It has typically been assumed that habitat destruction, characterized by habitat loss and fragmentation, has consistently negative effects on biodiversity. While numerous empirical studies have shown ...the detrimental effects of habitat loss, debate continues as to whether habitat fragmentation has universally negative effects. To explore the effects of habitat fragmentation, we developed a simple model for site‐occupancy dynamics in fragmented landscapes. With the model, we demonstrate that a competition–colonization trade‐off can result in nonlinear oscillatory responses in biodiversity to both habitat loss and fragmentation. However, the overall pattern of habitat loss reducing species richness is still established, in line with empirical observations. Interestingly, the existence of localized oscillations in biodiversity can explain the mixed responses of species richness to habitat fragmentation per se observed in nature, thereby reconciling the debate on the fragmentation–diversity relationship. Therefore, this study offers a parsimonious mechanistic explanation for empirically observed biodiversity patterns in response to habitat destruction.
Abstract
Recent extreme wildfire seasons in several regions have been associated with exceptionally hot, dry conditions, made more probable by climate change. Much research has focused on extreme ...fire weather and its drivers, but natural wildfire regimes—and their interactions with human activities—are far from being comprehensively understood. There is a lack of clarity about the ‘causes’ of wildfire, and about how ecosystems could be managed for the co-existence of wildfire and people. We present evidence supporting an ecosystem-centred framework for improved understanding and modelling of wildfire. Wildfire has a long geological history and is a pervasive natural process in contemporary plant communities. In some biomes, wildfire would be more frequent without human settlement; in others they would be unchanged or less frequent. A world without fire would have greater forest cover, especially in present-day savannas. Many species would be missing, because fire regimes have co-evolved with plant traits that resist, adapt to or promote wildfire. Certain plant traits are favoured by different fire frequencies, and may be missing in ecosystems that are normally fire-free. For example, post-fire resprouting is more common among woody plants in high-frequency fire regimes than where fire is infrequent. The impact of habitat fragmentation on wildfire crucially depends on whether the ecosystem is fire-adapted. In normally fire-free ecosystems, fragmentation facilitates wildfire starts and is detrimental to biodiversity. In fire-adapted ecosystems, fragmentation inhibits fires from spreading and fire suppression is detrimental to biodiversity. This interpretation explains observed, counterintuitive patterns of spatial correlation between wildfire and potential ignition sources. Lightning correlates positively with burnt area only in open ecosystems with frequent fire. Human population correlates positively with burnt area only in densely forested regions. Models for vegetation-fire interactions must be informed by insights from fire ecology to make credible future projections in a changing climate.
Tens of thousands of species are threatened with extinction as a result of human activities. Here we explore how the extinction risks of terrestrial mammals and birds might change in the next 50 ...years. Future population growth and economic development are forecasted to impose unprecedented levels of extinction risk on many more species worldwide, especially the large mammals of tropical Africa, Asia and South America. Yet these threats are not inevitable. Proactive international efforts to increase crop yields, minimize land clearing and habitat fragmentation, and protect natural lands could increase food security in developing nations and preserve much of Earth's remaining biodiversity.
