Low Disturbance Areas Research Articles

Diversidad vegetal a lo largo de un gradiente de perturbación en un ecosistema semi-árido en el Centro de México

Antecedentes y Objetivos: La fragmentación del hábitat y otras alteraciones humanas pueden causar la pérdida de fertilidad del suelo, erosión y la pérdida de biodiversidad, entre otras; sin embargo, la información en zonas áridas es limitada. El objetivo de este trabajo fue determinar los efectos de un gradiente de disturbio en la composición de especies en dos tipos de vegetación en un ecosistema semi-árido del centro de México.Métodos: Se seleccionaron seis zonas de estudio diferentes en la zona de Cerro Colorado, tres de matorral xerófilo y tres de bosque tropical caducifolio. Se determinó la diversidad genérica y específica utilizando 10 cuadrantes (un total de 60), localizados al azar, durante los meses de mayo-junio de 2011. Se generó un índice de perturbación basado en las actividades que se registraron en la región como pastoreo y tala, entre otros. Las áreas de alto, medio y bajo disturbio se identificaron en el matorral xerófilo y bosque tropical caducifolio.Resultados clave: Los resultados mostraron que el bosque tropical caducifolio es más diverso que el matorral xerófilo, además de que es posible utilizar a los arbustos Cnidoscolus tehuacanensis y Mimosa luisana como indicadores, ya que se encontraban en lugares con altos niveles de perturbación. Por otro lado, en el bosque tropical caducifolio, tres géneros (Thevetia, Acacia y Bursera) presentan altas abundancias relativas en lugares conservados, mientras que en el matorral xerófilo solo uno (Parkinsonia) tiene este patrón.Conclusiones: De los resultados se puede inferir que en hábitats semiáridos del Centro de México las actividades antropogénicas juegan un papel importante en la diversidad florística, ya que facilitan el establecimiento de algunas plantas nativas que pueden ser consideradas como colonizadoras. Estas pueden ser utilizadas como indicadoras de los disturbios con la finalidad de determinar la viabilidad de hábitat para otros taxa.

Pine Harvest Impact on Soil Structure of a Dystric Cambisol (Humic)

Traffic of heavy machinery at harvest and log extraction causes structural degradation of the soil, but studies on the effects of forest harvesting on soils with high organic matter content and exchangeable Al are scarce. The objective of this study was to evaluate the effect of mechanized forest harvesting operations on a Dystric Cambisol (Humic) with high organic matter (more 50 g kg1) content and exchangeable Al (more 6,0 cmolc kg-1), reforested with Pinus taeda L. The evaluated harvesting system were the whole-tree, in which the feller-buncher cuts and lays the trees down in bundles; the skidder drags the tree bundles up near a road; and the harvester delimbs and cuts the trees into short logs, stacking them on the roadside to be loaded onto trucks. The areas were evaluated for soil conditions at pre-harvest, prior to harvest, and at post-harvest, consisting of areas of low disturbance, high disturbance, forest residues and log yards. The effects of compaction after forest harvesting are observed by the decrease in total porosity (especially biopores and macropores), soil saturated hydraulic conductivity, and stability of aggregates. After forest harvesting, soil compaction was observed in all evaluated situations, but with different depths depending on operation type and the intensity of traffic carried in each area.

On the use of predator traits and distribution in environmental impact assessment: the trophic/dispersal sufficiency concept

Environmental change can alter both species distribution range patterns at a regional scale and their feeding habits at a local scale. While several studies have highlighted the mechanisms driving such changes separately, little is known on their combined effect on the local communities. In this manuscript, we used both feeding and distributional traits of macro-benthic species and examined their combined response across an environmental gradient induced by an aquaculture unit. Our results mainly suggest that specialized predators with narrow geographic distributions and niches were more sensitive to environmental change than the less specialized groups. Moreover, under harsh environmental conditions, predatory species with a wide dispersion capacity can sustain viable populations through niche generalization. In contrast, in areas of low environmental disturbance, predatory species with a more restricted dispersal capability (i.e. some endemic species) can coexist via niche differentiation. In this context, our findings contribute towards a better understanding of benthic communities’ functional response to environmental change and may be of use in environmental impact assessment.

