Predator choice in the field; grouping guppies, Poecilia reticulata, receive more attacks

Capture success of many predator species has been shown to decrease with increasing prey group size and it is therefore suggested that predators should choose to attack stragglers and/or small groups. Predator choice in the laboratory has shown mixed results with some species preferentially attacking large groups and others preferring to attack stragglers over groups. Such predator choices have not been tested in the field. In our study we presented a binary choice between a shoal of guppies and a single guppy to predators in pools in the Arima river, Trinidad. We observed attacks in 11 different pools from a total of 53 predators (20 acara cichlids, Aequidens pulcher, 32 pike cichlids, Crenicichla frenata, and one wolf-fish, Hoplias malabaricus) and found that all predators showed a strong preference for the shoal of guppies in terms of both first choice and total number of attacks. We discuss the implications of these preferences with regards to predator–prey interactions.     

The withdrawal of land from mining — A study of the implications for the future

As a result of several decades of growing environmental awareness, pressures to restrict mining activity in areas of high scenic and recreational value are great. The development of planning law, and legislation for National Parks, are outlined as a framework for current mineral policies in this country, which highlight the fact that at present, almost any area in Britain could theoretically be mined, i.e. few areas are actually banned from mineral working. This contrasts with the situation in the USA where considerable acreages, especially in the Western States, are either covered by absolute bans, or are heavily restricted from mining activity.Should some areas of Britain become similarly off-limits to mining, possible implications include increased deficits in the balance of payments, reduced reliability of mineral supplies to industry, adverse social effects on a local scale, and, on the advantageous side, more efficient use of recycled waste and other alternative sources of materials. Taking all these into account, it is concluded that a ban on mining in some areas would be a dangerously short-sighted, inflexible and irreversible step, and a more moderate approach is required, while the need to protect highly valued areas is recognised as being very important.     

Vertical distribution and diurnal migration of some Cyclopoida (Copepoda) in the tropical region of the Pacific Ocean

The material was collected in the western equatorial part of the Pacific Ocean at a 24 h station on December 21 to 23, 1968. Collections were made by means of 2 Juday nets from 2 winches simultaneously. A series of hauls was made at 2 h intervals. The vertical distribution of 17 Cyclopoida species, belonging to 3 families (Oithonidae, Oncaeidae and Corycaeidae) was studied. From 0 to 300 m, the absolute number of Cyclopoida individuals was practically constant throughout the 24 h period. The bulk of the species performed no diurnal vertical migration, or migrated with low intensity in the usual way (i.e. moved upward at night and downward during the day). Only 2 Oncaeidae species performed significant diuranl vertical migration. No reversed migration in Cyclopoida was discovered. To characterize the vertical distribution of Cyclopoida, the distribution of the cores of populations (abundancies between 25 and 75%) was examined. During the 24 h period, the cores of populations of various Cyclopoida species were found at different depths; this steplike distribution was not disturbed in migrating species. The cores of populations differed both with habitat depth and time of ascent of the migrating species to the surface layer. This peculiarity, probably, tends to lessen the intensity of food competition between Cyclopoida species with similar nutritional habits.     

Eine Apparatur zur kontinuierlichen Respirationsmessung an marinen Organismen

Measurements were made with a Clark electrode in a closed system under conditions of different, regulatable water current velocities. Six simultaneous parallel measurements are possible with only one electrode. The volume of respiration chambers amounts to 80 ml for small animals and 300 ml for larger ones. Technical details of the apparatus and measuring procedures are described. The accuracy amounts to 0.5 μl O₂ for the 80 ml chamber, and 2 μl O₂ for the 300 ml chambers. The apparatus has been successfully used on various marine evertebrates and algae.     

