A demographic analysis of vole population responses to fragmentation and destruction of habitat

 Fragmentation and destruction of natural habitats is currently considered to be the major threat to wildlife populations. We here perform a comprehensive analysis of the demographic effects of habitat fragmentation and destruction on 14 populations of the root vole. The experiment was divided into two consecutive periods. During the first period, we contrasted populations with the same initial size and structure in continuous and fragmented habitat. During the second period, we fragmented the continuous habitat into the same configuration as the permanently fragmented habitat so that the effect of habitat destruction could be evaluated. We estimated survival and fecundity parameters and combined them into population projection matrices to evaluate their relative impact on population growth. In the first period of the experiment there was no difference in population growth rate between fragmented and continuous populations, although litter size was significantly higher in the continuous populations. In the second period, we found higher population growth rates in populations that had experienced habitat destruction. By applying the transition matrix model to empirical estimates of demographic parameters, we demonstrate that the difference in population growth rate in the second period of the experiment was the result of a nonsignificant difference in adult survival. Movements out of the habitat patches were significantly lower in populations that had experienced habitat destruction. We conclude that predator-caused mortality of animals moving out of the habitat patches was the main determinant of demographic variation in this system. Received: January 31, 2002 / Accepted: March 25, 2003     

A population model for the black tern Chlidonias niger in West-Europe

Based on empiric data of breeding success and accurate number trends in The Netherlands, a population model for the black tern was constructed. This model is based on Leslie matrices. Reproductive parameters from the four most important landscape types (river landscape, agricultural grasslands, peat marsh and heath land/moors) are used as model input. Highly accurate national population trend data were used to obtain the best (least square) estimate of overall adult and subadult survival (resp. 0.849 and 0.595). Estimating survival parameters in this way might be useful for threatened (bird) species, especially if catching and ringing is difficult or less desired from a conservation perspective. The model shows the actual importance of the river landscape as the main source for reproductive output of the Dutch black tern population. The prediction model was subsequently used to test different conservation strategies for the Dutch black tern population. Conservation strategies ranged from a null scenario (no change in conservation effort) to in- or decreasing the number of rafts in the most productive landscape (river landscape) to a scenario where breeding success is improved recently in agricultural grasslands via minimizing disturbance. For all scenarios, the model predicts a slow to rapid population increase in the Dutch black tern population after 10–20 years. Improving breeding success in agricultural grasslands habitat has the highest added value.     

Importance of adult survival, local recruitment and immigration in a declining boreal forest passerine, the willow tit Parus montanus

Population growth rate (λ) and its components (adult survival, local recruitment, immigration and their relative contributions to λ) were studied in the declining willow tit Parus montanus in Northern Finland. Capture–recapture models for open populations were used to estimate the population parameters and their process variation. Adult survival was fairly high with low variation (0.593, CV=0.067). As expected, local recruitment was lower and more variable (0.063, CV=0.610). During the 12-year study, the population growth rate averaged to one (0.988, CV=0.197; calculated as However, if the present processes continue, population projections show that the population is likely to decline. There was considerable temporal variation in the relative contributions of demographic parameters to λ. In all years, adult survival had the highest relative contribution (mean 64%) to the population growth rate and it was the least variable trait. Immigration had a higher relative contribution (22%) to λ than local recruitment (14%). Based on the results for the contributions to λ, the main conservation concern for willow tits is adult survival. Due to low variation, adult survival may be difficult to enhance, but at least it should be prevented from declining. High stochasticity in local recruitment and immigration is probably an inherent characteristic of highly seasonal environments, making these traits difficult to address for conservation practices.     

