Habitat overlap of juvenile and adult lake trout of Great Bear Lake: Evidence for lack of a predation gradient?     

Louise Chavarie  Kimberly L. Howland  Les N. Harris  Mike J. Hansen  Colin P. Gallagher  William J. Harford  William M. Tonn  Andrew M. Muir  Charles C. Krueger 《Ecology of Freshwater Fish》2019,28(3):485-498

A range of organisms, from plankton to fish, commonly shift their habitat distributions horizontally or vertically due to predation risk. Juvenile lake trout, Salvelinus namaycush, are generally viewed as occupying deep areas of lakes to decrease predation pressure from adults. In contrast, we found that juvenile lake trout from Great Bear Lake, NT, Canada, occupied a variety of habitats and from shallow to deep depths (0–150 m), overlapping with adult lake trout. No evidence occurred for a length depth‐based segregation (e.g., ontogenetic shift). Genetic variation was also similar among juveniles in the different depth zones. However, isotopic niches and C:N ratios among juveniles showed some variability in niche widths and positions for individuals caught from the 51–150 m zone compared to juvenile individuals caught from 0–20 m and 21–50 m zones. The uniformly distributed adult lake trout in Great Bear Lake may evenly distribute predation pressure (including cannibalism) across shallow‐ and deep‐water habitats more than in other lakes. As a result, juveniles may respond to differences in foraging opportunities rather than predation risks. Juvenile lake trout did not appear to conform to the general pattern of juveniles seeking a deep‐water refuge to reduce predation risks. In contrast, juvenile lake trout of Great Bear Lake displayed broad resource use across all depths and habitats.  相似文献   

一种捕食性螽蟖—黑背小绿螽的研究     

邓国荣  金孟肖 《中国生物防治》1985,(4)

黑背小绿螽的成虫、若虫均咬食三化螟卵块;并捕食白螟、斜纹夜蛾的卵;叶蝉、稻虱、稻蝗的低龄若虫。在南宁、贵县等地一年发生两代,以卵越冬,卵散产于茭白、姜苗、禾本科杂草等的叶鞘内侧及稻兜株间。用人工配制的代饲料饲养,所得的成虫能继代繁殖。在稻田及时补充散放一定数量的适龄虫体,对控制三化螟害虫有一定的作用。  相似文献   

Evaluating Domestic Sheep Survival with Different Breeds of Livestock Guardian Dogs     

Daniel Kinka  Julie K. Young 《Strength and Conditioning Journal》2019,72(6):923-932

Livestock guard dogs (LGDs; Canis familiaris) have been widely adopted by domestic sheep (Ovis aries) producers because they reduce predation by wild carnivores. LGDs were originally used in the United States to reduce coyote (Canis latrans) depredations, but their efficacy against a suite of large carnivores, including wolves (Canis lupus), brown bears (Ursus arctos), black bears (Ursus americanus), and cougars (Puma concolor), and whether specific breeds perform better than others remains unclear. To assess breed-specific effectiveness at reducing depredations from a suite of livestock predators, we compared survival rates of sheep protected by different breeds of LGDs, including three breeds from Europe (Turkish kangal, Bulgarian karakachan, and Portuguese cão de gado transmontano) and mixed-breed LGDs, “whitedog,” common in the United States. With the help of participating sheep producers, we collected cause-specific mortality data from domestic sheep in Idaho, Montana, Oregon, and Wyoming between 2013 and 2016. All three of the novel breeds of LGD tested were associated with overall reductions in sheep depredation relative to whitedogs, ranging from 61% to 95% (P < 0.05). In terms of predator-specific effectiveness, the Turkish kangal was associated with decreases in depredation from cougars (e^β = 0.31, 95% CI = 0.10–0.94, P = 0.04), black bears (e^β = 0.33, 95% CI = 0.28–0.37, P < 0.01), and coyotes (e^β = 0.56, 95% CI = 0.35–0.90, P = 0.02). The Bulgarian karakachan was associated with a decrease in coyote depredations (e^β = 0.07, 95% CI = 0.01–0.49, P < 0.01). The Portuguese transmontano was not associated with significant reductions in depredation hazard for any specific predator. Although variations in breed-specific effectiveness were subtle and nuanced, these findings will help livestock producers and wildlife managers make tailored decisions about how best to incorporate different breeds of LGD into sheep grazing regimes.  相似文献   

