Individualistic responses of bird species to environmental change

We investigated how the population dynamics of the same bird species varied in different environments, and how the population dynamics of different species varied in the same environment, by calculating long-term population trends for 59 insectivorous songbird species in 22 regions or strata of eastern and central North America using data from the North American Breeding Bird Survey. Of the 47 species that occurred in more than one region 77% increased in some regions and declined in others. Of the 22 regions 91% had some species that increased and others that decreased. There were only slightly more significant correlations between strata in species trends and between species for stratum trends than would be expected by chance. Because of nonlinearities in the data, the actual patterns of population fluctuations of the same species in different regions and of different species in the same region were even more heterogeneous than suggested by our analyses of linear trends. We conclude that these bird species respond to spatial and temporal variation in their environment in a very individualistic fashion. These individualistic responses show that the extrapolation of population trends gained from a few local studies to a larger spatial scale, and the use of a few indicator species to monitor the status of a broader community, are suspect.     

Effects of pond size and consequent predator density on two species of tadpoles

Experimental ponds were used as a model system of habitat patches to study the effect of habitat size on the relative growth performance of tadpoles of Bufo americanus and Pseudacris triseriata, and on colonization by predatory insects. Three pond depths and surface areas were habitat size treatments in a replicated, factorial experiment. Tadpoles of both species were astablished together at a single density and ponds were left open to natural colonization by aquatic insects. Pond area had a significant effect on the multivariate response of P. triseriata larval period, survival, and metamorphic mass. P. triseriata survived better relative to B. americanus in larger ponds. However, increasing pond area led to greater incidence of predacious beetle larvae (Dytiscus, Coleoptera: Dytiscidae). Dytiscus larvae had a significant negative effect on the survival of P. triseriata and led to reduced P. triseriata survival relative to B. americanus in colonized ponds. The results suggest that habitat size can influence community structure by altering the distribution of predation among habitat patches.     

Spatial variation in infection by digenetic trematodes in a population of freshwater snails (Potamopyrgus antipodarum)

Larval digenetic trematodes commonly castrate their first intermediate hosts, and should therefore impose strong selection on the timing and mode of host reproduction. Here we examine spatial variation in infection by trematodes in the freshwater snail Potamopyrgus antipodarum. Snails were collected at 11 different sites at Lake Alexandrina on the South Island of New Zealand from transects that ran perpendicular to the shore and across several different habitat types (from 0 to 8 m deep). Logistic regression was used to analyze the relationships between the frequency of trematode infection and snail size, habitat type, and transect location. On average, the probability of infection increased 3.3 times with each 1 mm increase in shell length. Prevalence of infection by the most common species of trematode, Microphallus sp., was highest in the shallow-water habitats where its final hosts (waterflow) spend most of their time. Prevalence of infection by another parasite, Telogaster ophistorchis (final host: eels) increased with depth, but because Microphallus was much more common, total infection by all trematodes decreased with depth. The effects of transect location were minor for Telogaster, but there was significant variation in Microphallus prevalence among transects, especially in the shore-bank habitat. Taken together, these results suggest that the risk of infection is spatially variable, but generally higher in shallow-water habitats, which may explain the greater frequency of sexual individuals as well as earlier reproduction among individuals near shore.     

保护生物学概要

保护生物学的形成是对生物危机的反应和生物科学迅速发展的结果。它是应用科学解决由于人类活动干扰或其它因素引起的物种、群落和生态系统出现的问题的新学科。其”目的是提供保护生物多样性的原理和工具“,其基础科学和应用科学的综合性交叉学科。系统学、生态学、生物地理学和种群生态学的原理和方法是保护生物学重要的理论和实践基础。     

Influence of flood timing on the recovery of macrophytes in a former river channel

Over two vegetation cycles we compared the recovery of macrophytes from flood disturbances that occured at different seasons (July vs December) on patches of a former channel of the Rhône River, France. Some patches were disturbed twice; others were disturbed either in summer or in winter; others were never disturbed and were used as controls.The recovery rate of the vegetation was estimated from the duration of recolonization of the disturbed areas and of growth of the recolonizing species. The influence of the summer disturbance appeared to be strong because the disturbance occurred when the development of the vegetation was maximum. The influence of the winter disturbance was apparently much lower since most species had already declined at this time because of their phenology. The repetition of the two disturbances on the same patch had little influence on the vegetation community.In all cases, the recovery of the vegetation occurred rapidly, both for total vegetation cover and species richness. By the following spring, no significant differences appeared between disturbed and reference patches. The effect of the disturbances varied according to the phenology of the plants, and the macrophyte community studied was more sensitive in summer than in winter.     

