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<p> High-latitude ecosystems store large amounts of carbon in soil organic matter and are among the most vulnerable to climate change. In particular, fire severity and frequency are increasing in boreal ecosystems, and these events are likely to have direct and indirect effects on climate feedbacks via increased emission of carbon (C) from soil and changes in vegetation composition, respectively. In this study we created experimental burns of three severities in the northeastern Siberian arctic, near Cherskiy, RU, and quantified dissolved C, nitrogen (N), and phosphorus (P), and microbial respiration and extracellular enzyme activities at 1-day, 8-days, and 1-year post-fire. </p><p> Our objective was to determine how fire affects C, N, and P pools, soil microbial processes, and how these effects scale across severity and time since fire. We found labile C and nutrients increased immediately post-fire, but appeared similar to unburned controls within a week. Phosphorus alone remained elevated through 1-year post-fire. Leucine aminopeptidase activities initially increased with fire severity, but by 1-year, activities decreased with fire severity at a rate an order of magnitude faster. Fire severity suppressed phosphatase and ?-glucosidase activities at all time points. Soil respiration was reduced by half in high severity plots 1-year post-fire, while net rates of N mineralization increased by an order of magnitude. We found that changes in soil C and nutrient pools, soil respiration, and net N mineralization rates responded in a threshold-fashion to fire severity, although P was uncoupled from C and N by changing at a distinct severity threshold. Extracellular enzyme activities and edaphic variables scaled linearly with fire severity. The interaction of threshold and linear response curves to fire severity may help explain the variability across studies in soil microbial community responses to fire. Microbial communities recovering from more severe fires have the possibility to decrease future ecosystem C losses through reduced respiration. The changing fire regime in permafrost ecosystems has the potential to alter soil microbial community dynamics, the retention of nutrients, and the stoichiometry of C, N, and P availability.</p>

<p> Biodiversity has decreased due to anthropogenic activities, and extinction rates are currently one hundred to one thousand times greater than the background rate. While the connection between deforestation and biodiversity loss is well documented within tropical rainforest ecosystems, comparatively little is known about the effects of desertification on biodiversity in dryland ecosystems. Drylands, which cover nearly half the terrestrial surface and are highly vulnerable to desertification, are among the most endangered ecosystems. To understand how biodiversity responds to environmental degradation in these fragile ecosystems, I studied arthropod diversity within a human-modified landscape suffering from deforestation and desertification in the Sahel of western Senegal. My specific objective was to determine whether arthropod, beetle, spider and ant diversity differed between protected areas of tropical dry forest and surrounding communal lands suffering from desertification. I established 12 quadrats spaced homogenously throughout each protected area as well as adjacent communal land at three different locations (Beersheba, Bandia and Ngazobil). Within each quadrat, I measured canopy closure, characterized vegetation and collected arthropods using pitfall traps during the 2014 dry (May) and rainy (September) seasons.</p><p> I collected 123,705 arthropods representing 733 morphospecies, 10,849 beetles representing 216 morphospecies, 4,969 spiders representing 91 morphospecies and 59,183 ants representing 45 morphospecies. Results showed protected areas contained greater arthropod and spider diversity than communal lands, beetle diversity varied depending on location and season, and communal lands contained greater ant diversity than protected areas (<i>P</i> &le; 0.05). My results illustrate the importance of a multi-taxa approach in understanding biodiversity response to anthropogenic disturbances. Conserving arthropod diversity in the Sahel will require the creation and preservation of more protected areas of a variety of sizes and successional stages as well as the adoption and extension of land-restorative techniques such as Zai and farmer managed natural regeneration (FMNR).</p>

