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Jennifer U M Jarvis - One of the best experts on this subject based on the ideXlab platform.
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a comparison of the ecology of two populations of the common mole rat cryptomys hottentotus hottentotus the effect of aridity on food foraging and body mass
Oecologia, 2000Co-Authors: A C Spinks, Nigel C Bennett, Jennifer U M JarvisAbstract:The aridity food distribution hypothesis (AFDH) maintains that ecological constraints in arid habitats curtail dispersal and promote the evolution of cooperative foraging social groups within the African mole-rats. To evaluate the validity of the AFDH, we investigated inter-habitat differences in food resource characteristics, foraging behaviour, colony size and individual body mass in two common mole-rat populations, one from a mesic and one from an arid habitat. Although food was clumped at both localities, the geophyte density was lower at the arid site. However, Geophytes from the arid site were larger than those from the mesic region, and this is suggested to compensate for the reduced geophyte density, enabling colonies to meet their energy requirements. Differences in food resource characteristics in turn influenced the pattern of foraging, the burrow systems at the arid site being longer and more linear than those from the mesic site. Mean colony size did not differ between the two sites, but animals from the arid site exhibited a reduced individual mass relative to those from the mesic area, probably an adaptation to reduce total colony energy expenditure given the elevated foraging costs in arid environments. The common mole-rat from the arid localities should occur in larger colonies than their mesic counterparts. The results from this investigation do not support this contention.
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foraging in wild and captive colonies of the common mole rat cryptomys hottentotus hottentotus rodentia bathyergidae
Journal of Zoology, 1999Co-Authors: A C Spinks, Nigel C Bennett, Trevor A Branch, Shula Croeser, Jennifer U M JarvisAbstract:The foraging behaviour of wild and captive colonies of the common mole-rat Cryptomys hottentotus hottentotus was investigated. Field studies were undertaken at Steinkopf, an arid site in the Northern Cape, South Africa. The resource biomass and the total available energy here were amongst the highest recorded for any bathyergids, but Geophytes were sparse and widely distributed. The low probability of locating these widely dispersed resources should promote co-operative foraging in these mole-rats. All common geophyte species were consumed, probably because high burrowing costs favour dietary generalism. The mole-rat biomass per metre of burrow system (0.5 ‐1.5 g.m -1 ) remains the lowest of any subterranean mammal. Burrow depths and diameters were positively correlated to the average mass of the mole-rats in each colony, apparently minimizing energetic costs and maximizing foraging success. Bulbs were stored in central food caches, and both field and laboratory data indicated size-based selectivity in their storage and consumption. As predicted by central place foraging theory, large bulbs were preferentially stored, and small bulbs preferentially consumed. However, factors other than energetic considerations may also influence these storage decisions. Total consumption time of bulbs was negatively correlated to animal size, and furthermore smaller bulbs were consumed more rapidly than larger ones. In addition to Geophytestoring, C. h. hottentotus also exhibited an alternative foraging strategy, termed ‘geophyte farming’, in which large bulbs were left and eaten in situ, and served as a renewable resource. Together with these foraging specializations, the evolution of sociality in mole-rats is a key factor which enables them to live in some of the most formidable habitats in Africa.
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food availability and foraging by wild colonies of damaraland mole rats cryptomys damarensis implications for sociality
Oecologia, 1998Co-Authors: Jennifer U M Jarvis, A C SpinksAbstract:We investigated some of the ecological determinants of sociality in the Damaraland mole-rat, including the spatial distribution and biomass of resources (Geophytes) available to foraging Damaraland mole-rats in partly vegetated sand dunes in the Kalahari and in grasslands near Dordabis, Namibia, and the foraging behaviour and residency characteristics of colonies at Dordabis. In both study areas, the Geophytes had a clumped distribution, but the highest coefficients of dispersion and mean biomass occurred in the Kalahari where the principal food was the gemsbok cucumber. However, because the coefficient of digestibility was lower in Geophytes from the Kalahari than from Dordabis, and the mole-rats only ate about half of a gemsbok cucumber, there was less energy available to mole-rats in the Kalahari. At Dordabis, large established colonies occur in the areas with the richest resources and remain resident in the same area for many years; within this area they search (blindly) for food during brief periods when the soil, at burrow depth, is moist and easily worked. Initially, long straight burrows are dug and few bulbs are taken; once the soil dries, minor changes are made to the burrow system as the mole-rats exploit the food patches they located immediately after the rain. Our results show that the characteristics of the resources, and the short time interval during which location of new resources is possible, favour group living; however, the constraints imposed by these features affect large and small colonies in different ways. Small colonies are more likely to fail than large ones and some crucial factors in the survival of these newly formed colonies are the richness of the area in which their burrows are located, and the size of the colony work force available to locate the food.
