			Home About us Contact

Different Ecological Conditions (different + ecological_condition)

Distribution by Scientific Domains

Life Sciences	75%

Selected Abstracts

Experimental Study on the Diet of Mosquitofish (Gambusia holbrooki) under Different Ecological Conditions in a Shallow Lake

INTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 3 2004
Saúl Blanco
Abstract We studied the diet of the eastern mosquitofish Gambusia holbrooki with in situ experimental mesocosms located in a shallow lake. Different nutrient concentrations (phosphorus and nitrogen) and fish population densities were tested. Our results confirm that it is a planktivorous species, with also a great ingestion of algae and detritus. Nutrient fertilization caused almost no changes in this species feeding behavior, but larger mosquitofish stocks induced a shift to zooplanktivory and a decline in detritivory. When macrophytes were present, the predation effect focused on zooplankton and plant-associated animals, otherwise predation on bottom macroinvertebrates increased. Females preyed upon almost all groups more intensely, including detritus. Males and juveniles did not overlap diet, the former being more selective on ostracods, while juveniles consumed detritus, rotifers and cladoceran. Our data support the idea that mosquitofish can cause important top-down effects in shallow lakes under a wide variety of ecological conditions, being an important zooplanktivore in both turbid and plant-dominated shallow lakes especially in the Mediterranean zone, where high temperatures and absence of piscivores promote maintenance of its populations during the whole year. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Racial Differences in Division of Labor in Colonies of the Honey Bee (Apis mellifera)

ETHOLOGY, Issue 2 2002
Charles Brillet
We measured the age at onset of foraging in colonies derived from three races of European honey bees, Apis mellifera mellifera, Apis mellifera caucasica and Apis mellifera ligustica, using a cross-fostering design that involved six unrelated colonies of each race. There was a significant effect of the race of the introduced bees on the age at onset of foraging: cohorts of A. m. ligustica bees showed the earliest onset, regardless of the race of the colony they were introduced to. There also was a significant effect of the race of the host colony: cohorts of bees introduced into mellifera colonies showed the earliest onset of foraging, regardless of the race of the bees introduced. Significant inter-trial differences also were detected, primarily because of a later onset of foraging in trials conducted during the autumn (September,October). These results demonstrate differences among European races of honey bees in one important component of colony division of labor. They also provide a starting point for analyses of the evolution of division of labor under different ecological conditions. [source]

Geographical variation in the size of body organs in seabirds

FUNCTIONAL ECOLOGY, Issue 3 2000
G. M. Hilton
Abstract 1.,The size of body organs shows adaptive temporal variation in many animal species. The variation in the size of body organs was examined to see if it is also a component of local adaptation to geographical variation in ecological conditions. 2.,Major body organs were measured in five species of Icelandic seabirds, sampled from two areas where birds experience slightly different ecological conditions. Between-area differences in ecological conditions were consistent among the study species, allowing tests of the generality of ecological effects on organ size. 3.,All major body organs showed geographical size variation. Livers and kidneys were larger in locations where daily energy expenditure was expected to be higher; small intestines were heavier where food was of lower energy density; stomachs were heavier where food was less digestible; heart and flight muscle were larger where flight costs were greater. 4.,It is concluded that adaptive variation in organ size may be an important means by which animals optimize exploitation of their local environment, and may be a proximate factor in intraspecific life-history and metabolic variations between geographically separate populations. [source]

Satellite species in lampreys: a worldwide trend for ecological speciation in sympatry?

JOURNAL OF FISH BIOLOGY, Issue 2 2003
V. Salewski
Amongst several theories of speciation, sympatric speciation has been the most controversial but it is now widely accepted that populations can become reproductively isolated without being separated geographically. One problem with the acceptance of the theory of sympatric speciation, however, has been the lack of supporting empirical data and it is still believed that geographical isolation is responsible for the majority of speciation events. Here the example of species pairs in lampreys suggests that sympatric speciation in a whole taxonomic group could occur throughout its worldwide range. Lampreys occur in two ecologically distinct forms: parasitic mostly anadromous species that forage on tissue and body fluids of host fishes, and non-parasitic forms that, apart from a short adult life when they cease feeding, spend their entire life as filter feeders in the substratum of stream beds. Both forms occur in sympatric species pairs throughout the range of lampreys that occur in Eurasia, North America and Australia and it is widely acknowledged that non-parasitic forms derive from parasitic forms. The larvae of both forms can be distinguished by their potential fecundity and therefore, it is argued that the mode of life is not a consequence of different ecological conditions. Furthermore, as lampreys prefer to choose mates of similar sizes and fertilization success decreases with increasing difference in body size, there is a strong disruptive selection between the two forms and they are therefore reproductively isolated. Besides theoretical aspects, the similarity of the species pairs, together with their occurrence in sympatry, the occurrence of forms with intermediate characteristics, and examples where speciation might be in progress, hints at the possibility that speciation also occurred in sympatry. The difference between lampreys and other examples of sympatric speciation is that there seems to be a trend towards sympatric speciation events throughout the worldwide range of lampreys which is neither restricted to relatively small localities nor caused by human disturbance. Species pairs in lampreys therefore offer a unique possibility of studying the process of sympatric speciation on a large scale. [source]