Lactation provides the singular source of nourishment to the offspring of mammals. This nutrition source also contains a diverse microbiota affecting the development and health of the newborn. Here, we examined the milk microbiota in water deer (Hydropotes inermis, the most primitive member of the family Cervidae), reindeer (Rangifer tarandus, the oldest semi-domesticated cervid), and the dairy goat (Capra aegagrus, member of the family Bovidae), to determine if common milk microbiota species were present across all three ruminant species. The results showed that water deer had the highest bacterial diversity, followed by reindeer, and then goat. Unifrac distance and correspondence analyses revealed that water deer harbored an increased abundance of Pseudomonas spp. and Acinetobacter spp., while milk from reindeer and goat was dominated by unclassified bacteria from the family Hyphomicrobiaceae and Bacillus spp., respectively. These data indicate significant differences in the composition of milk-based bacterial communities. The presence of Halomonas spp. in three distinct co-occurrence networks of bacterial interactions revealed both common and unique features in milk niches. These results suggest that the milk of water deer and reindeer harbor unique bacterial communities compared with the goat, which might reflect host microbial adaptation caused by evolution.

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Patterns in the use of gastropod shells by hermit crabs were examined for a complex of hermit crabs inhabiting the Alligator Harbor region of Florida. To assess field use patterns, two sampling techniques, a straight-line transect method and a predation site method, were used. The transect method yielded large animals in relatively undamaged shells of a few gastropod genera, and the results were influenced by habitat. The predation site method yielded a wide size range of individuals in damaged shells of many gastropod species. / Simulated gastropod predation sites attract a variety of hermit crabs. Experiments with simulated predation sites revealed that chemical cues are necessary for location of newly liberated shells. Attraction to a simulated predation site is species specific for hermit crabs and is directly related to the genus of gastropod flesh at the site. In addition, there is a significant positive correlation between amount of flesh at a site and size of crab attracted. These results are discussed in terms of spatial and temporal patterns of hermit crab shell acquisition. / Regardless of the collection method, however, shell use patterns have been evaluated by using empirically derived measures of shell adequacy. Shell adequacy or shell fit has been inferred by using two indices; the shell adequacy index and the utilization efficiency index. Both indices contain statistical biases which render the interpretation of the indices ambiguous. I conclude by describing field and laboratory experiments which demonstrate that determination of shell adequacy is a complex problem which cannot be assessed by simple methods. / Source: Dissertation Abstracts International, Volume: 43-06, Section: B, page: 1721. / Thesis (Ph.D.)--The Florida State University, 1982.

Results of a two year study of colonization of two introduced trees, Quercus acutissima and Castanea crenata, by leaf-mining insects are described in Chapter I. More species of miners completed larval development on Q. acutissima, which has more local native congeners than does C. crenata. However, all miners found on Q. acutissima (subgenus Lepidobalanus) are found on native red oaks (subgenus Erythrobalanus). Leaf-miner density and survivorship were higher on C. crenata than on Q. acutissima, although most of these differences are attributable to two species. Parasitism rates for these species and all miners analyzed together were lower on C. crenata than on Q. acutissima. For some species, reduced parasitism on C. crenata was partially offset by increased predation. Successful colonization of C. crenata by at least one dominant miner may be related to the higher nitrogen content of this host. / In Chapter II, I tested the hypothesis that a significant amount of larval leaf-miner mortality on water oak, Quercus nigra, results from nutritional inadequacy of the host tree. I altered phytochemistry of water oaks with urea- and ammonium-nitrate-fertilization and drought stress. Survivorship of all leaf miners together, and of several dominant species analyzed separately, increased on fertilized trees. Generally, miners responded more to urea-fertilization of trees than to ammonium-nitrate-fertilization. Higher survivorship on fertilized trees was associated with reduced predation. Enhanced larval leaf-miner survivorship correlated with increased densities in 1981, but not in 1980. Leaf-miner survivorship and density increased on drought-stressed trees in both years. / Larvae of two bivoltine species of leaf miners feed only on young, second-flush leaves of their host trees in north Florida. In Chapter III, I show that first-generation larval densities of these species on 30 water oaks is positively correlated with amount of secondary leaf production in 1980 and 1981. During this study, five trees abscised their leaves and reflushed new ones at atypical times of the growing season. Densities of the phenologically specialized miners increased dramatically on these trees only when refoliation coincided with emergence of ovipositing adults. / Source: Dissertation Abstracts International, Volume: 43-06, Section: B, page: 1719. / Thesis (Ph.D.)--The Florida State University, 1982.