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1.
    
Plant establishment and growth on rocky outcrops in the Itatiaia massif (2400 m a.s.l.), southeastern Brazil, are limited by lack of soil and by freezing temperatures in winter nights. Mat‐forming species of different sizes and shapes on bare rock provide substrate for other plants to establish. The habitat preference of two geophytes, Stevia camporum (Asteraceae) and Alstroemeria foliosa (Alstroemeriaceae), was compared with regard to their association with the type of mat species and distinct rock topographies. The habitat preference of the mat species in regard to topography was also assessed. We found 1706 ramets of S. camporum and 1317 of A. foliosa in 253 vegetation islands ranging in size from 0.005 to 18.097 m2. Mat species in these islands were Fernseea itatiaiae, Vriesea itatiaiae (both Bromeliaceae), Pleurostima gounelleana (Velloziaceae) and/or Campylopus pilifer (Dicranaceae) and other mosses. Mat species were segregated by topography. Geophytes were similarly distributed across types of topography but showed negative interspecific association. S. camporum occurred mostly on the moss‐dominated islands, whereas A. foliosa was more common in P. gounelleana islands. We found geophyte co‐occurrence in larger vegetation islands containing both P. gounelleana and mosses as mat species. Thus, the effect of topography on geophyte segregation was indirect, since topography affects mat species distribution, and the geophyte preference for distinct mat species as substrate resulted in their segregation.  相似文献   

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African savannahs are characterised by a high plant diversity, partly resulting from a high turnover in community compositions across space. However, it is poorly understood what is driving this spatial turnover in plant communities. Here, we investigate to which extent the presence of rocky outcrops (also called kopjes) explains the community composition of trees in an African savannah, and how we can understand the responses of tree species to rocky outcrops by their functional traits. Along a precipitation gradient, we visited 24 sites in Serengeti National Park (Tanzania). At each site, we characterised tree communities, as well as their functional traits, in both a kopje and an adjacent open savannah plot (matrix plot). We found that kopjes harboured elevated tree abundances and species richness. Their dominant trees were more often evergreen, had a higher specific leaf area, a lower leaf nitrogen content and a lower spine density, than dominant trees in the savannah matrix. Differences in tree communities between kopjes and savannah matrix plots were generally the largest at sites with low precipitation. Our results indicate that kopjes are strong drivers of tree biodiversity, possibly due to locally increased soil moisture and low fire frequencies. The uniqueness of kopje tree communities may have important implications for higher trophic levels and ecosystem functioning.  相似文献   

4.
Summary We demonstrate that an egg parasitoid, Anagrus delicatus (Mymaridae, Hymenoptera) and its host, Prokelesia marginata (Delphacidae, Homoptera) regularly disperse 1 km or more in a north Florida saltmarsh. Anagrus delicatus were caught on yellow sticky traps on offshore islets and oyster bars throughout the spring, summer, and fall, whereas P. marginata were caught during one pulse in the spring. Parasitism rates were higher on offshore islets than at mainland sites, even though egg densities were higher at the mainland sites. The majority of parasitoids caught offshore were females. Long-distance dispersal by A. delicatus may be a cause of inverse density-dependent or density-independent spatial patterns of parasitism and may represent a risk-spreading strategy.  相似文献   

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To account for differences in occurrence of social behavior in different lineages of bees, Michener (1985) hypothesized that ground nests are more easily located by parasites than are twig nests. In the former case parasites search in two dimensions, while in the latter they search in three-dimensional space. One prediction derived from this hypothesis is that ground nests will have higher rates of parasitism than twig nests. A survey of published reports on rates of cell parasitism for 92 species of nesting bees and wasps (Apoidea) shows no significant differences in mean parasitism rates between these two classes of nests. The analyses were repeated at the generic level (N=44), yielding the same pattern. These data may be biased due to phylogenetic effects. Paired comparisons (n=11 pairs) of related taxa that differ in nest site show that ground-nesting taxa more often have higher rates of parasitism than twig-nesters. The use of artificial trap-nests to study twig-nesters significantly enhances the success rate of parasites. This bias, as well as several other limitations, suggests that experimental studies of the host-searching capabilities of parasites and predators may be more efficacious than such comparative tests.  相似文献   

