scholarly journals The geometry of habitat fragmentation: effects of distribution patterns on short-term species persistence

2018 ◽  
Author(s):  
Felix May ◽  
Benjamin Rosenbaum ◽  
Frank M. Schurr ◽  
Jonathan M. Chase
Keyword(s):  
Fragment Size ◽  
Land Use Changes ◽  
Species Distributions ◽  
Distribution Patterns ◽  
Habitat Amount ◽  
Species Persistence ◽  
Persistence Probability ◽  
Positive Effects ◽  
Per Se ◽  
Geometric Effects

AbstractLand-use changes cause habitat loss and fragmentation and are thus important drivers of anthropogenic biodiversity change. However, there is an ongoing debate about how fragmentationper seaffects biodiversity in a given amount of habitat. We illustrate why it is important to distinguish two different aspects of fragmentation to resolve this debate: (i) geometric fragmentation effects, which exclusively arise from the spatial distributions of species and habitat fragments, and (ii) demographic fragmentation effects due to reduced fragment size, increased isolation, or edge effects. While most empirical studies are primarily interested in quantifying demographic fragmentation effects, geometric effects are typically invoked only as post-hoc explanations of biodiversity responses to fragmentationper se. Here, we present an approach to quantify geometric fragmentation effects on species persistence probability. We illustrate this approach using spatial simulations where we systematically varied the initial abundances and distribution patterns (i.e. random, aggregated, and regular) of species as well as habitat amount and fragmentationper se.As expected, we found no geometric fragmentation effects when species were randomly distributed. However, when species were aggregated, we found positive effects of fragmentationper seon persistence probability for a large range of scenarios. For regular species distributions, we found weakly negative geometric effects. These findings are independent of the ecological mechanisms which generate non-random species distributions. Our study helps to reconcile seemingly contradictory results of previous fragmentation studies. Since intraspecific aggregation is a ubiquitous pattern in nature, our findings imply widespread positive geometric fragmentation effects. This expectation is supported by many studies that find positive effects of fragmentationper seon species occurrences and diversity after controlling for habitat amount. We outline how to disentangle geometric and demographic effects of fragmentation, which is critical for predicting the response of biodiversity to landscape change.

scholarly journals Influence of Landscape Structure on Toucans and Parrots in the Fragmented Landscape of Los Tuxtlas, Mexico

2021 ◽  
Vol 14 ◽  
pp. 194008292110499
Author(s):  
Marisela Martínez-Ruiz ◽  
Miguel A. De Labra-Hernández ◽  
Fernando César Gonçalves Bonfim ◽  
Eliana Cazetta
Keyword(s):  
Landscape Structure ◽  
Forest Cover ◽  
Bird Species ◽  
Edge Density ◽  
Primary Forest ◽  
Forest Loss ◽  
Fragmented Landscape ◽  
Los Tuxtlas ◽  
Habitat Amount ◽  
Positive Effects

Background and Research Aims: Habitat amount plays an important role in determining the presence and abundance of bird species in modified landscapes, whereas habitat fragmentation has shown little effects. Toucans (Ramphastidae) and parrots (Psittacidae) are large-bodied primary consumers and among the most representative birds in Neotropical forests. They are highly sensitive to habitat loss; nevertheless, their response to fragmentation has been poorly assessed leading to contradictory results. Here, we evaluate the influence of landscape structure on toucans and parrots in the tropical forest of Los Tuxtlas, Mexico. Methods: We censused birds in 12 landscapes of Los Tuxtlas and used a multi-scale landscape approach to assess the influence of landscape composition and configuration on the number of individuals of toucans and parrots. Results: We found that the most important and positive predictor of toucans and parrots was the amount of primary forest cover in the landscape. Forest fragmentation had positive effects on the number of toucan individuals, whereas parrots had negative responses to patch density but positive responses to edge density in the landscape. Conclusion: Our results suggest that primary forest loss is the main threat for toucans and parrots in Los Tuxtlas. Implications for conservation: Future conservation and land management must consider the protection of large and small remnants of primary forest and avoid additional forest loss in order to preserve toucan and parrots and their functional roles in human-modified Neotropical landscapes.