东方钝绥螨生物学及食量研究     

张守友 《昆虫天敌》1990,12(1):21-24

东方钝绥螨在昌黎地区每年大约发生23代左右。平均卵期1.8天,幼虫期0.7天、第一若虫期1.0天、第二若虫期1.5天、产卵前期4.6天、产卵期15.2天、雌成螨期20.5天、雄成螨期15.6天、生命周期为25.5天。平均日产卵量1.5粒,总卵量16粒。雌成螨日捕食山楂叶螨卵3粒及若螨0.46头,总捕食量为卵91粒,若螨43头及成山楂叶螨14头,对苹果全爪螨捕食量3.4头(雌成螨)。  相似文献   

Impaired littoral energy pathways cause a shift to pelagic resources by fish in recovering lake food webs     

Andreas Luek  George E. Morgan  Bjoern Wissel  John M. Gunn  Charles W. Ramcharan 《Ecology of Freshwater Fish》2013,22(3):348-360

Fish communities may increase in biomass and productivity due to energy subsidies from the littoral invertebrate community. In lakes recovering from acidification and metal contamination, such as those in Sudbury, Ontario, Canada, impaired benthic invertebrate communities (i.e., low diversity with higher abundance of small‐bodied taxa) allowed a critical test of the role of these littoral pathways on fish diet. We compared fish abundance, diversity, diet and biomass in eight recovering and eight reference lakes and related availability of the main littoral and pelagic invertebrate groups to fish diet regime using stable isotope analysis. A Bayesian mixing model (MixSIR) was used to estimate diet likelihood, and convex hull analysis was used to estimate trophic niche space of fish communities. Fish biomass did not differ between impaired and reference lakes despite substantial differences in potential diet. Fish depended strongly on littoral benthos in the reference lakes but consumed more pelagic food in the impaired lakes. The trophic niche of the focal, most common fish species (i.e., yellow perch, smallmouth bass, pumpkinseed and brown bullhead) was larger in the impaired lakes. We attributed these differences to low diversity at the highest trophic levels of fish communities in the impaired lakes as well as to depauperate benthic invertebrate communities. In contrast to the food webs of most temperate lakes, fish in impaired lakes preyed less on littoral invertebrates yet still managed to maintain a reference lake level of biomass standing crop by relying more on pelagic resources – macro zooplankton such as Chaoborus.  相似文献   

Non‐native rainbow trout (Oncorhynchus mykiss) occupy a different trophic niche to native Breede River redfin (Pseudobarbus burchelli) which they replace in South African headwater streams          下载免费PDF全文

Jeremy M. Shelton  Matthew S. Bird  Michael J. Samways  Jenny A. Day 《Ecology of Freshwater Fish》2017,26(3):484-496

Recent research has revealed that non‐native rainbow trout Oncorhynchus mykiss have largely replaced a native cyprinid, the Breede River redfin Pseudobarbus burchelli, as the dominant species of fish in many headwater streams in the Cape Floristic Region (CFR) of South Africa. Moreover, differences in the composition of benthic communities in CFR headwater streams with and without trout suggest that trout do not functionally compensate for the native redfin which they have replaced in these food webs. In this study, we used gut content and stable isotope analyses to characterise and compare the trophic niches and diet compositions of allopatric populations of trout and redfin in six CFR headwater streams (three containing trout, three containing redfin). Results indicate that native redfin exploit a broader trophic niche, and a more omnivorous diet, than do trout. Gut content analyses showed terrestrial invertebrates to be an important prey source for trout, which could potentially offset predation pressure on aquatic invertebrates and explain why benthic invertebrate density in streams with trout is higher than that in streams with no trout. Contrastingly, redfin diet appeared to be dominated by aquatic invertebrates, with terrestrial prey a less important food item in the guts of redfin. That redfin and trout exploit nonequivalent trophic niches may have consequences for benthic community composition in CFR headwater streams, and this study highlights the importance of quantifying how the functional role of predators changes following a predator replacement for understanding and managing the consequences of non‐native predator invasions.  相似文献   