7.
The dry weight, development, and feeding rates of Culex pipiens and Toxorhynchites amboinensis larvae infected with the nematode, Romanomermis culicivorax, were measured and gross conversion efficiences were calculated. The weight of C. pipiens larvae infected at two different inoculum levels did not differ significantly from controls until day 6 postinfection (PI). Infected larvae of T. amboinensis were significantly lighter than controls at days 2, 4, and 6 PI. The rate of larval mosquito development was slowed after day 3 in parasitized individuals of both mosquito species. Infection significantly retarded the interval feeding rate of the filter-feeding C. pipiens throughout development. Infected T. amboinensis larvae consumed significantly fewer prey larvae of C. pipiens than controls. Calculation of gross conversion efficiency (GCE) showed that lightly infected C. pipiens larvae had an elevated GCE early in the infection but were less efficient relative to controls after 4 days PI. Lightly parasitized T. amboinensis had a lower total GCE than controls.  相似文献   

8.
蒋华伟  方芳  郭水良 《生态学报》2008,28(1):399-406
调查发现,野外有日本菟丝子(Cuscutajaponica)寄生于加拿大一枝黄花(Sotidago canadensis)植株的现象,被寄生的加拿大一枝黄花植株矮小,叶片枯黄,生长严重受阻.在实验控制条件下,观测了日本菟丝子寄生后加拿大一枝黄花生理生态特性的相关指标,并对寄主进行了解剖观察,探讨了应用日本菟丝子防除加拿大一枝黄花的可行性.结果表明:(1)日本菟丝子可以寄生于加拿大一枝黄花的茎及叶片,寄生根能够穿过加拿大一枝黄花表皮、皮层直至髓部,从寄主植株吸收水分和养分,使自身生物量得到增加,并严重影响了寄主的生长;(2)寄生50-60d后,被寄生植株最大光合速率只有对照的58.81%,而光合补偿点则为对照的153.39%;脯氨酸和丙二醛含量分别为对照的2.88和1.29倍,可溶性蛋白、可溶性总糖含量则分别下降了43.45%、44.47%;(3)金华地区,自然条件下生长的加拿大一枝黄花一般在9月中旬现蕾,10月中旬进入盛花期,而被寄生植株直到10月下旬才开始现蕾,花序长度不到正常植株的10%,当菟丝子生物量(干重)超过加拿大一枝黄花植株的13.14%时该植株不能开花结实.从实验结果看,日本菟丝子寄生可以严重影响加拿大一枝黄花的营养生长和开花结实.因此,利用日本菟丝子有望成为防治加拿大一枝黄花危害的一种辅助手段.  相似文献   

9.
Fleming  T. H.  Venable  D. L.  Herrera  L. G. M. 《Plant Ecology》1993,107(1):107-120
Plant Ecology - In this paper we address two questions concerning the interaction between fleshy-fruited plants and their seed dispersers: (1) What determines optimal disperser coterie size...  相似文献   

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1. Dispersal is essential for locating mates, new resources, and to escape unfavourable conditions. Parasitism can impact a host's ability to perform energetically demanding activities such as long‐distance flight, with important consequences for gene flow and meta‐population dynamics. 2. Ectoparasites, in particular, can adversely affect host flight performance by diminishing flight aerodynamics and/or by inflicting physiological damage while feeding on host tissue. 3. Experimental flight assays were conducted using two fruit fly‐mite systems: Drosophila nigrospiracula (Patterson and Wheeler) – Macrocheles subbadius (Berlese) and D. hydei (Sturtevan) – M. muscaedomesticae (Scopoli). Flies that are burdened by mites are expected to exhibit lower flight endurance compared to uninfected flies. 4. The results show that the presence of mites (attached) significantly decreased flight endurance by 57% and 78% compared to uninfected D. nigrospiracula and D. hydei, respectively. The physiological damage caused by M. subbadius was revealed through a 53% decline in flight time among previously infected flies (mites removed just prior to flight assay). Surprisingly, the presumably phoretic M. muscaedomesticae also caused a 62% reduction in flight endurance among previously infected D. hydei. 5. These results suggest a strong deleterious effect of ectoparasitic mites on host flight performance, mediated by a reduction in flight aerodynamics and damage to host physiology. Adverse effects on host flight and/or dispersal may have broad implications for gene flow, population genetic structure, and local adaptation in both host and parasite meta‐populations.  相似文献   

