Search results for "DIFFERENTIATION"
showing 10 items of 1605 documents
Dietary divergence in space and time – Lessons from the dwarf-goat Myotragus balearicus (Pleisto-Holocene, Mallorca, Spain)
2013
8 pages; International audience; Newly colonised, isolated habitats, like islands, provide diverse niches to be filled and are prone to facilitate ecological separation which might lead to an adaptive radiation. Examples of such radiations can be found in the Mediterranean for the genera Candiacervus (Crete), Nesogoral (Sardinia) and Hoplitomeryx (Gargano). A different strategy to cope with limited resources on islands is generalism. We test whether populations of the endemic bovid Myotragus balearicus from two sites and Pleistocene as well as Holocene levels on Mallorca island displays ecological separation indicated by diet, or whether the species shifted its dietary trait towards general…
Geographic variability of ecological niches of plant species: are competition and stress relevant?
2002
A species’ niche position may differ strongly between geographic regions, for instance due to the effect of competitors or ecophysiological stress. However, it is unclear whether such strong geographic niche variation is the rule or the exception. We compared the niche positions of plant species between central England and eastern central Europe (as available from the literature), using phylogenetically independent contrasts. We found that most species occupied similar niche positions in both regions. More importantly, we found that niche variation was not higher in species susceptible to competitive displacement. Nor was niche variation higher in species that reach the edge of their range …
Resource competition between sympatric sibling rotifer species
2001
Mechanisms underlying competitive interactions are important in understanding the structure of planktonic communities, particularly the coexistence of similar species. Here we present experimental results of exploitative competition among three sympatric sibling species of the Brachionus plicatilis complex for two differently-sized species of food microalgae. These three rotifer species are to be found in seasonal succession in brackish ponds on the Spanish Mediterranean coast; they can, however, co-occur for long periods. The functional and numerical responses of the three Brachionus species to both food microalgae, although similar, differed. Neither rotifer population growth nor grazing …
Pool choice in a vertical landscape: tadpole rearing site flexibility in phytotelm-breeding frogs
2021
AbstractMany species of Neotropical frogs have evolved to deposit their tadpoles in small water bodies inside plant structures called phytotelmata. These pools are small enough to exclude large predators but have limited nutrients and high desiccation risk. Here, we explore phytotelm use by three common Neotropical species: Osteocephalus oophagus, an arboreal frog that periodically feeds eggs to its tadpoles; Dendrobates tinctorius, a tadpole-transporting poison frog with cannibalistic tadpoles; and Allobates femoralis, a terrestrial tadpole-transporting poison frog with omnivorous tadpoles. We found that D. tinctorius occupies pools across the chemical and vertical gradient, whereas A. fem…
Dinner with the roommates: trophic niche differentiation and competition in a mutualistic ant‐ant association
2020
1. The potential for competition is highest among species in close association. Despite net benefits for both parties, mutualisms can involve costs, including food competition. This might be true for the two neotropical ants Camponotus femoratus and Crematogaster levior, which share the same nest in a presumably mutualistic association (parabiosis). 2. While each nest involves one Crematogaster and one Camponotus partner, both taxa were recently found to comprise two cryptic species that show no partner preferences and seem ecologically similar. Since these cryptic species often occur in close sympatry, they might need to partition their niches to avoid competitive exclusion. 3. Here, we in…
Simultaneity between strategic variables: Production, innovation, and product differentiation
1995
This paper aims to analyze the existence of simultaneous effects among the variables production, product differentiation, and innovation. Microeconomic data from a sample of 2,160 firms are used as a base. Empirical results show that a positive correlation exists from innovation to product differentiation, thus showing that it is in the process of production itself, through technical improvements, where product differentiation is determined. On the other hand, no positive effect exists from product differentiation to innovation, i.e., once technical improvements have been established, firms exchange the barriers to entry created by brand image for the real barriers established by innovation…
How endogenous asymmetries in interregional market access trigger regional divergence
2005
We investigate how asymmetric trade patterns in differentiated products affect the regional distribution of economic activities. The asymmetry in interregional market access is an endogenous result of price competition and industry location and arises for intermediate values of trade costs. We show that the emergence of one-way trade in differentiated products gives rise to strong agglomeration forces and leads to the absorption of the smaller region's industry by the larger region. The number of spatial equilibria increases once the pattern of trade is endogenously accounted for. (c) 2004 Elsevier B.V. All rights reserved.
Alternative pricing regimes in interurban passenger transport with externalities and modal competition
2009
Abstract We develop an interurban passenger transport model with modal competition, where modes are perceived as differentiated products, and capture all major externalities. Our objective is to establish whether alternative regulatory regimes, which may involve road tolls, may lead to a traffic allocation, user welfare, and total welfare that may be closer to the social optimum. An empirical application to interurban Spanish travel is undertaken. We find that the private regime yields the lowest total welfare level: 12.6% below the social optimum level. Optimum pricing requires a toll on car transport of 5.1 cents of per passenger-km, and a price decrease of all other modes, relative to th…
Quality pricing-to-market
2014
We examine firm's pricing-to-market decisions in vertically differentiated industries featuring a large number of firms that compete monopolistically in the quality space. Firms sell goods of heterogeneous quality to consumers with non-homothetic preferences that differ in their income and thus their marginal willingness to pay for quality increments. We derive closed-form solutions for the pricing game under costly international trade, thus establishing existence and uniqueness. We then examine how the interaction of good quality and market demand for quality affects firms' pricing-to-market decisions. The relative price of high quality goods compared to that of low quality goods is an inc…
Stable isotope analysis of well-preserved 120,000-year-old herbivore bone collagen from the Middle Palaeolithic site of Neumark-Nord 2, Germany revea…
2012
Abstract Herbivores from the Neumark-Nord 2 archaeological site, Germany, were analysed for bone collagen stable carbon (δ 13 C) and nitrogen (δ 15 N) isotope ratios in order to investigate feeding ecology at this early Last Interglacial (Eemian) shallow-lake site. Of 42 faunal samples selected, 23 yielded collagen, demonstrating remarkable preservation for material of this age. The results indicate clear inter-specific differences in δ 15 N and δ 13 C values, notably between equids ( Equus ) and bovids ( Bos/Bison ), with mean difference Δ 15 N of + 2‰ measured in the bovids compared to the equids. The potential reasons for these differences are explored, including physiology, herbivore fe…