Niche dynamics of shorebirds in Delaware Bay: Foraging behavior,habitat choice and migration timing

Niche differentiation through resource partitioning is seen as one of the most important mechanisms of diversity maintenance contributing to stable coexistence of different species within communities. In this study, I examined whether four species of migrating shorebirds, dunlins (Calidris alpina), semipalmated sandpipers (Calidris pusilla), least sandpipers (Calidris minutilla) and short-billed dowitchers (Limnodromus griseus), segregate by time of passage, habitat use and foraging behavior at their major stopover in Delaware Bay during spring migration. I tested the prediction that most of the separation between morphologically similar species will be achieved by differential migration timing. Despite the high level of overlap along observed niche dimensions, this study demonstrates a certain level of ecological separation between migrating shorebirds. The results of analyses suggest that differential timing of spring migration might be the most important dimension along which shorebird species segregate while at stopover in Delaware Bay. Besides differences in time of passage, species exhibited differences in habitat use, particularly least sandpipers that foraged in vegetated areas of tidal marshes more frequently than other species, as well as short-billed dowitchers that foraged in deeper water more often than small sandpipers did. Partitioning along foraging techniques was less prominent than segregation along temporal or microhabitat dimensions. Such ranking of niche dimensions emphasizes significance of temporal segregation of migratory species – separation of species by time of passage may reduce the opportunity for interspecific aggressive encounters, which in turn can have positive effects on birds' time and energy budget during stopover period.     

Atmospheric trajectories and spring bird migration across the Gulf of Mexico

We examined the relationship between the longitude of peak arrival of trans-Gulf migrants on the northern coast of the Gulf of Mexico in spring and wind trajectories over the Gulf at three different altitudes (500, 1,500, and 2,500 m above ground level). We used data from 10 WSR-88D radars (weather surveillance radar-1988-Doppler) from Brownsville, Texas, to Key West, Florida, to record the time and longitude of peak arrival on the northern Gulf coast for four spring migrations (2001–2004). We used the National Oceanic Atmospheric Administration Air Resources Laboratory HYSPLIT transport and dispersion model at the READY Web site to generate backward, 24-h atmospheric trajectories based on archived atmospheric data for each trans-Gulf flight. The trajectories began at the geographic location where radar indicated the greatest concentrations of arriving migrants. Although the longitude of peak arrival varied, peak densities of most trans-Gulf migrants arrived on the northern coast near longitude 95°W. Regression analyses showed that the relationship between the longitude of peak trans-Gulf arrival and the direction of atmospheric trajectory was significant but weak at the 500-m level, where few migrants occurred, and was insignificant for the 1,500- and 2,500-m altitudes, where migrant densities were greater. We conclude that winds aloft over the Gulf have little influence on the longitude of peak trans-Gulf arrival on the northern coast of the Gulf of Mexico, and we speculate that the arrival pattern may reflect the trans-Gulf migration pathways that evolved during the Last Glacial Maximum.     

Trends in water quality and discharge confound long-term warming effects on river macroinvertebrates

1. Climate‐change effects on rivers and streams might interact with other pressures, such as pollution, but long‐term investigations are scarce. We assessed trends among macroinvertebrates in 50 southern English streams in relation to temperature, discharge and water quality over 18 years (1989–2007). 2. Long‐term records, coupled with estimates from inter‐site calibrations of 3–4 years, showed that mean stream temperatures in the study area had increased by 2.1–2.9 °C in winter and 1.1–1.5 °C in summer over the 26 year period from 1980 to 2006, with trends in winter strongest. 3. While invertebrate assemblages in surface‐fed streams were constant, those in chalk‐streams changed significantly during 1989–2007. Invertebrate trends correlated significantly with temperature, but effects were spurious because (i) assemblages gained taxa typical of faster flow or well‐oxygenated conditions, contrary to expectations from warming; (ii) more invertebrate families increased in abundance than declined and (iii) concomitant changes in water quality (e.g. declining orthophosphate, ammonia and biochemical oxygen demand), or at some sites changes in discharge, explained more variation in invertebrate abundance and composition than did temperature. 4. These patterns were reconfirmed in both group‐ and site‐specific analyses. 5. We conclude that recent winter‐biased warming in southern English chalk‐streams has been insufficient to affect invertebrates negatively over a period of improving water quality. This implies that positive management can minimize some climate‐change impacts on stream ecosystems. Chalk‐stream invertebrates are sensitive, nevertheless, to variations in discharge, and detectable changes could occur if climate change alters flow pattern. 6. Because climatic trends now characterize many inter‐annual time‐series, we caution other investigators to examine whether putative effects on ecological systems are real or linked spuriously to other causes of change.     