1. Conservation biology faces the challenge of ensuring species persistence in increasingly modified landscapes. Agriculture covers a large proportion of the Earth's surface, but the degree to which ...crop production is compatible with species use of the landscape is still uncertain, particularly for woodland carnivores with large territories. Here, we focus on the Iberian lynx Lynx pardinus, an emblematic endangered species that has coexisted for centuries with human-modified Mediterranean mosaics, as a case study to unravel habitat and dispersal preferences in heterogeneous landscapes. 2. We estimated species resource selection from ≈40 000 telemetry locations for 48 GPS-collared individuals covering all the current Iberian lynx range, including more fragmented areas where the species was reintroduced from 2009. We differentiated GPS locations within home ranges (to estimate habitat suitability) and those corresponding to dispersal or exploratory movements (to estimate landscape permeability). We built mixed conditional logistic regression models with 12 land cover classes, terrain slope and roads as predictors. 3. We found that lynx response to agriculture largely depends on the crop type and on the presence of natural vegetation remnants. Lynx largely avoided intensive cultivation areas such as irrigated arable lands when establishing home ranges, but frequently selected permanent crops (olive groves) and/or heterogeneous agricultural lands, which were used with smaller differences to the most preferred shrubland or forest covers than reported in previous studies. 4. Such differences further narrowed down when lynx moved outside home ranges, with some agricultural covers being as permeable as shrublands for lynx dispersal. The species dispersal plasticity was also evidenced by a much weaker avoidance of roads and steep terrain when dispersing than when selecting territories. 5. Synthesis and applications. We conclude that (i) the widespread consideration of all agricultural lands within a single (and usually regarded as unsuitable) class for the study and management of woodland or forest species is not supported and that (ii) the ability of woodland species to use fragmented and heterogeneous agricultural landscapes may have been underestimated, which may mislead conservation measures due to a priori assumptions that do not relate to the actual species responses to heterogeneous land covers. We suggest that Iberian lynx conservation and reintroduction may be successful in a wider set of more heterogeneous areas than previously thought, including mainly well-conserved Mediterranean woodlands but also some extensive agricultural lands with permanent crops and natural vegetation remnants.
Cross-sectional studies suggest that sleep fragmentation is associated with cognitive performance in older adults. We tested the hypothesis that sleep fragmentation is associated with incident ...Alzheimer's disease (AD) and the rate of cognitive decline in older adults.
Prospective cohort study.
Community-based.
737 community dwelling older adults without dementia.
Sleep fragmentation was quantified from up to 10 consecutive days of actigraphy. Subjects underwent annual evaluation for AD with 19 neuropsychological tests. Over a follow-up period of up to 6 years (mean 3.3 years), 97 individuals developed AD. In a Cox proportional hazards model controlling for age, sex, and education, a higher level of sleep fragmentation was associated with an increased risk of AD (HR = 1.22, 95%CI 1.03-1.44, P = 0.02 per 1SD increase in sleep fragmentation). An individual with high sleep fragmentation (90
percentile) had a 1.5-fold risk of developing AD as compared with someone with low sleep fragmentation (10
percentile). The association of sleep fragmentation with incident AD did not vary along demographic lines and was unchanged after controlling for potential confounders including total daily rest time, chronic medical conditions, and the use of common medications which can affect sleep. In a linear mixed effect analysis, a 0.01 unit increase in sleep fragmentation was associated with a 22% increase in the annual rate of cognitive decline relative to the average rate of decline in the cohort (Estimate = -0.016, SE = 0.007, P = 0.03).
Sleep fragmentation in older adults is associated with incident AD and the rate of cognitive decline.
Lim ASP; Kowgier M; Yu L; Buchman AS; Bennett DA. Sleep fragmentation and the risk of incident alzheimer's disease and cognitive decline in older persons.
2013;36(7):1027-1032.
•Discrete element model (DEM) study of agglomerate fragmentation due to impact.•Effects of agglomerate size, adhesion strength and impact velocity have been considered.•Results are fitted using ...dimensional parameters.•Discrete fragmentation model (DFM) build based upon dimensionless parameter study.•DFM applicable to wide range of challenges in process engineering.
Discrete element simulations of agglomerates impacting other agglomerates and agglomerates impacting a wall have been carried out. The agglomerates consist of multiple, small primary particles. In the simulations, we have varied the adhesiveness of the primary particles, the agglomerate size, as well as the impact velocity of the impact. The quantitative trends in the results from the simulations have been captured by a dimensional analysis of the problem, and the resulting fit of a resolved, micro-scale modelling of the impacts has been used to construct a macro-scale discrete fragmentation model to describe agglomerate fragmentation using the framework of the discrete element model, but without the necessity of elucidating the behaviour of each individual primary particle. The working of the discrete fragmentation model has been validated with the results from the detailed micro-scale simulations.