Alloxan Diabetes and Demonstrated Direct Action of Insulin on Metabolism of Isolated Perfused Rat Liver

1957 ◽  
Vol 192 (1) ◽  
pp. 33-42 ◽  
Author(s):  
David E. Haft ◽  
Leon L. Miller
Keyword(s):  
Alloxan Diabetes ◽  
Direct Action ◽  
Operative Procedure ◽  
Diabetic Rats ◽  
Isolated Perfused Rat Liver ◽  
Perfused Rat Liver ◽  
Insulin Administration ◽  
Positive Effects ◽  
Per Se ◽  
Partial Correction

The direct effect of insulin was studied in intact surviving livers removed from normal and alloxan-diabetic rats and perfused for 4 hours with rat blood containing acetate-1-C14. Changes due to diabetes per se were a) decreased lipogenesis from acetate, b) increased ureogenesis, and c) increased incorporation of acetate into carbohydrate. The positive effects of insulin consisted of an at least partial correction of the depressed lipogenesis characteristic of diabetes and of fasting, and a net removal of glucose from the perfusate after the 1st hour. The action of insulin was inhibited in most of the experiments with ketotic liver donors, and also in many experiments in which the operative procedure was accompanied by excessive trauma. Insulin administration depressed gluconeogenesis from acetate and lowered ketogenesis in experiments with alloxan diabetic donors.

The saltmarsh vegetation of the lower Uilkraals River

Bothalia ◽  
1994 ◽  
Vol 24 (2) ◽  
pp. 229-233
Author(s):  
M. O'Callaghan
Keyword(s):  
Great Influence ◽  
Species Distributions ◽  
Distribution Patterns ◽  
Western Cape

Approximately 40 ha of saltmarsh exist around the Uilkraals River. The distribution patterns of species in these marshes are described and compared with patterns found in other marshes in the Western Cape. The marshes might superficially resemble a mosaic of species, but each element of the mosaic could be compared with vegetation in other systems. Peculiar salinity and tidal features are postulated as having a great influence on species distributions at this river.

scholarly journals Immigration Rates in Fragmented Landscapes – Empirical Evidence for the Importance of Habitat Amount for Species Persistence

PLoS ONE ◽  
2011 ◽  
Vol 6 (11) ◽  
pp. e27963 ◽  
Author(s):  
Thomas Püttker ◽  
Adriana A. Bueno ◽  
Camila dos Santos de Barros ◽  
Simone Sommer ◽  
Renata Pardini
Keyword(s):  
Empirical Evidence ◽  
Habitat Amount ◽  
Species Persistence ◽  
Fragmented Landscapes

“Brain-Specific” Nutrients: A Memory Cure?

2002 ◽  
Vol 3 (1) ◽  
pp. 12-38 ◽  
Author(s):  
Mark A. McDaniel ◽  
Steven F. Maier ◽  
Gilles O. Einstein
Keyword(s):  
Alzheimer’S Disease ◽  
Older Adults ◽  
Alzheimer's Disease ◽  
Animal Studies ◽  
Memory Decline ◽  
Memory Tests ◽  
Positive Effects ◽  
Age Related ◽  
Per Se ◽  
The Brain