The estimation of population size,migration rates and survival in a stratified population

Summary Estimates of survival, migration rates, and population size are developed for a triple catch marking experiment onn (n>-2) areas with migration among all areas and death in all areas occurring, but no recruitment (birth). This repressents the extension to three sampling times of the method ofChapman andJunge (1956) for estimates in a stratified population. The method is further extented to allow for ‘losses on capture’.     

The diffusion model for migration and selection in a dioecious population

The diffusion approximation is derived for migration and selection at a multiallelic locus in a dioecious population subdivided into a lattice of panmictic colonies. Generations are discrete and nonoverlapping; autosomal and X-linked loci are analyzed. The relation between juvenile and adult subpopulation numbers is very general and includes both soft and hard selection; the zygotic sex ratio is the same in every colony. All the results hold for both adult and juvenile migration. If ploidy-weighted average selection, drift, and diffusion coefficients are used, then the ploidy-weighted average allelic frequencies satisfy the corresponding partial differential equation for a monoecious population. The boundary conditions and the unidimensional transition conditions for coincident discontinuities in the carrying capacity and migration rate extend identically. The previous unidimensional formulation and analysis of symmetric, nearest-neighbor migration of a monoecious population across a geographical barrier is generalized to symmetric migration of arbitrary finite range, and the transition conditions are shown to hold for a dioecious population. Thus, the entire theory of clines and of the wave of advance of favorable alleles is applicable to dioecious populations.This work was supported by National Science Foundation grant BSR-9006285     

Density-dependent migration and human population structure in historical Massachusetts

Studies of population structure often focus on the effects of population size and migration rates on genetic variation. Few studies, however, have investigated the relationship between these two factors. The purpose of this paper is to determine the extent to which migration (and gene flow) is density-dependent (that is, affected by population size) for populations in historical Massachusetts. Data from 4,859 marriage records were analyzed from four populations in north-central Massachusetts during the time period 1741 to 1849. These data were placed into 29 samples defined in terms of population and time cohort. Within each cohort the overall exogamy rate was computed along with three estimates of gene flow based on marital migration: local migration (k), long-distance migration (m), and effective migration rate (me). Three samples show unusually low rates that reflect the history of settlement. Regression analyses were used with the remaining samples, and they show nonlinear density-dependent migration that is unrelated to temporal trends. Migration is highest in samples with small population sizes (less than 800) and large population sizes (greater than 1,600). Migration is lowest in medium-sized populations. Two processes are suggested to explain this curvilinear relationship of migration and population size. In small populations, the lack of suitable potential mates and/or availability of settled land leads to an increase in migration into the population. As population size increases, this migration decreases. After populations reach a certain size, migration increases again, most likely reflecting the economic pull of larger populations. These patterns could act to enhance, or counter, genetic drift, depending on the direction of density dependence.     