Negative landscape‐scale fragmentation effects are often inferred from negative patch‐scale edge effects. I tested this cross‐scale extrapolation using two evaluations. First, I searched for studies ...that estimated the direction of both a patch‐scale edge effect and a landscape‐scale fragmentation effect. The directions were concordant and discordant in 55% and 45% of cases, respectively. Second, I extracted from the literature a sample of landscape‐scale fragmentation effects on individual species. Then, for each species I searched for studies from which I could calculate the slope of its patch‐scale edge effect. Species showing negative patch‐scale edge effects were nearly equally likely to show negative or positive landscape‐scale fragmentation effects, and likewise for species showing positive patch‐scale edge effects. The results mean that the efficacy of policies related to habitat fragmentation cannot be inferred from observed patch‐scale edge effects. Such policies require landscape‐scale evidence, comparing species' responses in landscapes with different levels of fragmentation.
Farmland fragmentation is an important factor of farmland abandonment in China, including landscape fragmentation in biophysical conditions and tenure fragmentation in property conditions. Both ...farmland fragmentation has different effects and different management strategies. However, it is still unclear whether the farmland tenure fragmentation (FTF) aggravates farmland abandonment and its extent when the farmland landscape fragmentation (FLF) remains unchanged. Therefore, we combined the large-scale sample survey (5479 samples) and geographical analysis to distinguish FTF and FLF, and use logistic regression and Tobit regression model to analyze the impact of FTF on farmland abandonment. In addition, we take farmland transfer as a moderation variable to explore whether the farmland transfer significantly alleviates the abandonment of farmland. Here we show that the farmland abandonment rate decreased by 16.8% when the average plot area increased by 1 mu (1 mu = 666.67 m2) in China, and in the place where the extent of FLF is lower, the impact of FTF on farmland abandonment is greater. And farmland transfer plays a significant regulatory role between the FTF and the abandoned rate of farmland. This study helps to distinguish our understanding of the impact of FTF and FLF on farmland abandonment and provides a scientific basis for decision-makers to reduce the abandonment of farmland, ensure national food security, and promote rural revitalization.
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•The farmland fragmentation of tenure and landscape was distinguished.•The farmland abandonment rate decreased by 16.8% when the average plot area increased by 1 mu.•The lower the FLF, the more significant the impact of FTF on farmland abandonment.•The regulatory effect of land transfer in the impact mechanism of FTF on farmland abandonment was further explored.
For an infectious disease such as the coronavirus disease 2019 (COVID-19) to spread, contact needs to be established between an infected host and a susceptible one. In a range of populations and ...infectious diseases, peer-to-peer contact modes involve complex interactions of a pathogen with a fluid phase, such as isolated complex fluid droplets or a multiphase cloud of droplets. This is true for exhalations including coughs or sneezes in humans and animals, bursting bubbles leading to micron-sized droplets in a range of indoor and outdoor settings, or impacting raindrops and airborne pathogens in foliar diseases transferring pathogens from water to air via splashes. Our mechanistic understanding of how pathogens actually transfer from one host or reservoir to the next remains woefully limited, with the global consequences that we are all experiencing with the ongoing COVID-19 pandemic. This review discusses the emergent area of the fluid dynamics of disease transmission. It highlights a new frontier and the rich multiscale fluid physics, from interfacial to multiphase and complex flows, that govern contact between an infected source and a susceptible target in a range of diseases.
Although habitat fragmentation is often assumed to be a primary driver of extinction, global patterns of fragmentation and its relationship to extinction risk have not been consistently quantified ...for any major animal taxon. We developed high-resolution habitat fragmentation models and used phylogenetic comparative methods to quantify the effects of habitat fragmentation on the world’s terrestrial mammals, including 4,018 species across 26 taxonomic Orders. Results demonstrate that species with more fragmentation are at greater risk of extinction, even after accounting for the effects of key macroecological predictors, such as body size and geographic range size. Species with higher fragmentation had smaller ranges and a lower proportion of high-suitability habitat within their range, andmost high-suitability habitat occurred outside of protected areas, further elevating extinction risk. Our models provide a quantitative evaluation of extinction risk assessments for species, allow for identification of emerging threats in species not classified as threatened, and provide maps of global hotspots of fragmentation for the world’s terrestrial mammals. Quantification of habitat fragmentation will help guide threat assessment and strategic priorities for global mammal conservation.
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