11.
Summary A new system of dispersal units has been elaborated, based on weight and morphological features functional in dispersal. Weight was divided into eight classes and the functional morphological features were selected in such a way that their effectiveness could be tested by experiments.The spectra of weight and dispersal adaptations of dispersal units sampled in Euphorbio-Pinetum nigrae and Fumano-Stipetum habitats south of Vienna are calculated with this system and then compared.The results show that both communities can be characterized with such spectra. It is also possible with these spectra to make statements about the ecological and social position of the association in a succession.Nomenclature follows Ehrendorfer (1973).  相似文献   

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Two possible patterns of bias in primary sex ratio have been proposed for size‐dimorphic brood parasites that do not evict host chicks: (1) larger males should be laid at greater frequency in hosts larger than the parasite because they compete better (increasing their survival) than females with large host nest‐mates, and (2) more costly males (i.e. the larger sex) should be laid at greater frequency in hosts smaller than the parasite because, in these hosts, parasite nestlings are provisioned at a higher rate and grow faster than in larger hosts. We tested these hypotheses in two hosts of the sexually size‐dimorphic shiny cowbird, Molothrus bonariensis, one smaller (house wren, Troglodytes aedon) and one larger (chalk‐browed mockingbird, Mimus saturninus) than the parasite. We measured: (1) sex ratio at laying; (2) development of sexual differences in body mass during the nestling stage; and (3) chick survival and sex ratio of chicks before fledging. In both hosts, we found sexual differences in body mass of nestlings from 7 days of age onwards, although we did not find a bias in the sex ratio of eggs laid and chicks fledged. The results of the present study do not support the hypothesis that shiny cowbird females benefit from biasing the primary sex ratio depending on the size of the hosts they parasitize. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 442–448.  相似文献   

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Marine rocky outcrops are model systems of community assembly under harsh conditions. The prevailing environmental conditions that determine a coast–inland gradient of stress and disturbance impose a strong environmental filter on community assembly. However, the Atlantic rocky outcrops of Uruguay challenge this assumption as they exhibit high plant diversity at small spatial scales. We investigated this study system to answer: (1) which environmental factors determine diversity at the local scale; (2) and how does the regional pool influence species composition along the coast–inland gradient?  相似文献   

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散布和繁殖是目前植物进化生物学研究的热点之一。散布对植物的进化过程,如地理分布格局、物种形成等具有重要的影响。本文对植物散布过程中涉及到的各种因素如散布体及其数量和寿命,散布机制进行了系统的总结,并对散布体与各种散布机制之间的适应关系作了分析。  相似文献   

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1. Trade-offs are often predicted to occur between energetically costly activities, such as somatic growth and eliciting immune responses to parasites. Although parasitism frequently reduces growth via lowered consumption, it remains unclear if the energetic demands of generating immune responses also affect the digestive physiological processes necessary for growth. Moreover, as local environmental conditions affect energetic investment towards growth and immune responses, the extent of any digestive–immune response trade-offs may vary among populations and not be fixed at the species-level. 2. To test these ideas, melanisation – a general innate immune response – was first induced in damselfly larvae (Enallagma vesperum) from two populations. The study then quantified growth and consumption rates, assimilation and production efficiencies, and daily metabolic rates to determine if digestive–immune response trade-offs were present and, if so, whether they differed between populations. 3. There was no evidence of any trade-offs between immune responses and digestive physiology components in either population. However, the results did show that populations differentially allocated energy towards different digestive physiology components after an immune response was elicited: one population increased their relative consumption and daily metabolic rates, while the other population had lower assimilation efficiencies and consumption rates. 4. Although researchers lack a mechanistic understanding of the observed population-level differences, these results suggest that accounting for population-level variation in digestive physiology and immune responses is critical to inferences about how immunological defences to parasitism may affect the ability for organisms to both acquire and utilise resources.  相似文献   

16.
    
