J Ganzhorn - Academia.edu (original) (raw)

Papers by J Ganzhorn

Die Naturwissenschaften, 2011

Madagascar provides some of the rare examples where two or more primate species of the same genus... more Madagascar provides some of the rare examples where two or more primate species of the same genus and with seemingly identical niche requirements occur in sympatry. If congeneric primate species co-occur in other parts of the world, they differ in size in a way that is consistent with Hutchinson's rule for coexisting species, or they occupy different ecological niches. In some areas of Madagascar, mouse lemurs do not follow these "rules" and thus seem to violate one of the principles of community ecology. In order to understand the mechanisms that allow coexistence of sympatric congeneric species without obvious niche differentiation, we studied food composition of two identical sized omnivorous mouse lemur species, Microcebus griseorufus and M. murinus with the help of stable isotope analyses (δ(15)N and δ(13)C). The two species are closely related sister species. During the rich season, when food seems abundant, the two species do not differ in their nitrogen isotop...

Behavioral Ecology and Sociobiology, 2000

Cheirogaleids are one of the most primitive extant primate taxa in the world. Their lifestyle and... more Cheirogaleids are one of the most primitive extant primate taxa in the world. Their lifestyle and mating system, therefore, have been considered to be representative for social systems in primate ancestors. Accepted models of social evolution in primates state that pair-bonding has evolved secondarily from diurnal group-living taxa and should therefore be constrained primarily to diurnal species. In contrast to these assumptions, the nocturnal fat-tailed dwarf lemur (Cheirogaleus medius) lives in permanent pairs, with obligate paternal care probably representing the evolutionary basis of pairliving. In this sociobiological field study, we analyzed the reproduction strategy of C. medius in the tropical forest of western Madagascar. In the rainy seasons from 1995 to 1999, 173 individuals of C. medius were captured and individually marked and 131 were genetically characterized through seven microsatellite loci. Additionally, 36 of these individuals were radio-tracked and observed. For 53 genotyped individuals, including 16 offspring, information about pair-bonding and family structure was known from field observations. Genetic analyses revealed that yearlings and infants living with an adult pair were in all cases sibs of the social mother. However, C. medius does not restrain from extra-pair copulations (EPCs) and a high rate of extra-pair paternity (44%) was detected. Males sired offspring with their female partners as well as with extra-pair females within the same year, indicating that males may increase their reproductive success by EPCs without necessarily running the risk of cuckoldry. Females on the other hand do not seem to run the risk of reduced paternal care, either because males cannot detect relatedness of young, or because they might even increase their inclusive fitness by raising offspring of closely related males. Since females reproduce preferentially with territory holders and no paternity could be assigned to floating males, superior genetic quality of the males might be crucial for female choice.

Ecology and evolution, Apr 2, 2016

Dietary characteristics and environmental variables are important selective factors directing eco... more Dietary characteristics and environmental variables are important selective factors directing ecological diversification in rodents. On Madagascar, the introductions and spread of the commensal black rat (Rattus rattus) can be seen as example cases to study dietary niche occupation and dietary adaptation in an insular environment. We investigate how tooth wear as a measure of dietary adaptation of black rats differs between four distinct habitats (village, manioc fields, spiny forest, and rainforest) with different dietary resources. We use the 3D surface texture analysis (3DST, using 30 parameters according to ISO 25178) as a measure of dietary abrasiveness. 3DST is applied on the occlusal surface of the upper first molar of 37 black rat specimens. The rainforest sample displays less rough and less voluminous surface textures compared to the village samples as indicated by smaller values for height parameters (Sa, Sp, Sq), inverse areal material ratio (Smc), and volume parameters (...

Primate Conservation, 2009

Primates, 1985

Two groups of Avahi laniger were studied in the For6t de Analamozoatra near Perinet in the easter... more Two groups of Avahi laniger were studied in the For6t de Analamozoatra near Perinet in the eastern rainforest of Madagascar from August to October 1984. Overlap between the home ranges of neighbouring groups of A. laniger was minimal. Group size ranged from one to four individuals with a median group size of two. In four out often groups a baby was born between August and September. A. laniger were most active after dusk and before dawn. They had an extended resting period around midnight. Their diet consisted mostly of leaves from at least 17 different plant species. They also ate flowers. Fruit eating was recorded twice. Leaves eaten had high contents of protein and sugar but did not contain alkaloids. The concentration of condensed tannins did not differ between food items and non-food items. There was no indication of competition with other prosimians that might explain their nocturnality.