A C Spinks - One of the best experts on this subject based on the ideXlab platform.
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a comparison of the ecology of two populations of the common mole rat cryptomys hottentotus hottentotus the effect of aridity on food foraging and body mass
Oecologia, 2000Co-Authors: A C Spinks, Nigel C Bennett, Jennifer U M JarvisAbstract:The aridity food distribution hypothesis (AFDH) maintains that ecological constraints in arid habitats curtail dispersal and promote the evolution of cooperative foraging social groups within the African mole-rats. To evaluate the validity of the AFDH, we investigated inter-habitat differences in food resource characteristics, foraging behaviour, colony size and individual body mass in two common mole-rat populations, one from a mesic and one from an arid habitat. Although food was clumped at both localities, the geophyte density was lower at the arid site. However, Geophytes from the arid site were larger than those from the mesic region, and this is suggested to compensate for the reduced geophyte density, enabling colonies to meet their energy requirements. Differences in food resource characteristics in turn influenced the pattern of foraging, the burrow systems at the arid site being longer and more linear than those from the mesic site. Mean colony size did not differ between the two sites, but animals from the arid site exhibited a reduced individual mass relative to those from the mesic area, probably an adaptation to reduce total colony energy expenditure given the elevated foraging costs in arid environments. The common mole-rat from the arid localities should occur in larger colonies than their mesic counterparts. The results from this investigation do not support this contention.
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foraging in wild and captive colonies of the common mole rat cryptomys hottentotus hottentotus rodentia bathyergidae
Journal of Zoology, 1999Co-Authors: A C Spinks, Nigel C Bennett, Trevor A Branch, Shula Croeser, Jennifer U M JarvisAbstract:The foraging behaviour of wild and captive colonies of the common mole-rat Cryptomys hottentotus hottentotus was investigated. Field studies were undertaken at Steinkopf, an arid site in the Northern Cape, South Africa. The resource biomass and the total available energy here were amongst the highest recorded for any bathyergids, but Geophytes were sparse and widely distributed. The low probability of locating these widely dispersed resources should promote co-operative foraging in these mole-rats. All common geophyte species were consumed, probably because high burrowing costs favour dietary generalism. The mole-rat biomass per metre of burrow system (0.5 ‐1.5 g.m -1 ) remains the lowest of any subterranean mammal. Burrow depths and diameters were positively correlated to the average mass of the mole-rats in each colony, apparently minimizing energetic costs and maximizing foraging success. Bulbs were stored in central food caches, and both field and laboratory data indicated size-based selectivity in their storage and consumption. As predicted by central place foraging theory, large bulbs were preferentially stored, and small bulbs preferentially consumed. However, factors other than energetic considerations may also influence these storage decisions. Total consumption time of bulbs was negatively correlated to animal size, and furthermore smaller bulbs were consumed more rapidly than larger ones. In addition to Geophytestoring, C. h. hottentotus also exhibited an alternative foraging strategy, termed ‘geophyte farming’, in which large bulbs were left and eaten in situ, and served as a renewable resource. Together with these foraging specializations, the evolution of sociality in mole-rats is a key factor which enables them to live in some of the most formidable habitats in Africa.
