Step-wise drops in modularity and the fragmentation of exploited marine metapopulations

Context

Many nearshore species are distributed in habitat patches connected only through larval dispersal. Genetic research has shown some spatial structure of such metapopulations and modeling studies have shed light onto possible patterns of connectivity and barriers. However, little is known about human impact on their spatial structure and patterns of connectivity.

Objectives

We examine the effects of fishing on the spatial and temporal dynamics of metapopulations of sedentary marine species (red sea urchin and red abalone) interconnected by larval dispersal.

Methods

We constructed a metapopulation model to simulate abalone and sea urchin metapopulations experiencing increasing levels of fishing mortality. We performed the modularity analysis on the yearly larval connectivity matrices produced by these simulations, and analyzed the changes of modularity and the formation of modules over time as indicators of spatial structure.

Results

The analysis revealed a strong modular spatial structure for abalone and a weak spatial signature for sea urchin. In abalone, under exploitation, modularity takes step-wise drops on the path to extinction, and modules breakdown into smaller fragments followed by module and later metapopulation collapse. In contrast, sea urchin showed high modularity variation, indicating high- and low-mixing years, but an abrupt collapse of the metapopulation under strong exploitation.

Conclusions

The results identify a disruption in larval connectivity and a pattern of collapse in highly modular nearshore metapopulations. These results highlight the ability of modularity to detect spatial structure in marine metapopulations, which varies among species, and to show early changes in the spatial structure of exploited metapopulations.

     

Occupancy pattern of a long-horned beetle in a variegated forest landscape: linkages between tree quality and forest cover across spatial scales

Context

Interactions between landscape-scale processes and fine-grained habitat heterogeneity are usually invoked to explain species occupancy in fragmented landscapes. In variegated landscapes, however, organisms face continuous variation in micro-habitat features, which makes necessary to consider ecologically meaningful estimates of habitat quality at different spatial scales.

Objectives

We evaluated the spatial scales at which forest cover and tree quality make the greatest contribution to the occupancy of the long-horned beetle Microplophorus magellanicus (Coleoptera: Cerambycidae) in a variegated forest landscape.

Methods

We used averaged data of tree quality (as derived from remote sensing estimates of the decay stage of single trees) and spatially independent pheromone-baited traps to model the occurrence probability as a function of multiple cross-scale combinations between forest cover and tree quality (with scales ranging between 50 and 400 m).

Results

Model support and performance increased monotonically with the increasing scale at which tree quality was measured. Forest cover was not significant, and did not exhibit scale-specific effects on the occurrence probability of M. magellanicus. The interactive effect between tree quality and forest cover was stronger than the independent (additive) effects of tree quality and particularly forest cover. Significant interactions included tree quality measured at spatial scales ≥200 m, but cross-scale interactions occurred only in four of the seven best-supported models.

Conclusions

M. magellanicus respond to the high-quality trees available in the landscape rather than to the amount of forest per se. Conservation of viable metapopulations of M. magellanicus should consider the quality of trees at spatial scales >200 m.

     

Physiological Response of Multiple Contrasting Rice (Oryza sativa L.) Cultivars to Suboptimal Temperatures

The physiological response of multiple rice cultivars, eighteen initially and eight cultivars later on, to suboptimal temperatures (ST) conditions was investigated in laboratory and outdoor experimental conditions. Treatment with ST decreased growth in different extents according to the cultivar and affected the PSII performance, determined by chlorophyll fluorescence fast‐transient test, and stomatal conductance, regardless the experimental condition. Two groups of cultivars could be distinguished on the base of their growth and physiological parameters. The group of cultivars presenting higher growths displayed optimal JIP values, and higher instantaneous water use efficiency (WUE_i), due to a lower Gs under ST, unlike cultivars showing lower growth values, which presented worse JIP values and could not adjust their Gs and hence their WUE_i. In this work, we detected at least two cultivars with superior tolerance to ST than the cold tolerant referent Koshihikari. These cultivars could be used as parents or tolerance donors in breeding for new crop varieties. On other hand, positive and significant correlations between data obtained from laboratory and outdoor experiments suggest that laboratory measurements of most of the above mentioned parameters would be useful to predict the response of rice cultivars to ST outdoor.     