Fuel load and flight ranges northern Iberia during autumn of blackcaps Sylvia atricapilla in and spring migrations

Fuel accumulation, mainly as fatty acids, is one of the main characteristics of migratory, birds. Studying to what extent each population or species manages fuel load and how it varies along routes of migration or between seasons （autumn and spring migrations） is crucial to our understanding of bird migration strategies. Our aim here was to analyse whether migratory blackcaps Sylvia atrieapilla passing through northern Iberia differ in their mean fuel loads, rate of fuel accumulation and ＇ potential＇ flight ranges between migration seasons. Blackcaps were mist netted for 4 h-periods beginning at dawn from 16 September to 15 November 2003 - 2005, and from 1 March to 30 April 2004 - 2006 in a European Atlantic hedgerow at Loza, northern Iberia. Both fuel load and fuel deposition rate （this latter assessed with difference in body mass of within-season recaptured individuals） were higher in autumn than in spring. Possible hypotheses explaining these results could be seasonal-associated variations in food availability （likely lower during spring than during autumn）, the fact that a fraction of the migrants captured in spring could breed close to the study area and different selective pressures for breeding and wintering     

Cross-cultural analysis of migration rates: effects of geographic distance and population size.

A model is developed that treats migration rates among populations as a function of the geographic distance between them and the size of both sources and recipient population. Specifically, mij/mjj = a(Ni/Nj)pe-bd, where mij/mjj is the relative migration rate into population j from population i, Ni is the size of the source population, Nj is the size of the recipient population, d is the geographic distance between populations i and j, p is a measure of differential density-dependence, b is a measure of distance decay, and a is an adjustment parameter with little demographic meaning. Methods of parameter estimation and hypothesis testing using maximum likelihood are outlined. These methods are applied to migration matrix data from 13 samples obtained from the literature representing a wide range of ecological settings. All samples show a significant effect of geographic distance on migration, and all but one show a significant effect of differential population size. All but one sample show an overall tendency for migration to be negative density-dependent; that is, the relative migration rate is greater from larger populations to smaller populations than the reverse.     

Effects of dispersal,population delays,and forest fragmentation on tree migration rates

Examining the relation between the dispersal of seeds across landscapes and the migration of species can inform studies of processes such as invasions and response to climatic change. In this research a spatially explicit model is used to analyze the effects of dispersal probability, limits on establishment, generation time, seed crop probability, and varying proportions and patterns of landscape fragmentation on migration rate. Comparisons are made with rates inferred for migrations based on isopols of species range changes in the Holocene (20–200 km/century). The effects of the parameters on migration rate in the model are additive. Dispersal probability, related to diaspore type, is the most influential factor. Limits on establishment show effects only if severe. Lower seed crop probabilities can slow migration slightly. Generation times of 10 to 40 yr reduce migration rate moderately, while generations set long enough to reflect population doubling times would slow migration greatly. Extensive fine-scale fragmentation slows migration more than a single large barrier, but not greatly; multiple large barriers have greater effects. The factors have their greatest absolute and relative effects at higher dispersal probabilities; this result indicates that combinations of low dispersal probability and slow population development could increase the differences in migration rate among species while fragmentation could reduce these differences.     

The diffusion model for migration and selection in a plant population

 The diffusion approximation is derived for migration and selection at a multiallelic locus in a partially selfing plant population subdivided into a lattice of colonies. Generations are discrete and nonoverlapping; both pollen and seeds disperse. In the diffusion limit, the genotypic frequencies at each point are those determined at equilibrium by the local rate of selfing and allelic frequencies. If the drift and diffusion coefficients are taken as the appropriate linear combination of the corresponding coefficients for pollen and seeds, then the migration terms in the partial differential equation for the allelic frequencies have the standard form for a monoecious animal population. The selection term describes selection on the local genotypic frequencies. The boundary conditions and the unidimensional transition conditions for a geographical barrier and for coincident discontinuities in the carrying capacity and migration rate have the standard form. In the diallelic case, reparametrization renders the entire theory of clines and of the wave of advance of favorable alleles directly applicable to plant populations. Received 30 August 1995; received in revised form 23 February 1996     

Inter-annual variations of leaf-fall phenology and leaf-litter nitrogen concentration in a hinoki cypress (<Emphasis Type="Italic">Chamaecyparis obtusa</Emphasis> Endlicher) stand