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food availability and foraging by wild colonies of damaraland mole rats cryptomys damarensis implications for sociality
Oecologia, 1998Co-Authors: Jennifer U M Jarvis, A C SpinksAbstract:We investigated some of the ecological determinants of sociality in the Damaraland mole-rat, including the spatial distribution and biomass of resources (Geophytes) available to foraging Damaraland mole-rats in partly vegetated sand dunes in the Kalahari and in grasslands near Dordabis, Namibia, and the foraging behaviour and residency characteristics of colonies at Dordabis. In both study areas, the Geophytes had a clumped distribution, but the highest coefficients of dispersion and mean biomass occurred in the Kalahari where the principal food was the gemsbok cucumber. However, because the coefficient of digestibility was lower in Geophytes from the Kalahari than from Dordabis, and the mole-rats only ate about half of a gemsbok cucumber, there was less energy available to mole-rats in the Kalahari. At Dordabis, large established colonies occur in the areas with the richest resources and remain resident in the same area for many years; within this area they search (blindly) for food during brief periods when the soil, at burrow depth, is moist and easily worked. Initially, long straight burrows are dug and few bulbs are taken; once the soil dries, minor changes are made to the burrow system as the mole-rats exploit the food patches they located immediately after the rain. Our results show that the characteristics of the resources, and the short time interval during which location of new resources is possible, favour group living; however, the constraints imposed by these features affect large and small colonies in different ways. Small colonies are more likely to fail than large ones and some crucial factors in the survival of these newly formed colonies are the richness of the area in which their burrows are located, and the size of the colony work force available to locate the food.
Petr Pysek - One of the best experts on this subject based on the ideXlab platform.
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plant invasions in the czech republic current state introduction dynamics invasive species and invaded habitats
Preslia, 2012Co-Authors: Petr Pysek, Milan Chytrý, Jan Pergl, Jiři Sadlo, Jan WildAbstract:The Czech Republic has a strong tradition of research on synanthropic and alien plants, both historically and recently,which results in a good knowledge of alien flora and invasion patterns. In this paper the currect situation of plant invasions in the country is reviewed from the viewpoint of the composition of the country’s alien flora (based on a recently published checklist of alien taxa) and that of the level of habitat invasions, expressed as the proportion of alien species among all species recorded, and large-scale patterns of invasions in landscapes. At present there are 1454 alien taxa recorded in the national flora, consisting of 350 archaeophytes, introduced since the beginning of Neolithic agriculture until the end of theMedieval Period, and 1104 neophytes, introduced in theModern Period. In the last two centuries there was a steady increase in the number of alien taxa without a decelerating trend. Arrivals of neophytes from the Mediterranean region and extra-Mediterranean Europe proceeded at the same speed until ca the 1870s; thereafter the Mediterranean region started to be the main donor of the country’s alien flora. Most species native to more distant areas such as extra-Mediterranean Asia and North America were arriving later. Of the total number of alien taxa, 985 (67.7%) are classified as casual, 408 (28.1%) as naturalized but non-invasive, and 61 (4.2%) as invasive. Alien taxa contribute 33.3% to the total plant diversity ever recorded in the country, or 14.6% to the permanently present flora (excluding extinct natives and including only naturalized alien taxa). These figures arewithin the range reported from other European countries. Currently there are 11 archaeophytes and 50 neophytes with invasive populations in the Czech Republic. Factsheets of the invasive neophytes are provided with information on their invasion history, ecology, habitat affinities and impact, and the map of current distribution. The highest invasive species densities (illustrated by a map) as well as the highest levels of invasion in plant communities are found in cities and villages and their surroundings, floodplains of large rivers, disturbed regions in the north, and agricultural landscapes and forestry plantations in warm lowlands, especially in southern Moravia, and central and eastern Bohemia. The level of invasion in the country decreases with altitude, with neophytes responding to this factor more strongly than archaeophytes. A new quantification of the level of invasion for all phytosociological alliances of the Czech Republic is presented. The habitats and vegetation types harbouring the highest proportions of alien species in the Czech Republic are generally either those with a high level of disturbance or with fluctuating input of resources, especially nutrients, in some cases also water or light. Habitats with limited fluctuation of resource availability such as dry, wet and saline grasslands, baserich fens, and broad-leaved deciduous woodlands appear to be rather resistant to invasion. Future spread of alien species will mainly depend on changing land use and climate.