Use of space as an indicator of social behavior and breeding systems in the gymnotiform electric fish <Emphasis Type=Italic>Brachyhypopomus pinnicaudatus</Emphasis>

Extreme sexual dimorphism suggests that the South American electric fish, Brachyhypopomus pinnicaudatus Hopkins (Copeia 1991:151–161, 1991) is polygynous. No field studies have been conducted on the social behavior of this common gymnotiform species, in part because their nocturnal habits and densely vegetated habitat precludes direct observation in the field. We conducted mark–recapture studies on B. pinnicaudatus in Uruguay to gather indirect evidence of their breeding system. Sex ratios of adults were highly skewed toward females 2–3 weeks into the breeding season. Females moved twice as far as males on average (p = 0.016) and movement tracks of individual females overlapped one another but those of males did not. These data support the hypothesis that B. pinnicaudatus is polygynous or polygynandrous, and suggest that they use space in a manner consistent with exploded lek polygyny or iteroparous nest site polygynandry models. Fish detected within 2 m of each other were more aggregated than chance, both day and night, suggesting they maintain social groupings or alerting networks.     

Breeding dispersal in a heterogeneous landscape: the influence of habitat and nesting success in greater snow geese

Despite numerous studies on breeding dispersal, it is still unclear how habitat heterogeneity and previous nesting success interact to determine nest-site fidelity at various spatial scales. In this context, we investigated factors affecting breeding dispersal in greater snow geese (Anser caerulescens atlanticus), an Arctic breeding species nesting in two contrasting habitats (wetlands and mesic tundra) with variable pattern of snowmelt at the time of settlement in spring. From 1994 to 2005, we monitored the nesting success and breeding dispersal of individually marked females. We found that snow geese showed a moderate amount of nest-site fidelity and considerable individual variability in dispersal distance over consecutive nesting attempts. This variability can be partly accounted for by the annual timing of snowmelt. Despite this environmental constraint, habitat differences at the colony level consistently affected nesting success and settlement patterns. Females nesting in wetlands had higher nesting success than those nesting in mesic tundra. Moreover, geese responded adaptively to spatial heterogeneity by showing fidelity to their nesting habitat, independently of snowmelt pattern. From year to year, geese were more likely to move from mesic to high-quality wetland habitat, regardless of previous nesting success and without cost on their subsequent nesting performance. The unpredictability of snowmelt and the low cost of changing site apparently favour breeding-site dispersal although habitat quality promotes fidelity at the scale of habitat patches.     

Brucellosis, botflies, and brainworms: the impact of edge habitats on pathogen transmission and species extinction

Ecological interactions between species that prefer different habitat types but come into contact in edge regions at the interfaces between habitat types are modeled via reaction-diffusion systems. The primary sort of interaction described by the models is competition mediated by pathogen transmission. The models are somewhat novel because the spatial domains for the variables describing the population densities of the interacting species overlap but do not coincide. Conditions implying coexistence of the two species or the extinction of one species are derived. The conditions involve the principal eigenvalues of elliptic operators arising from linearizations of the model system around equilibria with only one species present. The conditions for persistence or extinction are made explicit in terms of the parameters of the system and the geometry of the underlying spatial domains via estimates of the principal eigenvalues. The implications of the models with respect to conservation and refuge design are discussed. Received: 10 June 1999 / Revised version: 7 July 2000 / Published online: 20 December 2000     

The Large Blue butterfly, Phengaris [Maculinea] arion, as a conservation umbrella on a landscape scale: The case of the Czech Carpathians

Conservation umbrellas are charismatic species, the conservation of which also conserves the high diversity of associated plants and animals. The Large Blue butterfly, Phengaris [Maculinea] arion (Lepidoptera, Lycaenidae), is a textbook example of a charismatic endangered invertebrate, intensively studied throughout Europe and protected by the EU Habitat Directive. While surveying P. arion at the westernmost outskirts of the Carpathians (Javorniky and Vsetinske Mts.), within a stronghold of the species in the Czech Republic, we asked whether occupied sites differed from unoccupied ones in the composition of vascular plants and butterfly assemblages. The occupied sites (n = 65) were small pastures, including abandoned ones, with S to W exposure, located on rugged terrain and displaying a high microtopographic heterogeneity; the unoccupied sites (n = 101) were typically mown or intensively grazed. The vegetation of occupied sites was characteristic for non-intensive submountain pasture, butterfly assemblages were species richer, contained more specialised species, and significantly higher proportion of red-listed species. P. arion thus may act as an umbrella for a high number of species associated with traditional land use in the study area and elsewhere. Its survival will depend on the continuation of small-scale land use varying in space and time, and can be threatened by uniformisation of management, even if practised under the guise of agri-environmental payments.     