Inter-annual variations in leaf-fall phenology and leaf-litter nitrogen concentration were investigated for 13 years in a coniferous plantation of hinoki cypress trees (Chamaecyparis obtusa Endlicher) in Kochi, southern Japan. Mean annual nitrogen concentration in the leaf litter ranged from 5.97 to 7.12 g kg⁻¹. The removal of 30 percent of the trees’ basal area in the 3rd year had little effect on leaf-litter nitrogen concentration. The nitrogen concentration in the leaf litter was not correlated with the mean temperature from March to October. The leaf-fall duration, i.e., time between 10 and 90% of the annual leaf fall, was shorter and the leaf-litter nitrogen concentration was lower when the solar radiation from March to October was higher. The results suggest that the hinoki trees shed their leaves abruptly and have lower leaf-litter nitrogen concentration when the solar radiation is higher and that effects of temperature on leaf-fall properties may not be strong in warm climate areas.     

Position and time specify the migration of a pioneering population of olfactory bulb interneurons

We defined the cellular mechanisms for genesis, migration, and differentiation of the initial population of olfactory bulb (OB) interneurons. This cohort of early generated cells, many of which become postmitotic on embryonic day (E) 14.5, differentiates into a wide range of mature OB interneurons by postnatal day (P) 21, and a substantial number remains in the OB at P60. Their precursors autonomously acquire a distinct identity defined by their position in the lateral ganglionic eminence (LGE). The progeny migrate selectively to the OB rudiment in a pathway that presages the rostral migratory stream. After arriving in the OB rudiment, these early generated cells acquire cellular and molecular hallmarks of OB interneurons. Other precursors--including those from the medial ganglionic eminence (MGE) and OB--fail to generate neuroblasts with similar migratory capacity when transplanted to the LGE. The positional identity and migratory specificity of the LGE precursors is rigidly established between E12.5 and E14.5. Thus, the pioneering population of OB interneurons is generated from spatially and temporally determined LGE precursors whose progeny uniquely recognize a distinct migratory trajectory.     

Stochastic growth and extinction in a spatial geometric Brownian population model with migration and correlated noise

A continuous spatial model for populations that are not density-regulated is analyzed. The model is a generalization of the geometric Brownian motion often used to describe populations at a single location. The locations are linked by migration and spatial correlation in the noise. At any point of time, the population size at a given location is log normally distributed so the log population size constitutes a Gaussian field. The model is homogeneous in space but not in time. In particular, we analyze the case when the stochastic growth rate is negative and the total population approaches extinction. The properties of the extinction process is studied by considering local quasi-extinctions. A major conclusion is that migration tends to increase the time to extinction provided that there is no cost of migration. However, as the area occupied by the species starts to decrease, the decrease is faster for populations with larger migration.     

Isotopic tracking of foraging and long-distance migration in northeastern Pacific pinnipeds

We investigated the impact of foraging location (nearshore vs offshore) and foraging latitude (high vs middle) on the carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope compositions of bone collagen of northern fur seals (Callorhinus ursinus), harbor seals (Phoca vitulina), California sea lions (Zalophus californianus), and northern elephant seals (Mirounga angustirostris). Nearshore-foraging harbor seals from California had δ¹³C values 2.0‰ higher than female northern elephant seals foraging offshore at similar latitudes. Likewise, nearshore-foraging harbor seals from Alaska had values 1.7‰ higher than male northern fur seals, which forage offshore at high latitudes. Middle-latitude pinnipeds foraging in either the nearshore or offshore were ¹³C enriched by ∼1.0‰ over similar populations from high latitudes. Male northern elephant seals migrate between middle and high latitudes, but they had δ¹³C values similar to high-latitude, nearshore foragers. Female northern fur seal δ¹³C values were intermediate between those of high- and middle-latitude offshore foragers, reflecting their migration between high- and middle-latitude waters. The δ¹³C values of California sea lions were intermediate between nearshore- and offshore-foraging pinnipeds at middle latitudes, yet there was no observational support for the suggestion that they use offshore food webs. We suggest that their “intermediate” values reflect migration between highly productive and less-productive, nearshore ecosystems on the Pacific coasts of California and Mexico. The relative uniformity among all of these pinnipeds in δ¹⁵N values, which are strongly sensitive to trophic level, reveals that the carbon isotope patterns result from differences in the δ¹³C of organic carbon at the base of the food web, rather than differences in trophic structure, among these regions. Finally, the magnitude and direction of the observed nearshore-offshore and high-to middle-latitude differences in δ¹³C values suggest that these gradients may chiefly reflect differences in rates and magnitudes of phytoplankton production as well as the δ¹³C value of inorganic carbon available for photosynthesis, rather than the input of ¹³C-enriched macroalgal carbon to nearshore food webs. Received: 8 September 1998 / Accepted: 24 February 1999     