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alien plants in urban nature reserves from red list species to future invaders
NeoBiota, 2011Co-Authors: V Jarosik, Petr Pysek, Tomas KadlecAbstract:Urban reserves, like other protected areas, aim to preserve species richness but conservation efforts in these protected areas are complicated by high proportions of alien species. We examined which environmental factors determine alien species presence in 48 city reserves of Prague, Czech Republic. We distinguished between archaeophytes, i.e. alien species introduced since the beginning of Neolithic agriculture up to 1500 A. D., and neophytes, i.e. modern invaders introduced after that date, with the former group separately analysed for endangered archaeophytes (listed as C1 and C2 categories on national red list). Archaeophytes responded positively to the presence of arable land that was in place at the time of the reserve establishment, and to a low altitudinal range. In addition to soil properties, neophytes responded to recent human activities with the current proportion of built-up area in reserves serving as a proxy. Endangered archaeophytes, with the same affinity for past arable land as other archaeophytes, were also supported by the presence of current shrubland in the reserve. This suggests that for endangered archaeophytes it may have been difficult to adapt to changing agricultural practices, and shrublands might act as a refugium for them. Forty-six of the 155 neophytes recorded in the reserves are classified as invasive. The reserves thus harbour 67% of the 69 invasive neophytes recorded in the country, and particularly worrisome is that many of the most invasive species are shrubs and trees, a life form that is known to account for widespread invasions with high impacts. Our results thus strongly suggest that in Prague nature reserves there is a high potential for future invasions.
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the distribution of range sizes of native and alien plants in four european countries and the effects of residence time
Diversity and Distributions, 2009Co-Authors: Mark Williamson, Petr Pysek, Stefan Klotz, Katharina Dehnenschmutz, Ingolf Kuhn, M O Hill, Ann Milbau, Jane C StoutAbstract:Aim Do the statistical distributions of range sizes of native and alien species differ? If so, is this because of residence time effects? And can such effects indicate an average time to a maximum? Location Ireland, Britain, Germany and the Czech Republic. Methods The data are presence or absence of higher plants in mapping units of 100 km2 (Ireland and Britain) or c. 130 km2 (Germany and the Czech Republic) in areas varying from 79 to 357 thousand km2. Logit transforms of range sizes so defined were tested for normality, and examined by ANOVA, and by loess, ordinary least square (OLS) and reduced major axis regressions. Results Current range sizes, in logits, are near normally distributed. Those of native plants are larger than those of naturalized neophytes (plants introduced since 1500 ad) and much larger than those of casual neophytes. Archaeophytes (introduced earlier) have range sizes slightly larger than natives, except in Ireland. Residence time, the time since an invasive species arrived in the wild at a certain place, affects range sizes. The relationships of the range of naturalized neophytes to residence time are effectively straight in all four places, showing no significant curvature or asymptote back to 1500, though there are few records between 1500 and 1800. The relationships have an r2 of only about 10%. Both OLS regressions and reduced major axes can be used to estimate the time it takes for the range of a naturalized neophyte to reach a maximum. Main conclusions Established neophytes have smaller range size distributions than natives probably because many have not yet reached their maximum. We estimate it takes at least 150 years, possibly twice that, on average, for the maximum to be reached in areas of the order of 105 km2. Policy needs to allow for the variation in rates of spread and particularly the long time needed to fill ranges. Most naturalized neophytes are still expanding their ranges in Europe.