We review the experimental evaluations of several widely marketed nonprescription compounds claimed to be memory enhancers and treatments for age-related memory decline. We generally limit our review to double-blind placebo-controlled studies. The compounds examined are phos-phatidylserine (PS), phosphatidylcholine (PC), citicoline, piracetam, vinpocetine, acetyl-L-carnitine (ALC), and antiox-idants (particularly vitamin E). In animals, PS has been shown to attenuate many neuronal effects of aging, and to restore normal memory on a variety of tasks. Preliminary findings with humans, though, are limited. For older adults with probable Alzheimer's disease, a single study failed to demonstrate positive effects of PS on memory performance. For older adults with moderate cognitive impairment, PS has produced consistently modest increases in recall of word lists. Positive effects have not been as consistently reported for other memory tests. There is one report of consistent benefits across a number of memory tests for a subset of normal adults who performed more poorly than their peers at baseline. The choline compounds PC and citicoline are thought to promote synthesis and transmission of neurotransmitters important to memory. PC has not proven effective for improving memory in patients with probable Alzheimer's disease. The issue remains open for older adults without serious degenerative neural disease. Research on citicoline is practically nonexistent, but one study reported a robust improvement in story recall for a small sample of normally aging older adults who scored lower than their peers in baseline testing. Animal studies suggest that piracetam may improve neuronal efficiency, facilitate activity in neurotransmitter systems, and combat the age-related decrease in receptors on the neuronal membrane. However, for patients with probable Alzheimer's disease, as well as for adults with age-associated memory impairment, there is no clear-cut support for a mnemonic benefit of piracetam. Vinpocetine increases blood circulation and metabolism in the brain. Animal studies have shown that vinpocetine can reduce the loss of neurons due to decreased blood flow. In three studies of older adults with memory problems associated with poor brain circulation or dementia-related disease, vinpocetine produced significantly more improvement than a placebo in performance on global cognitive tests reflecting attention, concentration, and memory. Effects on episodic memory per se have been tested minimally, if at all. ALC participates in cellular energy production, a process especially important in neurons, and in removal of toxic accumulation of fatty acids. Animal studies show that ALC reverses the age-related decline in the number of neuron membrane receptors. Studies of patients with probable Alzheimer's disease have reported nominal advantages over a range of memory tests for ALC-treated patients relative to placebo groups. Significant differences have been reported rarely, however. Whether ALC would have mnemonic benefits for aging adults without brain disease is untested as far as we know. Antioxidants help neutralize tissue-damaging free radicals, which become more prevalent as organisms age. It is hypothesized that increasing antioxidant levels in the organism might retard or reverse the damaging effects of free radicals on neurons. Thus far, however, studies have found that vitamin E does not significantly slow down memory decline for Alzheimer's patients and does not produce significant memory benefits among early Parkinson's patients. Neither did a combination of vitamins E and C significantly improve college students' performance on several cognitive tasks. In sum, for most of the “brain-specific” nutrients we review, some mildly suggestive effects have been found in preliminary controlled studies using standard psychometric memory assessments or more general tests designed to reveal cognitive impairment. We suggest that future evaluations of the possible memory benefits of these supplements might fruitfully focus on memory processes rather than on memory tests per se.

Dietary nitrate supplementation reduces the O2cost of walking and running: a placebo-controlled study

2011 ◽  
Vol 110 (3) ◽  
pp. 591-600 ◽  
Author(s):  
Katherine E. Lansley ◽  
Paul G. Winyard ◽  
Jonathan Fulford ◽  
Anni Vanhatalo ◽  
Stephen J. Bailey ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Physiological Responses ◽  
Dietary Supplementation ◽  
Moderate Intensity ◽  
Controlled Study ◽  
Time To Exhaustion ◽  
Exercise Tests ◽  
Positive Effects ◽  
Severe Intensity ◽  
Per Se

Dietary supplementation with beetroot juice (BR) has been shown to reduce resting blood pressure and the O2cost of submaximal exercise and to increase tolerance to high-intensity cycling. We tested the hypothesis that the physiological effects of BR were consequent to its high NO3−content per se, and not the presence of other potentially bioactive compounds. We investigated changes in blood pressure, mitochondrial oxidative capacity (Qmax), and physiological responses to walking and moderate- and severe-intensity running following dietary supplementation with BR and NO3−-depleted BR [placebo (PL)]. After control (nonsupplemented) tests, nine healthy, physically active male subjects were assigned in a randomized, double-blind, crossover design to receive BR (0.5 l/day, containing ∼6.2 mmol of NO3−) and PL (0.5 l/day, containing ∼0.003 mmol of NO3−) for 6 days. Subjects completed treadmill exercise tests on days 4 and 5 and knee-extension exercise tests for estimation of Qmax(using31P-magnetic resonance spectroscopy) on day 6 of the supplementation periods. Relative to PL, BR elevated plasma NO2−concentration (183 ± 119 vs. 373 ± 211 nM, P < 0.05) and reduced systolic blood pressure (129 ± 9 vs. 124 ± 10 mmHg, P < 0.01). Qmaxwas not different between PL and BR (0.93 ± 0.05 and 1.05 ± 0.22 mM/s, respectively). The O2cost of walking (0.87 ± 0.12 and 0.70 ± 0.10 l/min in PL and BR, respectively, P < 0.01), moderate-intensity running (2.26 ± 0.27 and 2.10 ± 0.28 l/min in PL and BR, respectively, P < 0.01), and severe-intensity running (end-exercise O2uptake = 3.77 ± 0.57 and 3.50 ± 0.62 l/min in PL and BL, respectively, P < 0.01) was reduced by BR, and time to exhaustion during severe-intensity running was increased by 15% (7.6 ± 1.5 and 8.7 ± 1.8 min in PL and BR, respectively, P < 0.01). In contrast, relative to control, PL supplementation did not alter plasma NO2−concentration, blood pressure, or the physiological responses to exercise. These results indicate that the positive effects of 6 days of BR supplementation on the physiological responses to exercise can be ascribed to the high NO3−content per se.