As solitary nymphal parasitoids of Pamtrioza sinica,the ectoparasitoid Tamarixia lyciumi and the endoparasitoid Psyllaephagus arenarius act as effective biocontrol agents.Thus,it is necessary to facilitate mass productions of both species.Despite showing an excellent parasitic ability,Ps.arenarius is often trapped fatally inside 5th-instar nymphs of Pa.sinica due to strong host immunity.To improve the emergence rate of Ps.arenarius,we evaluated whether Ps.arenarius could utilize T.lyciumi venom via multiparasitism,so the parasitism characteristics of both species were examined between separate-existence(monoparasitism only)and co-existence(mono-and multiparasitism)systems.Further,the parasitism characteristics of Ps.arenarius on venom-injected hosts with/without T.lyciumi eggs were tested to further identify the facilitator.The results showed the parasitism rate of T.lyciumi was increased while that of Ps.arenarius did not change from separate-existence to co-existence systems.The intrinsic performances of two species in monoparasitism did not differ between separate-and co-existence systems.From monoparasitism(separate-existence)to multiparasitism(co-existence),no differences were detected in the intrinsic performances of T.lyciumi,but those of Ps.arenarius were greatly improved.After T.lyciumi venom injection,the parasitism characteristics of Ps.arenarius did not differ between venom-injected hosts with T.lyciumi eggs and those without,further indicating Ps.arenarius benefited from the venom of T.lyciumi females rather than T.lyciumi egg/larval secretions.Instead of negative effects,multiparasitism with ectoparasitoids improves endoparasitoids due to ectoparasitic venom.The study increases host resource utilization and provides creative ways for mass production of endoparasitoids.  相似文献   

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Following nest destruction, the laying of physiologically committed eggs (eggs that are ovulated, yolked, and making their way through the oviduct) in the nests of other birds is considered a viable pathway for the evolution of obligate interspecific brood parasitism. While intraspecific brood parasitism in response to nest predation has been experimentally demonstrated, this pathway has yet to be evaluated in an interspecific context. We studied patterns of egg laying following experimental nest destruction in captive zebra finches, Taeniopygia guttata, a frequent intraspecific brood parasite. We found that zebra finches laid physiologically committed eggs indiscriminately between nests containing conspecific eggs and nests containing heterospecific eggs (of Bengalese finches, Lonchura striata vars. domestica), despite the con‐ and heterospecific eggs differing in both size and coloration. This is the first experimental evidence that nest destruction may provide a pathway for the evolution of interspecific brood parasitism in birds.  相似文献   

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方笛熙  万霞  毛婉琼  张锋 《生态学报》2023,43(17):7109-7117
病原体感染对种间竞争的影响可能是因为改变了宿主的资源利用过程,然而竞争模型(Lotka-Volterra)由于参数化竞争系数而忽略了资源的动态变化过程,因此基于此类模型的研究无法揭示病原体对宿主资源利用的影响。基于Tilman的资源竞争理论构建了病原体感染一个物种的资源竞争模型,通过分析宿主物种资源利用效率的变化探讨了病原体对种间竞争的影响。结果表明:(1)病原体降低了宿主对资源的消耗率(消费矢量变短),抬高了对资源的最低需求(零等倾线上移),这意味着宿主的竞争力减弱;(2)虽然感染影响了竞争物种的密度,但不会改变共存物种的共存状态;(3)病原体可以使宿主物种的竞争对手更容易入侵,形成共存局面,极大地扩大了竞争物种共存的参数范围,本质上促进了物种多样性维持;(4)病原体的传播率和毒性也复杂地影响了竞争物种共存,传播率越大越能促进物种共存,而中等强度毒性最能促进物种共存。研究结果明确了病原体对物种资源利用模式的潜在改变,强调了病原体在物种共存和生物多样性维持中的重要性。  相似文献   

19.
Norton et al. (2006) compared "handaxes" from Korea and two basins with Acheulean assemblages (Olorgesailie, Kenya and Hunsgi-Baichbal, India). The authors found significant morphological variance between Eastern and Western handaxes, leading them to conclude that East Asian tool forms were not morphologically similar to typical Acheulean implements. We test this finding using a larger array of localities, and find some metrical overlaps between handaxes and cleavers in the West and East. We indicate the role of convergence in lithic assemblage formation, but we also raise the possibility that handaxes and cleavers in the Luonan Basin (China) may represent evidence for Acheulean stone tool manufacturing methods.  相似文献   

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