Search results for "Reproduction"
showing 10 items of 752 documents
Corporate Reputation and the Theory of Social Capital
2013
Seasonal dynamics of egg laying and egg-laying strategy of the ectoparasite Argulus coregoni (Crustacea: Branchiura).
2004
Substrate preferences, spatial aggregation patterns and seasonal dynamics in the egg laying of ectoparasiticArgulus coregoniwere studied at a commercial fish farm in Finland. Pilot experiments showed thatA. coregonifemales selected specific types of substrates for egg laying. Significantly moreA. coregonieggs were laid on dark substrates than on light ones suggesting the use of visual cues. Therefore, egg-laying plates of dark colour were constructed for further experiments. MostA. coregonieggs were deposited in locations in shadow and in the deepest water in a 2 m deep farming canal. Relatively more eggs were laid on bottom stones situated near each egg-laying trap than on artificial egg-l…
Response of an arctic predator guild to collapsing lemming cycles
2012
6 pages; International audience; Alpine and arctic lemming populations appear to be highly sensitive to climate change, and when faced with warmer and shorter winters, their well-known high-amplitude population cycles may collapse. Being keystone species in tundra ecosystems, changed lemming dynamics may convey significant knock-on effects on trophically linked species. Here, we analyse long-term (1988-2010), community-wide monitoring data from two sites in high-arctic Greenland and document how a collapse in collared lemming cyclicity affects the population dynamics of the predator guild. Dramatic changes were observed in two highly specialized lemming predators: snowy owl and stoat. Follo…
Fluctuating asymmetry in bank vole populations (Rodentia, Arvicolinae) reflects stress caused by landscape fragmentation in the Mont-Saint-Michel Bay
2003
In intensively farmed, reclaimed areas (polders) of Mont-St-Michel Bay, France, bank voles (Clethrionomys glareolus) live in fragmented hedgerows, where populations are small and dispersal rates and genetic diversity are low. These small populations are likely to have been exposed to potential environmental and/or genetic stress. The sensitivity of development to stress can be measured by fluctuating asymmetry (FA). FA was calculated for three samples from a disturbed area and one sample from an adjacent, more connected and undisturbed landscape. Size FA was estimated from 16 measurements of the skull and teeth whilst shape asymmetry was estimated from the skull alone. Bank voles in fragmen…
Human impact diminishes seedling species richness in Kakamega Forest, Kenya
2008
Summary Anthropogenic forest fragmentation and other kinds of human disturbance, such as selective logging, can reduce the diversity of plant and animal species. To evaluate the impact of fragmentation and small-scale disturbance on forest regeneration, we assessed species richness and total abundance of adult trees in comparison with seedlings in the heavily fragmented and disturbed Kakamega Forest, western Kenya. In nine differently disturbed 1-ha study blocks distributed across the main forest and fragments, we mapped all trees >10 cm in diameter at breast height. Additionally, we established ninety 1-m 2 seedling plots within these 1-ha study blocks which were monitored over 2.5 years. …
Fragmentation and local disturbance of forests reduce frugivore diversity and fruit removal in Ficus thonningii trees
2008
Clearance, fragmentation, and degradation of tropical forests have resulted in declines of biodiversity. This loss of biodiversity is endangering important ecosystem processes such as seed dispersal. If anthropogenic disturbances affect seed dispersal of keystone plants, effects on tropical ecosystems might be especially pronounced. We studied frugivore assemblages and fruit removal from 25 Ficus thonningii trees in the heavily fragmented and disturbed Kakamega Forest, western Kenya. During 400 observation hours we recorded 36 frugivores visiting F. thonningii trees. We recorded significantly fewer frugivorous species in fragments compared to the main forest and in highly, compared to littl…
Flowering and fruiting phenology and breeding system ofCistus albidusL.
1995
Summary The flowering and fruiting phenology and breeding system of Cistus albidus L. are studied. Four phases are established for the development of the flower, which remains open for a period of less than 14hrs, although this time—span can be further reduced if environmental conditions are unfavourable. Only 65.6 % flowers develop ripe fruits, the greatest losses occurring in the change from flower to unripe fruit. H is a xenogamous species with a PAD ratio of 5.426 ±816. Experimentally, fruits may be formed by autogamy through manual pollination, although this does not occur spontaneously. There is recognition by the plant of its own pollen tube, which reduced the production of fruits by…
Polymorphism in Developmental Mode and Its Effect on Population Genetic Structure of a Spionid Polychaete, Pygospio elegans
2012
Population genetic structure of sedentary marine species is expected to be shaped mainly by the dispersal ability of their larvae. Long-lived planktonic larvae can connect populations through migration and gene flow, whereas species with nondispersive benthic or direct-developing larvae are expected to have genetically differentiated populations. Poecilogonous species producing different larval types are ideal when studying the effect of developmental mode on population genetic structure and connectivity. In the spionid polychaete Pygospio elegans, different larval types have been observed between, and sometimes also within, populations. We used microsatellite markers to study population st…
Bilateral Monopoly: A Contribution by Francesco Ferrara
2009
In this paper, we propose an interpretation of the application of "cost of reproduction" of Francesco Ferrara to the exchange between two agents to highlight its relevance for the theory of bilateral monopoly. In the Teoria delle Mercedi (1863), Ferrara gives a numerical example to explain price determination in the exchange between one buyer and one seller. Here, this example is translated into a mathematical model that reproduces the fundamental issues of the neoclassical debate on the indeterminacy of price in the Cournot model (1938), and anticipates the solutions proposed by Edgeworth (1881) at the end of this debate.