Variation in flight duration among individual Tetraopes beetles: Implications for studies of insect flight

Milkweed beetles, Tetraopes tetraophalmus (Forster) (Cerambycidae), were flight tested three times weekly throughout their lives. Flight durations peaked early in life and then declined rapidly with age. Significant variation existed (1) between individuals, with some flying for long periods of time, others for only a few seconds, and (2) within individuals, with some flying for long periods on some test days and very briefly or not at all on other days. Long and short fliers were indistinguishable on the basis of size, sex, or lifespan. The data show that studies of insect flight will underestimate the number of long fliers in a population by as much as 50% or more unless individuals are flight tested more than once.     

Lung cancer and matrix metalloproteinases inhibitors of polyphenols from Selaginella tamariscina with suppression activity of migration

Cancer metastasis has been a major impediment to effective cancer treatment and is the major cause of cancer-related death. Polyphenols compounds have been reported to possess anti-metastasis activity through their inhibitory activity of matrix metalloproteinases (MMPs). In this paper, twelve polyphenols compounds, including three novel phenols, named selaphenins A–C (1–3), two known selaginellin derivatives (4 and 5), together with seven known biflavonoids (6–12) were isolated from the plant of Selaginella tamariscina. Their structures were elucidated by extensive spectroscopic analyses. Notably, polyphenols compound 10 suppressed the migration of A549 cells by primary targeting MMP-9. The antitumor activity of compound 10 was possibly due to the induction of cell apoptosis through intrinsic apoptosis pathways, accompanied by increasing the expression of Bax and caspase-3 in a dose-dependent manner. This study provides evidence that polyphenols analogues from S. tamariscina as inhibitors of MMP-9 exhibited potential migration inhibition activities.     

The effect of migration on metapopulation stability is qualitatively unaffected by demographic and spatial heterogeneity

Coupled map lattices (CMLs), using two coupled logistic equations, have been extensively used to model the dynamics of two-patch ecological systems. Such studies have revealed that migration rate plays an important role in determining the dynamics of the system, particularly when the two maps differ in their intrinsic growth rate parameter, r. However, under more realistic assumptions, a metapopulation can be expected to consist of more than two subpopulations, each with its own demographic parameters, which will in part be a function of the environment of that patch. The role of the spatial arrangement of heterogeneous (i.e. with different r values) subpopulations in shaping the dynamics of such a metapopulation has rarely been investigated. Here, we study the effect of demographic and spatial heterogeneity on the stability of one- and two-dimensional systems of 64 coupled Ricker maps with different r values, under periodic and absorbing boundary conditions. We show that the effects of migration rate on metapopulation stability do not depend upon either the precise spatial arrangement of the subpopulations in the lattice, or on the presence of a moderate proportion of vacant (uninhabitable) patches in the lattice. The results, thus, suggest that metapopulation models are robust to variation in spatial arrangement of patch quality and, hence, of demographic parameters. We also show that for any given arrangement of the patches, maximum stability of the metapopulation occurs when the migration levels are intermediate, a result that agrees well with previous studies on two-map CML systems.