Do squirrels in human disturbed areas become habituated to humans? A measure of flight initiation distance across disturbance gradients

Human population growth results in destruction of natural habitats, although some animals are adapting to living in areas with human disturbance. North American red squirrels (Tamiasciurus hudsonicus) may be one such species that is successfully adapting to living alongside humans. Flight initiation distance, the distance at which an animal flees from an approaching predator, may act as an indicator of habituation to humans. I predicted that if North American red squirrels were habituating to humans, their flight initiation distance would decrease along a gradient of increasing human disturbance. To examine this, I measured flight initiation distances of 39 North American red squirrels across eight sites, classified as low, medium or high human disturbance areas. No significant difference was found in mean flight initiation distances between disturbance levels, indicating that squirrel flight initiation distance may not be sensitive to small scales of human disturbance gradients.

Influences of Human and Livestock Density on Winter Habitat Selection of Mongolian Gazelle (Procapra gutturosa)

Human and livestock related disturbances of habitat selection by ungulates are topics of global concern, as they have profound impacts on ungulate survival, population density, fitness, and management; however, differences in ungulate habitat use under different human and livestock densities are not fully understood. Mongolian gazelle (Procapra gutturosa), an endemic ungulate species on the Asia-European steppe, faces varying intensities of human and livestock disturbances in the area around Dalai Lake, China. To investigate how habitat selection strategies vary as disturbance intensity changes, we randomly set 20 transects containing 1486 plots, on which we conducted repeated surveys of 21 ecological factors during the winters in the period of 2005-2008. We aimed to: 1) determine the critical factors underlying habitat selection of the gazelles; 2) determine the gazelles' habitat preferences in this area; 3) determine how habitat selection varies with disturbance intensity and explore the primary underlying mechanism. We used binary-logistic regressions and information theoretic approaches to build best-fit habitat selection models, and calculated resource selection functions. Sixty-six herds, 522 individuals, and 499 tracks were recorded. Our results indicate that snow depth and aboveground biomass are the main factors affecting habitat selection by Mongolian gazelle throughout the district in winter. Thin snow cover and abundant aboveground biomass are preferred. Avoiding disturbance was the primary factor accounting for habitat selection in low disturbance areas, although with increasing human or live-stock-related disturbance, gazelle maintained a reduced distance to the source of the disturbance. Presumably owing to that shift, movement costs were more important as disturbance increased. In addition, Mongolian gazelle selected habitats based on topographical features promoting greater visibility where disturbance was lower. We suggest several management implications of our findings for this ungulate species will contribute to the effective conservation of Mongolian gazelle in the Dalai Lake area.

Effects of developmental conditions on nestling American Kestrel ( Falco sparverius) corticosterone concentrations

How nestling birds respond to stressful situations may constitute an important survival component that has lasting developmental effects on the hypothalamic pituitary adrenal (HPA) axis. As birds are exposed to increasing amounts of potential anthropogenic stressors through land use change, understanding how these factors contribute to HPA development is important. We examined whether conditions experienced during the nestling stage affected free-living American Kestrel ( Falco sparverius) HPA activity prior to fledging. Kestrels experienced varying levels of human disturbance around their nest and we classified this environmental exposure as high or low environmental human disturbance based on traffic patterns and land use. We then exposed some broods from high and low disturbance areas to a standardized disturbance protocol. Prior to fledging we collected blood samples from 25-day-old nestlings immediately after capture and 15 min post-capture. Corticosterone (CORT) did not vary with environmental human disturbance levels, disturbance protocol treatment, or with an interaction between environmental human disturbance and disturbance protocol treatment suggesting that nestling kestrels may not perceive external conditions related to human disturbance as stressful or kestrels may acclimate to disturbance. We also compared the relative effects of environmental human disturbance outside the nest cavity, conditions within the nest cavity (brood size), and individual condition (nestling fat scores) on baseline and stress-induced CORT. Baseline CORT did not vary with human disturbance level, brood size or fat score. Fat scores best explained stress-induced CORT with nestlings in better condition displaying elevated CORT. These results suggest that individual variation is more likely to explain HPA development compared to nest conditions or the external environment. This study demonstrates the importance of considering the effects of developmental conditions on the stress response at several scales.