scholarly journals Niche Characterization of Shrub Functional Groups along an Atlantic-Mediterranean Gradient

Forests ◽  
2021 ◽  
Vol 12 (8) ◽  
pp. 982
Author(s):  
Adriana E. Olthoff ◽  
Carolina Martínez-Ruiz ◽  
Josu G. Alday
Keyword(s):  
Functional Groups ◽  
Environmental Gradients ◽  
Land Use Changes ◽  
Distribution Patterns ◽  
National Forest Inventory ◽  
Future Climate Change ◽  
Natural Forests ◽  
Northern Spain ◽  
Response Curves ◽  
The North

The identification of the factors controlling the understory species distribution and abundance is essential to understand the ecology and dynamics of natural forests and their management response. We assess the relationships between environmental gradients and shrub functional groups distribution patterns and niche characteristics in a transitional area between the Eurosiberian and Mediterranean biogeographic regions in Northern Spain. Here, 772 plots from the 3rd Spanish National Forest Inventory were used. Shrub functional groups respond to the same complex environmental gradients as trees, i.e., the north-south climatic gradient and a slope gradient. Unimodal response curves of shrub functional groups and families dominate along both gradients, providing evidence of successful functional turnover. Similar to tree species, the niche location of functionally related shrubs is close. Functional groups occupying environments with sharp contrast or transitional environments have the broadest niches, whereas those specialized functional groups occupying localized habitats showed the narrowest niches. The knowledge of shrub species distributions and niche characteristics along complex environmental gradients will improve our ability to discuss potential conservation management goals or threats due to land-use changes and future climate change.

scholarly journals Protected areas in Central Mexico - are they fit in promoting species persistence under climate and land use changes?

2021 ◽  
Vol 260 ◽  
pp. 109186
Author(s):  
Fernando Chacón-Prieto ◽  
Clarita Rodríguez-Soto ◽  
Angela P. Cuervo Robayo ◽  
Julio César Carbajal Monroy ◽  
Diogo Alagador
Keyword(s):  
Land Use ◽  
Protected Areas ◽  
Land Use Changes ◽  
Central Mexico ◽  
Species Persistence

scholarly journals Population trends of passage and wintering barn swallows (Hirundo Rustica) in Peninsular Malaysia

2021 ◽  
Vol 880 (1) ◽  
pp. 012055
Author(s):  
N A Ismail ◽  
U N S Daud ◽  
S M Nor ◽  
M S Mansor
Keyword(s):  
Species Distribution Model ◽  
Land Use Changes ◽  
Geographical Area ◽  
Distribution Patterns ◽  
Peninsular Malaysia ◽  
Hirundo Rustica ◽  
Distribution Model ◽  
Barn Swallow ◽  
Barn Swallows ◽  
Using Data