River/land ecotones: scales and patterns

On a continental scale a river system itself is an ecotone, mediating between the terrestrial system and the sea. On the landscape scale, ecotones appear between terrestrial and river systems. At decreasing scales, the number and diversity of ecotones increases. Ecotone processes are discussed in relation to the entire river ecosystem, on scales ranging from the activity range of fish fry up to that of adult fish.The introduction of patch theory into the River Continuum Concept (RCC) allows for the proper consideration of hydraulics and time. The relationships between stream order and patch distribution, patch size and lifetime and age diversity of patches are described. This combination model is much better adjusted to the situations occurring in nature than the original, very abstract RCC-model.Dedicated to Professor Franz Berger on the occasion of his 90th birthday     

HARBOR SEAL (PHOCA VITULINA) PREDATION ON SEINED SALMONIDS IN THE LOWER KLAMATH RIVER, CALIFORNIA

Feeding activity of harbor seals ( Phoca vitulina ) was monitored while the California Department of Fish and Game seined and tagged migrating adult salmonids between 1984 and 1988. The number of predations observed each week of observation was significantly correlated with the number of fish seined during that week. There was a significantly higher number of predations observed on days when seining took place than on days when no seining occurred. Our observations suggest that most, if not all, predations we observed on days when seining occurred involved fish that had been recently seined and released. The estimated percentage of seined fish taken by seals was relatively constant over the five years of the study, ranging from 3.1% to 5.5%. Various strategies for reducing the level of predation on seined salmonids in the lower Klamath River are discussed.     

Spectral regions in which aquatic insects see reflected polarized light

For diverse water insects (species of Hydrophilidae, Hadraenidae, Dytiscidae, Haliplidae and aquatic Heteroptera), the attractiveness of an artificial water surface was found to vary when the polarization of the reflected light, the property by which these insects identify water, was abolished in different regions of the spectrum. The sensitivity maxima of their reflection-polarization visual systems (max(POL)) thus determined were in various spectral regions, between < 360 nm (UV) and ca. 550 nm (yellow-green). Species with max(POL) at the short-wavelength end of the spectrum would be able to identify bodies of water by polarization regardless of whether the subsurface reflection was bright or dark; nevertheless, this group includes forms that avoid water with a bright subsurface because of the intensity of the reflected light. Species with max(POL) in the long-wavelength region fail to use certain bodies of water with a bright subsurface as habitats because the light they reflect at the longer wavelengths is insufficiently polarized. That the POL system of a species has a large max could affect habitat choice; on the other hand, it could also be that systems operating in the long-wavelength region were produced in the course of adaptation to the light conditions in or above the habitat.Abbreviations max(POL) spectral sensitivity maximum for polarization vision     

The ecology of ruffe,Gymnocephalus cernuus (Pisces: Percidae) introduced to Mildevatn,western Norway

Synopsis Diet, habitat use, diel and seasonal activity and a number of population parameters were studied on ruffe,Gymnocephalus cernuus, introduced to Mildevatn, western Norway. This lake is sited outside the natural range of the ruffe and has a lower fish diversity and a different fish species composition than within its native range. From June through September the ruffe was planktivorous and mainly caught at 4 to 6 m depth in the benthic zone. At other times of year ruffe was feeding on zoobenthos and caught deeper in the benthic zone. Ruffe was mainly day active. Zooplankton feeding during summer is the clearest difference compared to ruffe populations living within its natural range. Presence of large zooplankton organisms available for ruffe is suggested as the main reason for the difference found in food choice. The availability of large zooplankton is probably due to community structure caused by a predator and lack of interspecific competition for zooplankton in the deeper parts of the lake. Piscivorous brown trout.Salmo trutta, restrict the habitat of threespined stickleback,Gasterosteus aculeatus, to the zone of littoral vegetation, allowing high densities of larger zooplankton species likeBythotrephes longimanus to be present in the lake. Brown trout is present only in the upper light and well oxygenated parts of the lake, leaving a refuge for the ruffe, where they can feed on the rich zooplankton community.     

Hydrologic,vegetation, and substrate characteristics of floating marshes in sediment-rich wetlands of the Mississippi river delta plain,Louisiana, USA

Floating marshes occur over 70% of the western Terrebonne Basin, Louisiana, USA, freshwater coastal wetlands. They are of several types: A free-floating thick-mat (45–60 cm) marsh dominated by Panicum hemitomon and Sagittaria lancifolia; a thick mat marsh dominated by Panicum hemitomon and Sagittaria lancifolia that floats part of the year, but whose vertical floating range is damped compared to adjacent water; and an irregularly-floating thin mat (< 30 cm) dominated by Eleocharis spp. in the spring and Ludwigia leptocarpa and Bidens laevis in the summer and fall. Floating mats must be almost entirely organic in order to be buoyant enough to float. The western Terrebonne wetlands receive large winter/spring supplies of suspended sediments from the Atchafalaya River. Even though sediment concentrations in the adjacent bayou are as high as 100 mg l^–1, the Panicum hemitomon/Sagittaria lancifolia free-floating marsh probably receives no over-surface sediments since it floats continuously. The bulk density data of the damped-floating marsh, however, suggest some mineral sediment input, probably during winter when this marsh is submerged. These two types of floating marsh could not have developed in the present sediment regime of the Atchafalaya River, but as long as they remain floating can continue to exist. Thin floating mats are found in areas receiving the least sediment (<20 mg 1^–1 suspended sediment concentration in adjacent bayous). This low sediment environment probably made possible their formation within the past 20 years. They may represent a transitional stage in mat succession from (1) existing thick-mat floating marsh to a degrading floating marsh, or (2) a floating marsh developing in shallow open water.Corresponding editor: D. Whigham