRCC1 is thus able to strongly promote strand displacement and long patch BER under conditions of ATP shortage. If sufficient ATP is available, ligation by Lig III prevents strand displacement, leading to short patch BER. Ligation-inactive mutants of Lig III do not prevent strand displacement by Pol beta under the same conditions. Consequently, the preferred use of short patch BER depends on the ligation competence of Lig III. Accordingly, lowering the levels of the XRCC1/Lig III complex in HeLa cells using siRNA decreases ligation capacity but enhances Pol beta-dependent DNA synthesis.     

Optimal patch residence time in egg parasitoids: innate versus learned estimate of patch quality

Charnovs marginal value theorem predicts that female parasitoids should exploit patches of their hosts until their instantaneous rate of fitness gain reaches a marginal value. The consequences of this are that: (1) better patches should be exploited for a longer time; (2) as travel time between patches increases, so does the patch residence time; and (3) all exploited patches should be reduced to the same level of profitability. Patch residence time was measured in an egg parasitoid Anaphes victus (Hymenoptera: Mymaridae) when patch quality and travel time, approximated here as an increased delay between emergence and patch exploitation, varied. As predicted, females stayed longer when patch quality and travel time increased. However, the marginal value of fitness gain when females left the patch increased with patch quality and decreased with travel time. A. victus females appear to base their patch quality estimate on the first patch encountered rather than on a fixed innate estimate, as was shown for another egg parasitoid Trichogramma brassicae. Such a strategy could be optimal when inter-generational variability in patch quality is high and within-generational variability is low.     

Duration of colonization and interactions between early and late colonists determine the effects of patch colonization history on patch biodiversity

Patches can vary in their colonization history as the result of many factors, including differences in patch size and isolation, which alter the timing and duration in which one or more species colonize a patch. Prior work has found that the particular time that a species colonizes a patch can affect the performance of co‐occurring species, but it is less clear whether it affects the biodiversity of the patch. Our objective was to evaluate how two components of colonization history affect biodiversity – the total duration of the colonization window in which a predator is able to colonize the patch and the particular time in the patch's colonization history (i.e. early versus late in community development) that colonization by a predator occurs. We conducted an experiment to examine how the duration and timing in which predatory dragonflies colonize recently filled ephemeral ponds affects insect biodiversity. Dragonfly colonization history had an important effect on insect biodiversity. Ponds with a longer colonization history by dragonflies had fewer insect morphotypes than ponds with a shorter colonization history. The timing of dragonfly colonization (i.e. early versus late in community development) had no effect on the number of insect morphotypes present despite altering both the rate of dragonfly metamorph production and the abundance of larval dragonflies present at the end of the study. The effect of duration of long‐term dragonfly colonization on biodiversity stemmed from early colonists weakening the influence of later colonists on insect biodiversity. Though colonization by dragonflies reduced adult insect abundance, differences in the time in which dragonflies colonized ponds had no effect on total insect abundance. Moreover, differences in patch biodiversity appears to be affected more by variation in the duration a patch was colonized by a predator than variation in the time in which a patch was colonized by a predator.     

Testing the importance of patch scale on forest birds

The relationship between population density and habitat area is of central importance to conservation biology, particularly for species dependent on declining habitat. A recent study by Lee et al. in Oikos in 2002 found that the densities of three forest interior bird species (ovenbirds, wood thrushes, and red-eyed vireos) decline with increasing patch size, contradicting many other studies that demonstrate a positive correlation between area and density for these species. The authors' argument is based on a misapplied criticism of the prevailing approach based on density-and on an inappropriate statistical methodology, caused by incorrect specification of the null hypothesis after log–transformation. We use three different methods of testing area-dependence: a corrected log–abundance log–area regression; a similar abundance–area regression; and the prevailing density-area approach. For each species, all three methods agree broadly, suggesting the robustness of each approach. For ovenbirds and wood thrushes, we do not find that population density is negatively correlated to patch size. While our analyses of the red-eyed vireo data find a negative correlation between the two factors, the strength of the correlation is far weaker than that of Lee et al. and may derive from landscape factors unconsidered in the original data. Nevertheless, we do not find positive density–area relationships for any of these forest-interior species, further underscoring the site-specificity of the underlying mechanisms of area- sensitivity.     