The inactive temporary component: an unexplored fraction of meiobenthos

Numerous morphotypes and great abundances of resting stages falling within the meiobenthic size-range were found in meiobenthos samples collected in a coastal lagoon of the North Adriatic Sea. Biodiversity, abundances and energetic values of both active and inactive meiobenthic organisms were analysed by the traditional techniques of meiobenthology. Inactive stages were represented by more than 100 morphotypes and formed 52% of the meiobenthos in terms of numbers of individuals. Inactive meiobenthos came mostly from plankton: the second and third most abundant groups of all meiobenthic organisms were the eggs of a rotifer and the cysts of a dinophyte, respectively. Resting stages of plankters fit the definition of temporary meiobenthos, making up the “inactive temporary meiobenthos”, but they are usually not considered in meiobenthology. The diversity and abundance of the meiobenthos is, thus, currently underestimated; this leads to neglect of the role of meiobenthos in several processes linking different ecosystems. It is hypothesised, for instance, that the meiobenthic resting stages of planktonic organisms (besides being the “seeds” for the perpetuation of planktonic communities) might also be the prey of meiofaunal organisms with piercing mouth parts. If this proves correct, a regulatory role might be proposed for the meiofauna in respect to plankters with benthic stages. Received: 10 September 1998 / Accepted: 12 April 1999     

Assessing Risks to Biodiversity from Future Landscape Change

We examined the impacts of possible future land development patterns on the biodiversity of a landscape. Our landscape data included a remote sensing derived map of the current habitat of the study area and six maps of future habitat distributions resulting from different land development scenarios. Our species data included lists of all bird, mammal, reptile, and amphibian species in the study area, their habitat associations, and area requirements for each. We estimated the area requirements using home ranges, sampled population densities, or genetic area requirements that incorporate dispersal distances. Our measures of biodiversity were species richness and habitat abundance. We calculated habitat abundance in two ways. First, we computed the total habitat area for each species in each landscape. Second, we calculated the number of habitat units for each species in each landscape by dividing the size of each habitat patch in the landscape by the area requirement and summing over all patches. Species richness was based on presence of habitat. Species became extinct in the landscape if they had no habitat area or no habitat units, respectively. We then computed ratios of habitat abundance in each future landscape to habitat abundance in the present for each species. We also computed the ratio of future to present species richness. We then calculated summary statistics across all species. Species richness changed little from present to future. There were distinctly greater risks to habitat abundance in landscapes that extrapolated from present trends or zoning patterns, however, as opposed to landscapes in which land development activities followed more constrained patterns. These results were stable when tested using Monte Carlo simulations and sensitivity tests on the area requirements. We conclude that this methodology can begin to discriminate the effects of potential changes in land development on vertebrate biodiversity.     

Associations of forest bird species richness with housing and landscape patterns across the USA.

In the United States, housing density has substantially increased in and adjacent to forests. Our goal in this study was to identify how housing density and human populations are associated with avian diversity. We compared these associations to those between landscape pattern and avian diversity, and we examined how these associations vary across the conterminous forested United States. Using data from the North American Breeding Bird Survey, the U.S. Census, and the National Land Cover Database, we focused on forest and woodland bird communities and conducted our analysis at multiple levels of model specificity, first using a coarse-thematic resolution (basic models), then using a larger number of fine-thematic resolution variables (refined models). We found that housing development was associated with forest bird species richness in all forested ecoregions of the conterminous United States. However, there were important differences among ecoregions. In the basic models, housing density accounted for < 5% of variance in avian species richness. In refined models, 85% of models included housing density and/or residential land cover as significant variables. The strongest guild response was demonstrated in the Adirondack-New England ecoregion, where 29% of variation in richness of the permanent resident guild was associated with housing density. Model improvements due to regional stratification were most pronounced for cavity nesters and short-distance migrants, suggesting that these guilds may be especially sensitive to regional processes. The varying patterns of association between avian richness and attributes associated with landscape structure suggested that landscape context was an important mediating factor affecting how biodiversity responds to landscape changes. Our analysis suggested that simple, broadly applicable, land use recommendations cannot be derived from our results. Rather, anticipating future avian response to land use intensification (or reversion to native vegetation) has to be conditioned on the current landscape context and the species group of interest. Our results show that housing density and residential land cover were significant predictors of forest bird species richness, and their prediction strengths are likely to increase as development continues.