Digestive Enzyme Activity during Larval Development of Black Snook,Centropomus nigrescens

Black snook, Centropomus nigrescens, have been identified as a promising candidate for aquaculture although, like many of the Centropomid species, high mortality associated with early larval stages presents a significant bottleneck to their commercialization. The digestive capacity of black snook larvae throughout the first 37 d after hatch (d.a.h.) was evaluated by quantifying digestive enzyme activities using biochemical techniques. Results showed that black snook larvae have alkaline proteases at hatching, which are known to be important during the first days of feeding for digestion. Toward the end of the study, acid proteases concentration increased (37 d.a.h.). Enzymes for lipid digestion, pancreatic lipase and bile salt‐activated lipase, were already present in the larvae before exogenous feeding commenced, and their activity increased with age and growth (length). Intracellular digestion, measured as the activity of leucine‐alanine peptidase, was high early on (5 d.a.h.) and decreased as development progressed (next 32 d). In contrast, alkaline phosphatase activity was lowest at first feeding and subsequently increased with age. Overall patterns in enzyme activity suggest the possibility of live feed weaning before 32 d.a.h. if artificial diets can be properly balanced.     

Flow alteration and thermal pollution depress modelled growth rates of an iconic riverine fish,the Murray cod Maccullochella peelii

The serial discontinuity concept (SDC) proposes that hypolimnetic‐releasing impoundments cause major disruptions to the naturally occurring physical, chemical and biological gradients of rivers but that this impact diminishes with distance downstream. Such a gradient in discharge, flow velocity and temperature regime occurs below a large hypolimnetic‐releasing impoundment, the Hume Dam, on the River Murray in south‐eastern Australia. To examine the effects of this disturbance gradient on a warm‐water large‐bodied freshwater fish, the Murray cod (Maccullochella peelii), a bioenergetics model was developed and calibrated to explore energy expended under differing water velocities and temperature regimes. Model simulations predicted negative growth of juveniles directly downstream of the impoundment, due largely to the energetic costs associated with active and, to a lesser extent, standard metabolism outweighing the achievable energetic gains through food consumption. As flow velocity and temperature regimes became more favourable downstream, so did the simulated growth of the species. It was not until +239 km downstream of the impoundment that the model predicted that flow velocity and temperature regimes were suitable for greater weight gains. The modelled growth responses of juvenile Murray cod are consistent with the predictions of the SDC, emphasising that changes in the bioenergetics of individuals are likely to be reflected in reduced growth rates under the changed flow velocity and temperature regimes imposed by disturbance gradients. This research represents a valuable step in the biological understanding of Murray cod within variable riverine environments and emphasises the urgency required to mitigate impacts associated with hypolimnetic impoundments.     

Comparative Characterization of Enzymatic Digestion from Fish and Soybean Meal from Simulated Digestive Process of Pacific Bluefin Tuna,Thunnus orientalis

The digestive process of the Pacific bluefin tuna (PBT), Thunnus orientalis, was simulated through two phases of in vitro digestion: acidic digestion with porcine pepsin, followed by alkaline digestion with pancreatic crude extract (PCE) obtained from the PBT to hydrolyze fish meal (FM) and soybean meal (SBM) as protein substrates. The crude protein from FM resulted in a lower degree of hydrolysis (73.3%) compared with SBM (79.2%). However, the resulting digested products showed that FM contained 35% more small peptides, with sizes <6.5 kDa than those from the starting material (>150 kDa). The SBM had an increase of only 1.3% in the similar peptide cut‐offs found after hydrolysis. These results suggested that FM appeared to be a better source of protein according to the amount of low‐molecular weight peptides. In addition, the proteolytic activity of PCE showed that 88.9% of its alkaline proteolytic activity corresponded to trypsin and 2.9% corresponded to chymotrypsin activity. The results shown here demonstrate that peptide sizes are important in identifying suitable protein sources for aquafeed production to reinforce the primary results obtained from the in vitro digestibility using the pH‐Stat system. These results also contribute to a better understanding of the digestibility process in aquatic organisms.     