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distance decay of similarity among european urban floras the impact of anthropogenic activities on β diversity
Global Ecology and Biogeography, 2008Co-Authors: Frank A La Sorte, Petr Pysek, Michael L Mckinney, Stefan Klotz, G L Rapson, Laura Celestigrapow, Ken ThompsonAbstract:Aim We e xamine how two categories of non-native species (archaeophyte and neophyte, introduced before and after 1500, respectively) have had different impacts on β diversity across European urban floras. Our goal is to use the unique biological perspective provided by urban areas, and the contrasting historical and geographical perspectives provided by archaeophytes and neophytes, to infer how non-native species will impact upon β diversity in the future. Location Tw enty-two urban areas located in seven European countries. Methods We used the β -sim dissimilarity index to estimate the level of β diversity for 231 unique pair-wise combinations of 22 urban floras. We examined bivariate plots of dissimilarity by geographical separation of city centres to evaluate distance decay of similarity for native species, archaeophytes and neophytes. Results Based on average percentages, 52.8% (SD = 8.2%) of species in the urban floras were identified as non-native with 28.3% (SD = 6.9%) classified as neophytes and 24.5% (SD = 4.9%) as archaeophytes. Relative to native species, across urban floras, archaeophytes were associated with higher compositional similarity and weaker distance decay patterns, whereas neophytes were associated with lower compositional similarity and stronger distance decay patterns. Main conclusions Across European urban floras, archaeophytes and neophytes occurred in similar numbers but archaeophytes were consistently associated with lower β diversity and neophytes with higher β diversity. Thus, the impact of non-native species on β diversity can be determined, at least in part, through their historical and geographical associations with anthropogenic activities. If archaeophytes represent the long-term biogeographical outcome for human commensal species, neophytes could develop similar patterns. The consequences, however, are likely to be more substantial ecologically and geographically due to the increasing numbers of neophytes and their global anthropogenic associations. Nevertheless, at present, our findings suggest that, based on occurrence information, neophytes have not achieved this state with European urban floras retaining regionally distinct assemblages of neophytes.
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habitat invasions by alien plants a quantitative comparison among mediterranean subcontinental and oceanic regions of europe
Journal of Applied Ecology, 2008Co-Authors: Milan Chytrý, Petr Pysek, Montserrat Vila, L C Maskell, Joan Pino, Xavier Font, S M SmartAbstract:Summary 1. Although invasions by alien plants are major threats to the biodiversity of natural habitats, individual habitats vary considerably in their susceptibility to invasion. Therefore the risk assessment procedures, which are used increasingly by environmental managers to inform effective planning of invasive plant control, require reliable quantitative information on the extent to which different habitats are susceptible to invasion. It is also important to know whether the levels of invasion in different habitats are locally specific or consistent among regions with contrasting climate, flora and history of human impact. 2. We compiled a database of 52 480 vegetation plots from three regions of Europe: Catalonia (Mediterranean‐submediterranean region), Czech Republic (subcontinental) and Great Britain (oceanic). We classified plant species into neophytes, archaeophytes and natives, and calculated the proportion of each group in 33 habitats described by the European Nature Information System (EUNIS) classification. 3. Of 545 alien species found in the plots, only eight occurred in all three regions. Despite this large difference in species composition, patterns of habitat invasions were highly consistent between regions. None or few aliens were found in environmentally extreme and nutrient-poor habitats, e.g. mires, heathlands and high-mountain grasslands. Many aliens were found in frequently disturbed habitats with fluctuating nutrient availability, e.g. in man-made habitats. Neophytes were also often found in coastal, littoral and riverine habitats. 4. Neophytes were found commonly in habitats also occupied by archaeophytes. Thus, the number of archaeophytes can be considered as a good predictor of the neophyte invasion risk. However, neophytes had stronger affinity to wet habitats and disturbed woody vegetation while archaeophytes tended to be more common in dry to mesic open habitats. 5. Synthesis and applications. The considerable inter-regional consistency of the habitat invasion patterns suggests that habitats can be used as a good predictor for the invasion risk assessment. This finding opens promising perspectives for the use of spatially explicit information on habitats, including scenarios of future land-use change, to identify the areas of highest risk of invasion.
Nigel C Bennett - One of the best experts on this subject based on the ideXlab platform.