Phytoplankton growth and the microscale nutrient patch hypothesis

It has been hypothesized that phytoplankton in situ grows fasterthan measured nutrient concentrations should allow, and thatmicroscale heterogeneity in nutrient concentration permits phytoplanktonto maintain the elevated growth rates. An examination of literaturedata failed to reveal any significant difference between observedgrowth rates and those predicted from steady-state N-growthkinetics. On the other hand, P kinetics may underestimate growthrates. However, it is demonstrated that a non-homogeneous nutrientsupply regime should actually decrease phytoplankton growthrates, regardless of the physical characteristics of the patches.Patchiness cannot account for elevated phytoplankton growthrates in situ.     

Inhibition of short patch and long patch base excision repair by an oxidized abasic site

5'-(2-Phosphoryl-1,4-dioxobutane) (DOB) is an oxidized abasic lesion that is produced by a variety of DNA damaging agents, including several antitumor antibiotics. DOB efficiently and irreversibly inhibits DNA polymerase β, an essential base excision repair enzyme in mammalian cells. The generality of this mode of inhibition by DOB is supported by the inactivation of DNA polymerase λ, which may serve as a possible backup for DNA polymerase β during abasic site repair. Protein digests suggest that Lys72 and Lys84, which are present in the lyase active site of DNA polymerase β, are modified by DOB. Monoaldehyde analogues of DOB substantiate the importance of the 1,4-dicarbonyl component of DOB for efficient inactivation of Pol β and the contribution of a freely diffusible electrophile liberated from the inhibitor by the enzyme. Inhibition of DNA polymerase β's lyase function is accompanied by inactivation of its DNA polymerase activity as well, which prevents long patch base excision repair of DOB. Overall, DOB is highly refractory to short patch and long patch base excision repair. Its recalcitrance to succumb to repair suggests that DOB is a significant source of the cytotoxicity of DNA damaging agents that produce it.     

The ephemeral resource patch concept

Ephemeral resource patches (ERPs) – short lived resources including dung, carrion, temporary pools, rotting vegetation, decaying wood, and fungi – are found throughout every ecosystem. Their short-lived dynamics greatly enhance ecosystem heterogeneity and have shaped the evolutionary trajectories of a wide range of organisms – from bacteria to insects and amphibians. Despite this, there has been no attempt to distinguish ERPs clearly from other resource types, to identify their shared spatiotemporal characteristics, or to articulate their broad ecological and evolutionary influences on biotic communities. Here, we define ERPs as any distinct consumable resources which (i) are homogeneous (genetically, chemically, or structurally) relative to the surrounding matrix, (ii) host a discrete multitrophic community consisting of species that cannot replicate solely in any of the surrounding matrix, and (iii) cannot maintain a balance between depletion and renewal, which in turn, prevents multiple generations of consumers/users or reaching a community equilibrium. We outline the wide range of ERPs that fit these criteria, propose 12 spatiotemporal characteristics along which ERPs can vary, and synthesise a large body of literature that relates ERP dynamics to ecological and evolutionary theory. We draw this knowledge together and present a new unifying conceptual framework that incorporates how ERPs have shaped the adaptive trajectories of organisms, the structure of ecosystems, and how they can be integrated into biodiversity management and conservation. Future research should focus on how inter- and intra-resource variation occurs in nature – with a particular focus on resource × environment × genotype interactions. This will likely reveal novel adaptive strategies, aid the development of new eco-evolutionary theory, and greatly improve our understanding of the form and function of organisms and ecosystems.