Improved Cold and Drought Tolerance of Doubled Haploid Maize Plants Selected for Resistance to Prooxidant tert‐Butyl Hydroperoxide

To improve the abiotic stress tolerance of maize (Zea mays L.), doubled haploid (DH) plants were produced by in vitro selection of microspores exposed to tert‐butyl hydroperoxide (t‐BuOOH) as a powerful prooxidant This study investigated the tolerance of the progenies of t‐BuOOH‐selected DH lines to oxidative stress, cold and drought in controlled environment pot experiments by analyses of photosynthetic electron transport and CO₂ assimilation processes, chlorophyll bleaching and lipid peroxidation of leaves. Our results demonstrated that the t‐BuOOH‐selected DH plants exhibited enhanced tolerance not only to oxidative stress‐induced by t‐BuOOH but also to cold and drought stresses. In addition, they showed elevated activities of antioxidant enzymes such as superoxide dismutase, ascorbate peroxidase, catalase, glutathione reductase and glutathione S‐transferase when compared with the DH lines derived from microspores that were not exposed to t‐BuOOH and to the original hybrid plants. The results suggest that the simultaneous up‐regulation of several antioxidant enzymes may contribute to the oxidative and cold stress tolerance of the t‐BuOOH‐selected DH lines, and that the in vitro microspore selection represents a potential way to improve abiotic stress tolerance in maize.     

Maize defence mechanisms against the European corn borer,Ostrinia nubilalis Hübner (Lepidoptera: Crambidae)

Maize is arguably the most widely grown crop in the world, but it is often associated with one of its major insect pests, the European corn borer (ECB). The damage caused by this species to maize production is generally variable, but in many cases it is economically significant. This review paper provides an overview of the research findings on the natural plant defence mechanisms against ECB larvae published till now. What is resistance and how it is achieved, what is the chemical response of maize plants to insect feeding and how tolerance can be increased. A short introduction in breeding for resistance and a discussion if the mentioned traits can be used in conventional breeding in order to create maize hybrids less affected by ECB are given.     

Associations of fish with various types of littoral habitats in reservoirs

Fish associations with different types of littoral habitats were studied in four canyon‐shaped reservoirs in the Czech Republic in years 2010 and 2011 by gillnets. Two to three habitats per reservoir–beaches (former meadows), stump fields (former forest) and rubble slopes–were defined and sampled along the longitudinal axis of reservoirs. Effects of reservoir, habitat and locality (position along longitudinal axis) on fish biomass, abundance and species structure were tested for juvenile and adult fish separately. Hierarchical analysis of variance revealed that habitats differed significantly in fish biomass and abundance. Redundancy analysis showed that analysed environmental variables had significant influence on fish community structure. Most variability in community structure was explained by reservoir and then by combination of habitat and slope steepness. Locality position had the smallest influence on community structure. For both adult and juvenile fish total abundance and biomass, the most inhabited habitat was beaches; rubble slopes were the least inhabited. Habitat associations differed among species. Among adults, bream Abramis brama, white bream Blicca bjoerkna and roach Rutilus rutilus were associated with beaches and stump fields, whereas perch Perca fluviatilis, ruffe Gymnocephalus cernuus, asp Aspius aspius and pike Esox lucius were associated with rubble slopes. Bream, white bream, bleak Alburnus alburnus, roach, ruffe and pikeperch Sander lucioperca were associated with beaches among juveniles, whereas the only juvenile associated with rubble slopes was perch. We showed that most common species are associated with distinct habitats and also that utilisation of various littoral habitats differs in general.     

Successive grafting confers juvenility traits to adult Spanish red cedar (Cedrela odorata Linnaeus): a tool for the rescue of selected materials

New Forests - Spanish red cedar, Cedrela odorata L. (Meliaceae), is a valuable timber tree in tropical American forests. Existing demand for elite individuals endangers the conservation of...