PLoS ONE, 2009

Background: The ecological factors contributing to the evolution of tropical vertebrate communiti... more Background: The ecological factors contributing to the evolution of tropical vertebrate communities are still poorly understood. Primate communities of the tropical Americas have fewer folivorous but more frugivorous genera than tropical regions of the Old World and especially many more frugivorous genera than Madagascar. Reasons for this phenomenon are largely unexplored. We developed the hypothesis that Neotropical fruits have higher protein concentrations than fruits from Madagascar and that the higher representation of frugivorous genera in the Neotropics is linked to high protein concentrations in fruits. Low fruit protein concentrations in Madagascar would restrict the evolution of frugivores in Malagasy communities. Methodology/Principal Findings: We reviewed the literature for nitrogen concentrations in fruits from the Neotropics and from Madagascar, and analyzed fruits from an additional six sites in the Neotropics and six sites in Madagascar. Fruits from the Neotropical sites contain significantly more nitrogen than fruits from the Madagascar sites. Nitrogen concentrations in New World fruits are above the concentrations to satisfy nitrogen requirements of primates, while they are at the lower end or below the concentrations to cover primate protein needs in Madagascar. Conclusions/Significance: Fruits at most sites in the Neotropics contain enough protein to satisfy the protein needs of primates. Thus, selection pressure to develop new adaptations for foods that are difficult to digest (such as leaves) may have been lower in the Neotropics than in Madagascar. The low nitrogen concentrations in fruits from Madagascar may contribute to the almost complete absence of frugivorous primate species on this island.

Conservation Genetics, 2004

Habitat fragmentation inhibits gene flow between populations often resulting in a loss of genetic... more Habitat fragmentation inhibits gene flow between populations often resulting in a loss of genetic diversity with possible negative effects on fitness parameters. In vertebrates, growing evidence suggests that such genetic diversity is particularly important at the level of the major histocompatibility complex (MHC) because its gene products play an important role in immune functions. Diversity in the MHC is assumed to improve population viability. Here, we investigated the impact of forest fragmentation on the genetic variability of one of the functionally important parts of the MHC, DRB exon 2, of the endemic mouse lemur Microcebus murinus by comparing populations inhabiting two littoral forest fragments of different size in southeastern Madagascar. Twelve different alleles of DRB exon 2 were found in 145 individuals of M. murinus with high levels of sequence divergence between alleles. In both subpopulations, levels of genetic diversity were high, and the genetic analyses revealed only limited effects of fragmentation. Significantly more non-synonymous than synonymous substitutions were found in the functionally important antigen recognition and binding sites indicating selection processes maintaining MHC polymorphism. This is the first study on MHC variation in a free-ranging Malagasy lemur population.

Naturwissenschaften, 1993

Goodman, Steven M., Rasoloarison, Rodin M., Ganzhorn, Jörg U. (2004): On the specific identificat... more Goodman, Steven M., Rasoloarison, Rodin M., Ganzhorn, Jörg U. (2004): On the specific identification of subfossil Cryptoprocta (Mammalia, Carnivora) from Madagascar. Zoosystema 26 (1): 129-143

International Forestry Review, 2015

Journal of Comparative …, 2003

International Journal of Primatology - INT J PRIMATOL, 1998

The goal of this study was to identify causes for lower population densities of mouse lemurs (Mic... more The goal of this study was to identify causes for lower population densities of mouse lemurs (Microcebus murinus) in secondary than in primary dry deciduous forests of western Madagascar. Variations in the abundance of Microcebus murinus are linked to the capacity to enter energy-saving torpor during the dry season. Under natural conditions in primary forest, Microcebus murinus can maintain daily torpor (and possibly hibernation) as long as body temperatures remain below 28°C. Females are more likely to hibernate than males, resulting in skewed sex ratios of captured Microcebus murinus in the primary forest. In the secondary forest the sex ratio of subjects captured during the dry season is more balanced than in primary forest, indicating that fewer females go into torpor in secondary than in primary forest. Secondary forests have fewer large standing or fallen trees that might provide holes as shelter for Microcebus murinus. Ambient temperatures are higher in secondary than in prim...

Oryx, 2001

Madagascar is renowned not only for its high biodiversity and high degree of endemism, but also f... more Madagascar is renowned not only for its high biodiversity and high degree of endemism, but also for ongoing loss of the original primary vegetation. Here we draw attention to the critical degree of vulnerability of Madagascar's littoral forest, western dry deciduous forest, and evergreen forests of the high plateau. Conservation efforts in these forest formations have been low compared to those in the evergreen rainforest of eastern Madagascar. Due to their fragmented nature these ecosystems urgently require reinforced conservation programmes.

Oikos, 2014

ABSTRACT A central goal of nutritional ecology is to understand how variation in food quality lim... more ABSTRACT A central goal of nutritional ecology is to understand how variation in food quality limits the persistence of wild animal populations. Habitat suitability for browsing mammals is strongly affected by concentrations of nutrients and plant secondary metabolites (PSMs), but our understanding of this is based mostly on short-term experiments of diet selection involving captive animals. In the wild, browsers forage in biologically, chemically and spatially-complex environments, and foraging decisions in response to varying food quality will be correspondingly complicated. We have identified four steps that must be achieved in order to translate our understanding from laboratory experiments to populations of mammalian browsers: 1) knowing what foods and how much of these wild browsers eat, as well as what they avoid eating; 2) knowing the relevant aspects of plant nutritional and defensive chemistry to measure in a given system and how to measure them; 3) understanding the spatial distribution of nutrients and PSMs in plant communities, the costs they impose on foraging and the effects on animals’ distributions; and 4) having appropriate statistical tools to analyse the data. We discuss prospects for each of these prerequisites for extending laboratory studies of nutritional quality, and review recent developments that may offer solutions for field studies. We also provide a synthesis of how to use this nutritional knowledge to link food quality to population regulation in wild mammals and describe examples that have successfully achieved this aim.