Reproductive potential and seed fate of Sclerocarya birrea subsp. caffra (marula) in the low altitude savannas of South Africa

Even though Sclerocarya birrea subsp. caffra (marula) is a well-studied, keystone tree species with high ecological, commercial and cultural value, significant gaps in our understanding of its reproductive biology exist, particularly the factors limiting fruit and seed production, seed fate and the persistence of the seed bank. Therefore, a detailed quantitative assessment of these factors was conducted at five sites in the low altitude savannas of South Africa. Sites varied with respect to fire regime, large mammals, geology and rainfall. Most sites showed male-biased secondary sex ratios and the minimum fruiting stem diameter ranged between 7.1 and 15.7 cm across sites. Sites with higher levels of disturbance (fire and large browsers) had trees producing fruit at larger minimum stem diameters than sites with lower levels of disturbance. Fruit production was highly variable between individuals, within and between sites, and from year to year. Variability in fruit production across years at one site was greater than the variability across sites in one year, indicating that drivers such as weather, insect herbivory, fire and predator numbers, which vary annually, play a greater role than more constant drivers such as mammalian herbivory, soil types or long-term rainfall. No significant relationship was found between environmental variables (rainfall and temperature) and annual fruit production, indicating a trade-off between vegetative growth and reproduction between years. Since marula fruits are large and heavy, the species relies primarily on mammalian dispersal agents such as the African elephant, which have also been shown to increase the germination rate. However, rodents also appear to play a significant role in seed dispersal. Seed predation rates tend to be highest in areas of low disturbance (no fire and no large browsers). While marula has a small persistent seed bank, recruitment appears to be reliant on the current season's fruit crop. This study provides a detailed quantitative assessment of important reproductive and seed fate vital rates for future population modelling.

Influences of Design and Landscape Placement Parameters on Amphibian Abundance in Constructed Wetlands

As natural wetlands disappear, constructed wetlands may play vital roles in amphibian conservation. However, previous investigations have concluded that artificial wetlands do not adequately replace lost wildlife habitat. Nevertheless, constructed wetlands serve as breeding habitat for amphibians where extensive natural wetland loss has occurred. To investigate the roles of engineered wetland features on amphibian abundance, we surveyed 49 constructed wetlands throughout northern Missouri. Cricket frogs (Acris crepitans), bullfrogs (Lithobates catesbeianus), and leopard frogs (Lithobates blairi/sphenocephalus complex) each occurred in over 80% of surveyed wetlands. Salamanders and hylid frogs were rarely encountered. We used an information theoretic approach to examine relationships between individual species and habitat features associated with wetland designs and placements. We found that models incorporating design features of open water ponds best explained abundances of most commonly encountered species. At the placement level, models that included nearby aquatic habitat ranked highest for common species. Salamanders and most hylid frogs responded positively to aquatic vegetative cover but negatively to fish abundance and anthropogenic disturbance-related features in the landscape. Our results indicate that to be effective amphibian conservation tools, constructed wetlands should be fish-free, heavily vegetated, include shallows, and placed within areas of low anthropogenic disturbance.

A preliminary assessment of the impact of disturbance and handling on Weddell seals of McMurdo Sound, Antarctica

There has been growing concern over the impact of increased human disturbance and research effects on Antarctic species. The Weddell seal of McMurdo Sound in particular has been used as a model species for over four decades of research, with some individuals handled multiple times over a single season. Using opportunistic data, we performed an assessment of blood indicators in adult males (n = 26) and adult females (n = 24) based on high versus low disturbance areas, with results showing no variation in overall seal health. In addition, we performed a preliminary analysis of blood and faecal indicators of inflammation and stress collected from adult, non-lactating females (n = 13) handled twice in less than two weeks for research purposes. There was no indication of a change in white blood cells, platelets, globulins or haptoglobins, or faecal corticosteroids (all P > 0.05). While based on a small, opportunistic sample size with limited power in some cases, preliminary results indicate there is no acute impact of repeated handling or difference in overall traffic level on adult Weddell seals.

Census of the mountain gorilla Gorilla beringei beringei population in Bwindi Impenetrable National Park, Uganda

Mountain gorillas Gorilla beringei beringei are Critically Endangered, with just two small populations: in Bwindi Impenetrable National Park in south-western Uganda and the nearby Virunga Volcanoes on the borders with Rwanda and Uganda. A survey of the Bwindi population was carried out in 2002 and results were compared with the previous census in 1997. Our estimate of total population size increased over that period by c. 7% to 320 individuals and the structure and distribution of the population were largely unchanged. Signs of human disturbance were more common in 2002 than 1997, and gorillas tended to be found in areas of relative low disturbance. This suggested that disturbance could be a constraint on population growth and distribution but demographic stochasticity may also be responsible for the observed level of population change over a short time period. Other potential limiting factors, including habitat availability and disease, are discussed. While conservation activities in Bwindi have probably contributed to the stability of the population, strengthening of law enforcement and continued vigilance are needed to ensure the population's long-term growth and survival.