Spatial and temporal patterns of vertical distribution for three planktivorous fishes in Lake Washington     

Thomas P. Quinn  David A. Beauchamp 《Ecology of Freshwater Fish》2012,21(3):337-348

Abstract – We sampled three limnetic fish species: juvenile sockeye salmon (Oncorhynchus nerka), three‐spine stickleback (Gasterosteus aculeatus) and longfin smelt (Spirinchus thaleichthys) in Lake Washington to quantify species‐specific patterns of diel vertical migration (DVM). Catch‐per‐unit‐effort data analysed from 15 years of midwater trawling documented seasonal and diel differences in vertical distributions for each species. These results were consistent with the hypothesis that the patterns of DVM in Lake Washington were affected by life history, size and morphology. Sockeye salmon showed clear DVM in spring but essentially no DVM in fall, remaining in deep water, whereas three‐spine sticklebacks were prevalent at the surface at night in both seasons. In fall, distribution patterns may be explained by differences in thermal performance (e.g., sticklebacks favouring warm water), but the patterns were also consistent with inter‐specific differences in predation risk. Younger sockeye salmon and longfin smelt were present in greater proportions higher in the water column during dusk and night periods than older conspecifics. Compared with sockeye salmon, the greater use by three‐spine sticklebacks of surface waters throughout the diel cycle during weak thermal stratification in spring was consistent with the hypothesis that sticklebacks’ armour reduces predation risk, but use of this warmer, metabolically beneficial stratum may also have promoted growth. This study illustrates variation in the vertical distribution of three sympatric planktivores and offers broader implications for the DVM phenomenon and applied lake ecology.  相似文献   

Geographical Distribution of African Mammals     

Jean Dorst 《African Zoology》2013,48(1):147-148

This is a report of a marine predator (the white shark) being threatened by a member of the species on which it preys (a male Cape fur seal). Although these events may be rarely observed or occur infrequently, they may have important implications for the predator and its prey.We suggest that shark mobbing by adult male Cape fur seals is adaptive for the reduction of risk of predation by sharks. Mobbing of sharks is likely to alert conspecifics to the presence of a predator, and/or reduce the shark's hunting motivation near the mobbing site.  相似文献   

膜肩网蝽的一种新天敌—异绒螨          下载免费PDF全文

赵玲  梁成杰 《林业科学研究》1989,2(1):42-46

异绒螨(Allotrombium sp.) 在北京、山东临沂地区每年发生一代,以成螨越冬。成螨和若螨可捕食膜肩网蝽(Hegesidemus habrus Drake)若虫,对膜肩网蝽种群数量有控制作用。异绒螨越冬前不产卵,翌年春产卵,幼螨营寄生生活。菜蚜是室内饲养异绒螨的好饲料,可缩短生活历期,有利于林间释放。在杨树幼林中,以若螨与膜肩网蝽1:50释放,膜肩网蝽虫口减退率达76.01％。人工助迁成螨,在林间亦易定居。  相似文献   

暴猎蝽形态特征和生物学特性的研究^*          下载免费PDF全文

姚德富  严静君  李广武  刘后平 《林业科学研究》1995,8(4):442-446

据在四川省大邑县和北京室内饲养观察，暴猎蝽１ａ发生一代，以５龄若虫越冬。卵期２７．０８±１．００ｄ。若虫共５龄，历期３３４．７５±４．３０ｄ。成虫羽化后１６～１８ｄ交配，交配后１８～１９ｄ开始产卵。描述了各虫态形态特征。记述了生物学特性。试验表明该虫是舞毒蛾、杨扇舟蛾、春尺蠖、北京杨锉叶蜂、柳毒蛾、刺槐蚜等多种林木害虫的捕食性天故。  相似文献