Observations on the relationship between the extracellular changes of taurine and glutamate during cortical spreading depression, during ischemia, and within the area surrounding a thrombotic infarct

Summary. Taurine and glutamate were monitored by microdialysis technique during various cerebral insults: a. Application of K⁺ triggered a cortical spreading depression (CSD). Taurine and glutamate increased concomitantly but recovery of glutamate was faster than that of taurine. b. Application of NMDA induced also CSD but only taurine increased. c. Induction of an infarct triggered repetitive CSDs. Taurine increased rapidly whereas glutamate rose slowly starting with some delay. d. After induction of ischemia, taurine and glutamate increased after onset of depolarisation. The increase of glutamate occurred late after a small, transient increase in parallel with the depolarisation. These data suggest a close functional relationship between the changes of both amino acids. Therefore, they should be monitored together especially in clinical settings: during excitation, only taurine will increase; during overexcitation, taurine will also increase but to a higher maximum followed by a moderate rise of glutamate; after energy failure, taurine will accumulate to its highest level followed by a continuous rise of glutamate. Received January 25, 2000/Accepted January 31, 2000     

Spatial dynamics of supercolonies of the invasive yellow crazy ant, Anoplolepis gracilipes, on Christmas Island, Indian Ocean

Key to the management of invasive species is an understanding of the scope of an invasion, the rate of proliferation and the rate at which invaded habitats become degraded. This study examines the spatial dynamics of high-density supercolonies of the invasive yellow crazy ant, Anoplolepis gracilipes , on Christmas Island, Indian Ocean, and the associated impacts at their boundaries. Since the early 1990s, A. gracilipes supercolonies have occupied over 30% of the 10,000 ha of rainforest on Christmas Island. Thirty-four discrete high-density supercolonies formed between 1989 and 2003, ranging in size across nearly three orders of magnitude from 0.9 to 787 ha. Supercolonies boundaries are diffuse, and ants were observed in low densities in some cases up to 200 m from the main high-density supercolony. The 13 boundaries examined were all dynamic over a 10–20 observation month period: nine boundaries expanded, and the maximum rate of spread was 0.5 m day⁻¹. Across boundary transition zones, between high-density supercolonies and intact rainforest, yellow crazy ants reduced other ant species richness, occupied red crab burrows and killed resident red crabs, which was the trigger for 'invasional meltdown' on Christmas Island. The highly variable and unpredictable nature of A. gracilipes boundaries poses a challenge for incorporation into a predictive framework, as well as for their management.     

Characterization of a novel DNA damage-inducible gene of Saccharomyces cerevisiae , DIN7 , which is a structural homolog of the RAD2 and RAD27 DNA repair genes

A number of DNA damage-inducible genes (DIN) have been identified in Saccharomyces cerevisiae. In the present study we describe isolation of a novel gene, Din7, the expression of which is induced by exposure of cells to UV light, MMS (methyl methanesulfonate) or HU (hydoxyurea). The DNA sequence of DIN7 was determined. By comparison of the predicted Din7 amino acid sequence with those in databases we found that it belongs to a family of proteins which includes S. cerevisiae Rad2 and its Schizosaccharomyces pombe and human homologs Rad13 and XPGC; S. cerevisiae Rad27 and its S. pombe homolog Rad2, and S. pombe Exo I. All these proteins are endowed with DNA nuclease activity and are known to play an important function in DNA repair. The strongest homology to Din7 was found with the Dhs1 protein of S.␣cerevisiae, the function of which is essentially unknown. The expression of the DIN7 gene was studied in detail using a DIN7-lacZ fusion integrated into a chromosome. We show that the expression level of DIN7 rises during meiosis at a time nearly coincident with commitment to recombination. No inducibility of DIN7 was found after treatment with DNA-damaging agents of cells bearing the rad53-21 mutation. Surprisingly, a high basal level of DIN7 expression was found in strains in which the DUN1 gene was inactivated by transposon insertion. We suggest that a form of Dun1 may be a negative regulator of the DIN7 gene expression. Received: 30 May 1996 / Accepted: 26 September 1996     

