Effects of Social Structure and Prey Dynamics on Extinction Risk in Gray Wolves

Extinction models based on diffusion theory generally fail to incorporate two important aspects of population biology—social structure and prey dynamics. We include these aspects in an individual-based extinction model for small, isolated populations of the gray wolf (Canis lupus). Our model predicts mean times to extinction significantly longer than those predicted by more general (diffusion) models. According to our model, an isolated population of 50 wolves has a 95% chance of surviving just 9 years and only a 30% chance of surviving beyond 100 years. Reflecting the influence of social structure, a wolf population initially comprising 50 individuals is expected to persist only a few years longer, on average (71 years), than is a population initially comprising just a single reproductive pair (62 years). In contrast, substantially greater average prey abundance leads to dramatically longer expected persistence times. Autocorrelated prey dynamics result in a more complex distribution of extinction times than predicted by many extinction models. We contend that demographic stochasticity may pose the greatest threat to small, isolated wolf populations, although environmental stochasticity and genetic effects may compound this threat. Our work highlights the importance of considering social structure and resource dynamics in the development of population viability analyses.     

Levels and pattern of volatile organic nitrates and halocarbons in the air at Neumayer Station (70 degrees S), Antarctic

Levels and patterns of C1-C4/C9 organic nitrates were measured for the first time in Antarctica. The sampling was done by adsorptive enrichment on Tenax TA followed by thermodesorption cold-trap high resolution capillary gas chromatography with electron capture detection. 2-70 1 air on-column have been analyzed this way. C1-C9 alkyl mononitrates, C2-C4 alkyl dinitrates, C2-C4 hydroxy alkyl nitrates, and halocarbons could be identified in air samples collected near the German Neumayer Research Station, Antarctica, in February 1999. Volatile biogenic and anthropogenic halocarbons were used to assess the origin of the air parcels analyzed. The average concentration measured for sigmaC2-C6 alkyl nitrates was in the range of 9.2 +/- 1.8 ppt(v), while the sum of the mixing ratios of six C2-C4 hydroxy alkyl nitrates was in the range of 1.1 +/- 0.2 ppt(v). Moreover, C2-C4 alkyl dinitrates were found at levels near the detection limit of 0.1-0.5 ppt(v). The concentrations of organic nitrates found in Antarctic air represent ultimate baseline levels due to chemical and physical loss processes during long-range transport in the air. The South Atlantic and the Antarctic Ocean as a general secondary source for organic nitrates in terms of an air/sea exchange equilibrium has to be evaluated yet, but it seems logical. Our results confirm the common assumption that there are no biogenic marine sources of C2-C9 organonitrates. We have found a level of > 80 ppt(v) for methyl nitrate. This level if it can be confirmed in a systematic survey requires a strong biogenic source of methyl nitrate in the Antarctic Ocean.     

Spatially explicit modeling of overstory manipulations in young forests: Effects on stand structure and light

Young forests can be manipulated in diverse ways to enhance their ecological values. We used stem maps from two dense, second-growth stands in western Washington and a spatially explicit light model (tRAYci) to simulate effects of five silvicultural manipulations on diameter distribution, species composition, spatial patterning, and light availability. Each treatment removed 30% of the basal area, but differed in how trees were selected for removal. Three primary treatments were thin from below (removing the smallest trees), random thin (removing trees randomly), and gap creation (removing all trees in circles ∼1 tree height in diameter). Two additional treatments combined elements of these approaches: random ecological thin (a mixture of thin from below and random thin) and structured ecological thin (a mixture of thin from below and gap creation).     

Environmental Exposure of Aquatic and Terrestrial Biota to Triclosan and Triclocarban1

Abstract: The synthetic biocides triclosan (5‐chloro‐2‐(2,4‐dichlorophenoxy)phenol) and triclocarban (3,4,4′‐trichlorocarbanilide) are routinely added to a wide array of antimicrobial personal care products and consumer articles. Both compounds can persist in the environment and exhibit toxicity toward a number of biological receptors. Recent reports of toxicological effects in wildlife, human cell cultures, and laboratory animals have heightened the interest in the occurrence of these biocide and related toxic effects. The present study aimed to summarize published environmental concentrations of biocides and contrast them with toxicity threshold values of susceptible organisms. Environmental occurrences and toxicity threshold values span more than six orders of magnitude in concentration. The highest biocide levels, measured in the mid parts‐per‐million range, were determined to occur in aquatic sediments and in municipal biosolids destined for land application. Crustacea and algae were identified as the most sensitive species, susceptible to adverse effects from biocide exposures in the parts‐per‐trillion range. An overlap of environmental concentrations and toxicity threshold values was noted for these more sensitive organisms, suggesting potential adverse ecological effects in aquatic environments. Affirmative evidence for this is lacking, however, since studies examining environmental occurrences of biocides vis‐à‐vis the health and diversity of aquatic species have not yet been conducted.     

A Geochemical Record of Precession-Induced Cyclic Eastern Mediterranean Sedimentation: Implications for Northern Sahara Humidity During the Pliocene

The chemical composition of lithogenic components in Pliocene sediments from the eastern Mediterranean displays periodic variations that are related to earth's orbital parameters owing to changes in insolation of the northern hemisphere. This can be explained by two different paleoclimatic/palaeoceanographic scenarios. During oligotrophic periods, similar to those persisting in the modern Mediterranean, sedimentation is rather uniform, and sediments receive high proportions of eolian material from the surrounding deserts. During more humid intervals sedimentation is dominated by fluviatile material that has been introduced by the Nile and northern borderland rivers. Higher nutrient loads associated with enhanced riverine input and a change in water circulation led to eutrophication, water column anoxia, and sapropel deposition in the eastern Mediterranean. Our investigations confirm earlier works claiming that in large parts of the northern Sahara palaeoclimatic conditions changed frequently from arid to more humid. Our results suggest that these changes in the Pliocene match with the approximately 22-ka insolation cyclicity.

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Zusammenfassung   Der Chemismus lithogener Komponenten plioz?ner Sedimente des ?stlichen Mittelmeers weist periodische ?nderungen auf, die mit den Orbitalparametern der Erde und dadurch hervorgerufenen Variationen der Sonneneinstrahlung im Bereich der Nordhemisph?re einhergehen. Dadurch entstehen zwei gegens?tzliche pal?oklimatische bzw. pal?ozeanographische Szenarien. In Zeiten mit geringen Niederschl?gen und oligotrophen Bedingungen im Mittelmeer, wie sie auch heute vorherrschen, ist die Sedimentation sehr stark von ?olischen Staubeintr?gen angrenzender Wüstengebiete gekennzeichnet. Demgegenüber dominiert in feuchten Klimaperioden die Sedimentation von fluviatilem Material, das durch den Nil und Flüsse der n?rdlich an das Mittelmeer grenzenden Gebiete eingetragen wird. Die durch Zirkulations?nderungen sowie den N?hrstoffeintrag der Flüsse induzierten eutrophen Bedingungen führten schlie?lich zur Ausbildung von Wassers?ulen-Anoxia und der Ablagerung von Sapropelen im ?stlichen Mittelmeer. Unsere Untersuchungen unterstützen frühere Forschungsergebnisse, wonach in weiten Teilen der n?rdlichen Sahara ein h?ufigerer Wechsel zwischen ariden und humideren Klimabedingungen stattfand. Nach unseren Ergebnissen folgte dieser rhythmische Wechsel im Plioz?n dem Insolationszyklus von ca. 22 ka.

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Received: 16 September 1998 / Accepted in revised form: 28 December 1998