The effects of food quality and food quantity on crustacean zooplankton’s feeding rate have been analyzed in the present study. In two experiments, we studied the clearance rates (CRs) of Daphnia pulex on different algal diets (Scenedesmus obliquus, nontoxic Microcystis sp. PCC7806 and Anabeana flos-aquae) varying in carbon to phosphorus (C:P) ratios and quantities (concentrations). In order to investigate the effects of different algal diets on the feeding of cladocerans, the mixture of S. obliquus, Microcystis sp. PCC7806 and A. flos-aquae was also fed to D. pulex during a 72-h period. Our results showed: (1) D. pulex had different clearance rates from the three mono-specific P-rich algal diets, while no significant difference among clearance rates was observed among the three mono-specific P-poor algal diets; (2) D. pulex increased its clearance rates when it fed on mono-specific P-poor S. obliquus and A. flos-aquae, while a P-poor mixture of M. aeruginosa and A. flos-aquae reduced the clearance rate; (3) A U-shaped quadratic function provided a good fit to the clearance rate and C:P ratios because the clearance rate of D. pulex in both low and high C:P categories were significantly higher than in the moderate C:P category (C:P value = 219). Our results demonstrated that filaments and C:P ratios of algae strongly influence the feeding of crustacean zooplankton. ‘Compensatory feeding’ occurred in the mono-specific, P-poor algal diets but not in the mixed diets. Moreover, the clearance rate of zooplankton was the lowest in the moderate P stoichiometric category. Our experiments suggest that the morphology and C:P ratios of algal diets have important effects on the feeding of Daphnia, and the P stoichiometric characteristics in mixed diets may play an important role in the feeding of large-sized cladocerans.

We studied the influence and correlation of soil improvement, farmland ecological protection, soil fertilization, and field infrastructure construction on the quality grade of well-fertilized farmland in the engineering measures of well-fertilized farmland construction. Taking Xiao County of the Anhui Province as the study area, based on the software platforms of SPSS, ArcGIS10.6, and the county farmland resource management information system, we investigated the farmland quality changes of well-facilitated farmland before and after construction using the fuzzy evaluation method and analytic hierarchy process. We used principal component analysis and the gray relational method to analyze the impact and correlation of various engineering measures on farmland quality. The farmland quality grade in the study area was improved by a 0.59 grade after the construction of the well-facilitated farmland. Well-facilitated farmland construction engineering measures mainly affected the farmland quality through 12 factors, such as the soil bulk density, tillage layer texture, irrigation and drainage guarantee rates, forest network density, and field road accessibility. There is a strong correlation between these factors and the characteristics of farmland quality; the degrees of correlation were 0.865–0.610, respectively. The highest correlation degree was 0.939 between the deep plowing and deep loosening soil improvement project and the improvement of the well-facilitated basic farmland quality; this was followed by soil fertilization with an increased application of organic fertilizer, farmland ecological protection, and the field infrastructure project with correlations of 0.936, 0.857, and 0.563, respectively. Represented by the improvement of farmland fertility, the soil improvement project had the strongest impact on well-facilitated farmland quality. The soil fertility project, farmland ecological protection project, and the field infrastructure project were the second most important, with very close degrees of correlation.

The Amur tiger (Panthera tigris altaica) is a flagship and umbrella species of forest ecosystems in northeastern Asia. Climate change is profoundly and irreversibly affecting wildlife habitat suitability, especially for large mammals. To effectively protect the Amur tiger, it is necessary to understand the impact of climate change on the quality and the connectivity of its habitat. We used the species distribution models combined with the latest Shared Socioeconomic Pathway (SSP) climate scenarios to predict current and future changes in habitats and corridors. We found the following: (1) The total area of the Amur tiger’s suitable habitat currently amounts to approximately 4941.94 km², accounting for 27.64% of the study area represented by two adjacent national parks. Among these habitats, the highly suitable areas are mainly located on the both sides of the Sino-Russian border. The landscape connectivity remains relatively stable, and the degree of fragmentation in highly suitable habitats is low. (2) Although the suitable habitat of the Amur tiger shows an expansion trend under most climate scenarios (excluding SSP3-7.0), the area of suitable habitat within the entire study region does not increase significantly. Therefore, we should implement conservation measures to facilitate the continued expansion of suitable habitat for the Amur tiger. The quantity and length of landscape connectivity corridors are expected to vary in response to changes in core habitat patches, while the centroid of highly suitable habitats is also expected to shift to different extents. In such circumstances, new ecological corridors need to be constructed, while existing natural ecological corridors should be preserved.