Predicting bryophyte diversity in grassland and eucalypt-dominated remnants in subhumid Tasmania

Aim To determine the environmental factors associated with bryophyte diversity in remnants in a fragmented, agricultural landscape. Location Eighty‐two remnants of tussock grassland, eucalypt woodland and eucalypt forest in the subhumid Midlands region of Tasmania, Australia. Methods Remnants were surveyed for bryophytes and predictor variables, such as vascular plant cover, climate, and topography. Management histories for each remnant were compiled using both site observation and landowner surveys. Bryophyte cover, richness, and composition were related to the independent variables using simple correlation and general linear models. Results We found weak relationships between the dependent variables and the fragmentation variables (remnant area, remnant perimeter to area ratio, distance to nearest remnant, distance to nearest larger remnant, and remnant age). Instead, climatic variables were important in predicting bryophytes, in particular those affecting humidity (minimum temperature of the coldest month, precipitation). Despite extensive sheep grazing in this landscape, grazing was not correlated with bryophyte diversity. Bryophyte diversity was not explained by vascular plant richness and was only weakly explained by composition, but was predicted by the cover of vascular plants. There was greater bryophyte cover and richness and different composition where the cover of native vascular plants was lower. Main conclusions The implications of our results are that all remnants, regardless of area, age and isolation, appear to be valuable for bryophyte conservation in this highly altered landscape. Our results also suggest that the cover of the vascular plant community, rather than its diversity, holds promise as a guide to bryophyte diversity. Bryophyte composition was similar between sites and a focus on the most species‐rich sites may be the best conservation strategy in this ecosystem.     

Sediment type and the clonal size greatly affect the asexual reproduction,productivity, and nutrient absorption of Vallisneria natans

Most aquatic vegetation restorations involve the transplantation of submerged macrophytes. Sediment type and the clonal size are of great significance as they determine the fate of submerged macrophytes. In order to ensure successful restoration, a simulation experiment was conducted using aquarium mesocosms to investigate the response of stolon propagation capacity, the morphological features and productivity of Vallisneria natans for four types of sediment (lake mud [L], lake mud + sand [L + S, 50:50, v/v mixture], sand [S], clay [C]), and three types of clonal sizes. Results showed that sediment types significantly affected V. natans biomass accumulation, stolon propagation ability, ramet morphological characteristics, and productivity, where the asexual reproduction ability and productivity ranked as L > L + S > S > C in four sediment types. Total biomass, maximum net production, number of ramets, root diameter, number of stolons, and stolon propagation rate were all highest in L. In L and L + S, the plant chlorophyll content was higher than in S and C. The root diameter and the ratio of aboveground/underground biomass in S were the smallest among the four sediments. Moreover, when more V. natans seedlings were linked, more ramets and biomass were produced. The stolon propagation rate was ranked as the stolon with single seedling greater than the stolon with two‐linked seedlings greater than the stolon with three‐linked seedlings in L and L + S. The concentration of total nitrogen, total phosphorus, and NO₃^?‐N in water was remarkably reduced in four aquariums. Findings provide a scientific basis for restoring submerged macrophytes in different sediment settings.     

Habitat selection,interspecific interactions and landscape composition

Summary I argue here that, from the perspective of any individual, most landscapes are composed of only three basic types of habitats. These are: (1) source habitat in which reproduction exceeds mortality and the expected per capita growth rate is greater than one; (2) sink habitat, in which limited, reproduction is possible but will not on average, compensate for mortality and the per capita rate of growth is between zero and one; and (3) unusable habitat, which comprises the matrix of all habitats that are never exploited by the species in question, and in which patches of source and sink habitats are embedded. Unlike earlier source-sink models, this model explicitly considers the effects that substituting one type of habitat for another has on the equilibrium size of a population and the interactions between species which can use both source and sink habitats. The model demonstrates that the equilibrium size of a species' population can sometimes be increased by substituting unusable habitat for sink habitat. Thus, even though the average patch quality in the landscape may be decreased, the overall quality of the landscape can increase. For two species with distinct habitat preferences, interactions between species can vary qualitatively as well as quantitatively as a function of the relative abundances of each of the habitat types. The model also shows that the interactions between species are particularly sensitive to the relative costs of moving between patches and sampling patches to determine their quality. Recent fragmentation of natural landscapes may increase the cost of searching for usable (source or sink) patches. Under some conditions, the interspecific interactions may be substantially more negative (competitive) than the interactions that evolved in the original natural landscape, further reducing population sizes and increasing the likelihood of competitive exclusion in fragmented modern landscapes.     

千岛湖陆桥岛屿地表蚂蚁群落物种多样性空间格局及其影响因素

为了探讨千岛湖岛屿景观参数对地表蚂蚁群落物种α和β多样性空间格局的影响, 作者分别于2017和2018年的5-8月, 采用陷阱法、凋落物分拣法和手捡法调查了千岛湖33个岛屿上的地表蚂蚁群落, 并依据食性将其划分为捕食性蚂蚁和杂食性蚂蚁。利用回归模型分析了全部蚂蚁、捕食性蚂蚁和杂食性蚂蚁群落α和β多样性与岛屿景观参数的关系。结果表明, 岛屿面积对全部蚂蚁、捕食性蚂蚁和杂食性蚂蚁的物种丰富度均有显著的正向影响, 而隔离度则无显著作用。蚂蚁群落的β多样性由空间周转组分主导。岛屿面积差对全部蚂蚁、捕食性蚂蚁和杂食性蚂蚁群落β多样性的嵌套组分有正向影响, 隔离度差只对杂食性蚂蚁的总体β多样性有正向影响。因此, 岛屿面积是影响千岛湖地表蚂蚁群落物种丰富度的主要因素, 并且岛屿面积通过嵌套组分来影响蚂蚁群落的β多样性, 表现出选择性灭绝过程。此外, 不同食性蚂蚁可能因为扩散能力的差异对岛屿景观参数产生不同的响应。     

Effect of forest fragment size on tree diversity and population structure of humid subtropical forest of Meghalaya,India

The present study was conducted in subtropical humid forests of Meghalaya to study the distributional pattern of species, floristic composition, community structure and tree population structure.Forest fragments of varying sizes(0.5 ha, 1 ha, 2 ha and 5 ha) were used in the study.All of the forest fragments are distributed within the same altitudinal range, and had similar rainfall and temperature regimes.Four forest fragments were sampled using random quadrats to analyze the impact of fragment size on tree...     

Floral resources,body size,and surrounding landscape influence bee community assemblages in oak‐savannah fragments

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