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a comparison of the ecology of two populations of the common mole rat cryptomys hottentotus hottentotus the effect of aridity on food foraging and body mass
Oecologia, 2000Co-Authors: A C Spinks, Nigel C Bennett, Jennifer U M JarvisAbstract:The aridity food distribution hypothesis (AFDH) maintains that ecological constraints in arid habitats curtail dispersal and promote the evolution of cooperative foraging social groups within the African mole-rats. To evaluate the validity of the AFDH, we investigated inter-habitat differences in food resource characteristics, foraging behaviour, colony size and individual body mass in two common mole-rat populations, one from a mesic and one from an arid habitat. Although food was clumped at both localities, the geophyte density was lower at the arid site. However, Geophytes from the arid site were larger than those from the mesic region, and this is suggested to compensate for the reduced geophyte density, enabling colonies to meet their energy requirements. Differences in food resource characteristics in turn influenced the pattern of foraging, the burrow systems at the arid site being longer and more linear than those from the mesic site. Mean colony size did not differ between the two sites, but animals from the arid site exhibited a reduced individual mass relative to those from the mesic area, probably an adaptation to reduce total colony energy expenditure given the elevated foraging costs in arid environments. The common mole-rat from the arid localities should occur in larger colonies than their mesic counterparts. The results from this investigation do not support this contention.
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foraging in wild and captive colonies of the common mole rat cryptomys hottentotus hottentotus rodentia bathyergidae
Journal of Zoology, 1999Co-Authors: A C Spinks, Nigel C Bennett, Trevor A Branch, Shula Croeser, Jennifer U M JarvisAbstract:The foraging behaviour of wild and captive colonies of the common mole-rat Cryptomys hottentotus hottentotus was investigated. Field studies were undertaken at Steinkopf, an arid site in the Northern Cape, South Africa. The resource biomass and the total available energy here were amongst the highest recorded for any bathyergids, but Geophytes were sparse and widely distributed. The low probability of locating these widely dispersed resources should promote co-operative foraging in these mole-rats. All common geophyte species were consumed, probably because high burrowing costs favour dietary generalism. The mole-rat biomass per metre of burrow system (0.5 ‐1.5 g.m -1 ) remains the lowest of any subterranean mammal. Burrow depths and diameters were positively correlated to the average mass of the mole-rats in each colony, apparently minimizing energetic costs and maximizing foraging success. Bulbs were stored in central food caches, and both field and laboratory data indicated size-based selectivity in their storage and consumption. As predicted by central place foraging theory, large bulbs were preferentially stored, and small bulbs preferentially consumed. However, factors other than energetic considerations may also influence these storage decisions. Total consumption time of bulbs was negatively correlated to animal size, and furthermore smaller bulbs were consumed more rapidly than larger ones. In addition to Geophytestoring, C. h. hottentotus also exhibited an alternative foraging strategy, termed ‘geophyte farming’, in which large bulbs were left and eaten in situ, and served as a renewable resource. Together with these foraging specializations, the evolution of sociality in mole-rats is a key factor which enables them to live in some of the most formidable habitats in Africa.
A. S. Schoeman - One of the best experts on this subject based on the ideXlab platform.
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Foraging in the subterranean social highveld mole-rat ( Cryptomys hottentotus pretoriae ): an investigation into mass-dependent geophyte use and foraging patterns
Journal of Zoology, 2003Co-Authors: G.p. Malherbe, A. S. SchoemanAbstract:The foraging behaviour of captive colonies of the highveld mole-rat Cryptomys hottentotus pretoriae was investigated in an artificial soil-filled burrow system provided with four trays (patches) that varied in geophyte density and mass. An initial trial involving empty trays (only soil) revealed that there was no preference for any specific tray. There were no statistically significant preferences for excavating in any of the patches of different geophyte density. No preferences were evident for excavation in patches containing Geophytes of different mass classes. Empty patches seemed to be preferred over patches containing Geophytes when combinations of geophyte density/mass were investigated. The duration of handling and the rate of consumption of Geophytes were recorded for 23 individuals of two mass classes. Handling time of Geophytes was not related to mole-rat sex, but was strongly linked to mole-rat mass class. Handling time of Geophytes was related to geophyte mass class. Small Geophytes were less profitable to consume. These findings are considered in light of optimal foraging theory and the situation in the field. It was concluded that the mole-rats generally followed the qualitative predictions of optimal foraging theory, although falling short of being energy maximizers.