Abstract In Peninsular Malaysia, passage and wintering Barn Swallows (Hirundo rustica) often congregate at nocturnal roosts in towns. As a Holarctic migratory species, it is at risk of population collapse. Despite extensive research, little is known about this species in its wintering grounds, especially in the tropics. This study aimed to determine how climate change influences the population growth of this species across a geographical area over a decade, from 2009 to 2019. A species distribution model was constructed using data obtained from the eBird database – a citizen science project – of records from diverse locations. We used the Kernel Density tool in ArcGIS to describe Barn Swallow density and expansion pattern across Peninsular Malaysia. We demonstrate that the Barn Swallow’s population has fallen by about 27.1% over the last decade. In 2009, the species was dispersed in two distinct areas: Perlis to Pulau Pinang; and the Pahang region bordering Selangor and Negeri Sembilan; in addition, some individuals chose to winter in south-eastern Johor. Within ten years, the flock has descended from Perlis to the northwest corner of Perak, while the vast wintering area in Pahang has decreased and stretched down to Melaka and Johor. The differences in Barn Swallow numbers and distribution patterns observed in this study could be a result of climate and land use changes which have caused this species to spread to parts of other wintering regions, altering the arrival and departure times of migration, thereby interfering with its breeding season.

Klima der Angst oder Respekt auf Augenhöhe? Erfahrungen von Hartz IV-Beziehenden mit Jobcentern im Zuge der Corona-Pandemie

2021 ◽  
Vol 70 (10-11) ◽  
pp. 651-669
Author(s):  
Fabian Beckmann ◽  
Rolf G. Heinze ◽  
Dominik Schad ◽  
Jürgen Schupp
Keyword(s):  
Social Policy ◽  
Policy Implications ◽  
Unconditional Security ◽  
Job Seekers ◽  
Positive Effects ◽  
Street Level ◽  
Hartz Iv ◽  
Positive Experiences ◽  
Per Se

Zusammenfassung Im Zuge der Corona-Pandemie wurden der Zugang zu Leistungen der Grundsicherung vereinfacht und die Zugangsvoraussetzungen zur Gewährung von Sozialleistungen sowie die Disziplinierung der Leistungsbeziehenden abgeschwächt. Bislang ist unklar, welche Erfahrungen Leistungsbeziehende mit diesem vereinfachten Zugang gemacht haben. Der Beitrag untersucht dies auf Basis einer quantitativen Erhebung unter Grundsicherungsbeziehenden des Kreises Recklinghausen. Im Fokus stehen die Beurteilung der Interaktion mit den Jobcenter-Beschäftigten seitens der Leistungsbeziehenden, die Zufriedenheit mit dem Hartz IV-System und die Einstellungen zum vereinfachten Zugang zur Grundsicherung im Jahr 2020. Die Befunde zeigen: Leistungsbeziehende nehmen das Jobcenter mehrheitlich nicht als Ort der Angst und Disziplinierung wahr, obgleich Scham ebenso Teil der Realität ist. Positive Erfahrungen mit dem Jobcenter gehen einher mit positiven Effekten auf die Beurteilung des Hartz IV-Systems, was die Bedeutung der Jobcenter als street-level bureaucracy unterstreicht. Eine Verstetigung wesentlicher Elemente des vereinfachten Zugangs wird mehrheitlich befürwortet, allerdings mit der Ausnahme einer dauerhaften Aussetzung von Sanktionen. Der Beitrag diskutiert abschließend sozialpolitische Implikationen für eine neujustierte Grundsicherung. Abstract: Climate of Fear or Respect at Eye Level? Experiences of Hartz IV-Recipients with Jobcentres during the COVID-19 pandemic In the wake of the COVID-19 pandemic, the access to basic security benefits for job seekers was facilitated by promoting unconditional security elements and weakening disciplinary measures for recipients. So far, it is unclear what experiences benefit recipients have had with these new regulations. The article investigates this question on the basis of a quantitative survey of basic security benefit recipients. We focus on the evaluation of the interaction with job centre-employees, the satisfaction with the Hartz IV-system and attitudes towards the pandemic-related regulations. The findings show: benefit recipients do not per se perceive job centres as places of fear and harassment, although feelings of shame are also part of their reality. Positive experiences with job centres show positive effects on the evaluation of the Hartz IV-system, which underlines the important role of job centres as street-level bureaucracies. Making the new regulations permanent is supported by the vast majority, although a permanent renunciation of sanctions is not favoured. Finally, the article discusses social policy implications for a redesigned basic security system.

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