3D CAD reconstructions of lens suture planes within specific zones of discontinuity from primate lenses

How nestling birds respond to stressful situations may constitute an important survival component that has lasting developmental effects on the hypothalamic pituitary adrenal (HPA) axis. As birds are exposed to increasing amounts of potential anthropogenic stressors through land use change, understanding how these factors contribute to HPA development is important. We examined whether conditions experienced during the nestling stage affected free-living American Kestrel (Falco sparverius) HPA activity prior to fledging. Kestrels experienced varying levels of human disturbance around their nest and we classified this environmental exposure as high or low environmental human disturbance based on traffic patterns and land use. We then exposed some broods from high and low disturbance areas to a standardized disturbance protocol. Prior to fledging we collected blood samples from 25-day-old nestlings immediately after capture and 15 min post-capture. Corticosterone (CORT) did not vary with environmental human disturbance levels, disturbance protocol treatment, or with an interaction between environmental human disturbance and disturbance protocol treatment suggesting that nestling kestrels may not perceive external conditions related to human disturbance as stressful or kestrels may acclimate to disturbance. We also compared the relative effects of environmental human disturbance outside the nest cavity, conditions within the nest cavity (brood size), and individual condition (nestling fat scores) on baseline and stress-induced CORT. Baseline CORT did not vary with human disturbance level, brood size or fat score. Fat scores best explained stress-induced CORT with nestlings in better condition displaying elevated CORT. These results suggest that individual variation is more likely to explain HPA development compared to nest conditions or the external environment. This study demonstrates the importance of considering the effects of developmental conditions on the stress response at several scales.

Current forms and extent of retention areas within a selectively logged blackbutt forest in NSW: a case study

Summary This case study estimates the cost (in terms of reduced royalty) of the current commitment to protecting non-wood values by retaining ecologically sensitive areas in a selectively logged blackbutt forest (Eucalyptus pilularis Sm.) Blackbutt is the most important native timber-producing species in N.S.W. Within these forests, which frequently have a history of relatively low impact logging (group selection), reserved or low-disturbance areas have been set in place to safeguard ecologically “sensitive areas”. These retained areas are expected to complement and interact with the selectively logged forest to improve the maintenance of non-wood values and provide a reference for the long-term impacts of logging. The current forms and extent of reserves and low disturbance areas are examined in the Coffs Harbour Management Area on the north coast of N.S.W. To broadly estimate some of the cost attributable to the commitment to non-wood values, the current royalty value of the harvestable timber set aside...

Abundances and physiological properties of deep-water seaweeds from Carolina outer continental shelf

The morphology, physiology, and relative abundances of two deep-water seaweed assemblages off Cape Fear, North Carolina, were examined, one at 30 m and the other at 42 m depth. Both sites are subtropical areas of low physical disturbance. In situ O 2-exchange rates for abundant species were measured. Species showed net photosynthesis at ≤ 40 μE · m −2 · s −1 (≈ 0.01 I 0). Thin flat species, such as Dictyopteris hoytii Tayl., Dictyota cervicornis Kütz., and D. Divaricata Lamour., had higher photosynthetic capacity (> 2 × ) and greater pigment content than species with other thallus forms (calcified, coarsely branched, leathery); however, thin flat species are not biomass-abundant year-round at the high-diversity 30-m site. Rather, perennial species with coarsely branched or thick leathery thalli predominated. The annual species, Dictyota divaricata, dominated (> 85% cover) at the low-diversity 42-m site. Low tissue-N levels and relatively high CN̈ atom ratios suggested nutrient limitation. Macroalgae with calcified, coarsely branched, and leathery thalli, particularly Zonaria tournefortii (Lamour.) Mont., Galaxaura obtusata (Ellis et Soland.) Lamour., and Eucheuma isiforme (C. Ag.) J. Ag. had CN̈ ratios of ≈ 25, well above the Redfield ratio of 6.6 for balanced growth. A measured intrusion of cooler nutrient-rich bottom water, presumably of continental-slope origin, resulted in an almost three-fold increase in ambient N, which was usually < 0.4 μM NO 3 − + NO 2 − during summer. This source and N flux out of surrounding sediments are undoubtedly a critical source of nutrients, particularly during the summer, the period of highest growth. This study suggests that opposing selective pressures have influenced abundances in these deep-water low-disturbance habitats. Species with thin flat thalli have high photosynthetic performance and, possibly, increased N-uptake ability, but show restricted seasonality; perhaps seaweeds with lower productivity maintain year-round abundances due to a large investment of photosynthate into supportive tissue, and concomitant abilities of perennation and vegetative spread.