Population trends and flight behavior of the American burying beetle, Nicrophorus americanus (Coleoptera: Silphidae), on Block Island, RI

The endangered American burying beetle, Nicrophorus americanus, was monitored on Block Island, RI, USA, from 1991–2003 using mark-recapture population estimates of adults collected in pitfall traps. Populations increased through time, especially after 1994 when a program was initiated that provided carrion for beetle production. Beetle captures increased with increasing temperature and dew point, and decreased with increasing wind speed. Short distance movement was not related to wind direction, while longer distance flights tended to be downwind. Although many individuals flew considerable distances along transects, most recaptures were in traps near the point of release. These behaviors probably have counterbalancing effects on population estimates.The U.S. Goverment's right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged.     

The pattern of acropetal and basipetal cytoplasmic streaming velocities in Chara rhizoids and protonemata, and gravity effect on the pattern as measured by laser-Doppler-velocimetry

 The spatial pattern of acropetal and basipetal cytoplasmic streaming velocities has been studied by laser-Doppler-velocimetry (LDV) in the positively gravitropic (downward growing) rhizoids of Chara globularis Thuill. and for the first time in the negatively gravitropic (upward growing) protonemata. The LDV method proved to be precise and yielded reproducible results even when tiny differences in velocities were measured. In the apical parts of the streaming regions of both cell types, acropetal streaming was faster than basipetal streaming. Starting at the apical reversal point of streaming, the velocity increased basipetally with the distance from that point and became fairly constant close to the basal reversal point; subsequently, the velocity decreased slightly acropetally as the apical reversal point was again approached. There was no change in velocity at the basal reversal point. However, at the apical reversal point there was an abrupt decrease in velocity. The pattern of the ratio of acropetal to basipetal streaming velocity (VR) was a function of the relative distance of the site of measurement from the apical reversal point rather than a function of the absolute distance. Upon inversion of the rhizoids, the VR decreased on average by 3.8% (±0.4%), indicating that the effect of gravity on the streaming velocity was merely physical and without a physiological amplification. Rhizoids that had developed on the slowly rotating horizontal axis of a clinostat, and had never experienced a constant gravity vector, were similar to normally grown rhizoids with respect to VR pattern. In protonemata, the VR pattern was not significantly different from that in rhizoids although the direction of growth was inverse. In rhizoids, oryzalin caused the polar organization of the cell to disappear and nullified the differences in streaming velocities, and cytochalasin D decreased the velocity of basipetal streaming slightly more than that of acropetal streaming. Cyclopiazonic acid, known as an inhibitor of the Ca²⁺-ATPase of the endoplasmic reticulum, also reduced the streaming velocities in rhizoids, but had slightly more effect on the acropetal stream. It is possible that the endogenous difference in streaming velocities in both rhizoids and protonemata is caused by differences in the cytoskeletal organization of the opposing streams and/or loading of inhibitors (like Ca²⁺) from the apical/subapical zone into the basipetally streaming endoplasm. Received: 4 October 1999 / Accepted: 4 November 1999     

Evidence for calcification depth change of Globorotalia truncatulinoides between deglaciation and Holocene in the Western Atlantic Ocean

Measurements of the δ¹⁸O in tests of planktonic and benthic foraminifera in the Florida Straits are used to reconstruct the properties of the water column through time over the last 12 ka (Lynch-Stieglitz et al., in press). The isotopic composition of the foraminifera largely reflects the vertical density gradient. We use this reconstruction and δ¹⁸O measurements on Globorotalia truncatulinoides in a nearby core to track the depth habitat of this species from the last deglaciation to 1.6 ka B.P. Around 9 ka, G. truncatulinoides was calcifying in much shallower water than during the late Holocene. The downward migration toward its modern habitat is a regional phenomenon over the western tropical Atlantic continental slope. The cause is still unclear but we hypothesize that the shallower calcification depth may be a response to the presence of glacial melt water or to circulation changes. This study points to the value of further study of the ecology, life cycle and calcification depth for G. truncatulinoides and other planktonic foraminifera that are used to reconstruct the history of the thermocline and upper water column structure.