Ehnes, Roswitha (2014)
Allometry – Relations to Energy and Abundance.
Technische Universität Darmstadt
Dissertation, Erstveröffentlichung

Kurzbeschreibung (Abstract)

During my PhD, I focused on metabolic rates of litter- and soil-dwelling invertebrates, parameters that exert influence on them or are influenced by metabolism. I started with consumption experi- ments, comparing the estimated amounts of energy taken up with the energetic demand estimated via metabolic-rate measurements. These experiments showed that, generally, ingestion as well as metabolic rates increase for beetle and spider species with increasing temperature. However, while ingestion increased only slightly with increasing temperature, metabolic demand increased strongly thus reducing the ingestion efficiency with increasing temperature (Chapter 3). This might have strong effects on the whole food web in a natural system. Populations might depict a higher stability but on the other hand, due to the lowered ingestion efficiencies, predators might become more prone to starvation and even extinction (Chapter 3). In the next study again metabolic rates and consumption rates (functional responses) were compared across a temperature range, but with a different focus. Here, ground beetles in combination with a more resident and a mobile prey type were used to examine the different effects of temperature on these predator-prey pairs (Chapter 4). Generally, increasing temperature led to an increase in metabolic rate, a decrease in energetic ef- ficiency and a decrease in handling time. However, the effect of increased temperature on attack rate differed for the two prey types. For mobile prey the attack rate increased with temperature, while it was not affected for the more resident prey. This implies that an increase in temperature might stabilize population dynamics. Since the first two studies had shown that the metabolic rate of different organisms is differently affected by body mass and temperature, I focused on the ef- fects of body mass and temperature on metabolic rates for my next study. Therefore, I compiled a large dataset on metabolic rates of mainly soil-dwelling invertebrates by performing measurements of respiration and by literature research (Chapter 5). With this dataset I tested a very prominent theory (Metabolic Theory of Ecology) on how metabolism depends on body mass and temperature. As this theory uses a fixed three-quarter allometric exponent (fixed body-mass dependence), which the results of chapter 3 and 4 proved not to be useful, I also used a relaxed version (unrestricted body-mass and temperature dependence). Finally, I tested a model, similar to the relaxed one but incorporating phylogenetic information, thus each phylogenetic group would be fit independently. This phylogenetic model obtained the highest quality thus emphasizing the importance of account- ing for the phylogenetic affiliation of an organism (Chapter 5). Thus, the results of this study allow a conservative energy-demand estimation for different terrestrial invertebrate species. Having seen that metabolic rates of organisms as well as their consumption rates increase with temperature, the question remains how the assimilation efficiencies change. The effect of tempera- ture on the assimilation efficiencies of different consumer types (carnivore, detritivore, herbivore) had not been studied yet. For filling this gap, a database on assimilation efficiencies for different consumer types was used and the database on metabolic rates (Chapter 5). Metabolic rates in- creased with temperature for all consumer types while the assimilation efficiency only increased for herbivores and was independent of temperature for the other two consumer types (Chapter 6). From this it follows that maintenance consumption rates increase with temperature, however the amount of increase differs between the consumer types. For carnivores the metabolic rates in- creased stronger with increasing temperature than did their consumption rates, which might lead to starvation. Accelerated consumption rates of detritivores could lead to increased turnover rates and might result in increasing biomass of the populations (Chapter 6). Aside from using the metabolic-rate data with other laboratory data, it may also provide informa- tion on the energy distribution in natural systems while its direct measurement is not possible. For testing the Structured Resource Theory of Sexual Reproduction (SRTS) abundance and body-mass data on oribatid mites in differently used habitats were used to estimate the metabolic demand of the oribatid community (Chapter 7). The SRTS suggests that limited resources favor sexually re- producing consumers while ample resources would be superiorly exploited by parthenogenetically reproducing species. Abundance and metabolic demand served as a surrogate for resource supply. The data supported the predictions of the SRTS as in habitats with a high amount of resources (as indicated by high population densities or high metabolic rates) parthenogenetic reproduction occurred in a higher proportion (Chapter 7). Finally, I used the metabolic parameters to estimate the energetic demand of soil-invertebrate communities in differently used forests. Abundances and body masses (via body lengths) were obtained by field sampling. Based on these data I calculated the metabolic demand, the population energy use (PEU) and the biomass of the different species present (Chapter 8). Thus, this dataset allowed testing different patterns that have been described to apply to energy or biomass distribution in a community. The energetic equivalence is observed if populations of small and large organisms use the same amount of energy. The biomass equivalence on the other hand states that the biomasses are independent of body mass. I compared the results with these patterns. Generally, metabolic rates increased with body mass of the species and abun- dances declined independently of phylogenetic group, land-use type or feeding type. Biomasses increased in all cases thus clearly rejecting the biomass-equivalence hypothesis. Population en- ergy use mostly increased with body mass. Furthermore, a more detailed analysis (phylogenetic groups separately in each land-use type) showed that the energetic equivalence is sometimes met and sometimes not. However, the data support predictions of the resource-thinning hypothesis, which states that abundances should decrease with trophic level, and mostly the allometric-degree hypothesis stating that PEU should increase with increasing body mass. Thus, predictions from food-web theory regarding the structure of natural communities are met and further integration of metabolic and food-web theory might help to explain the natural community structures.

Frage zum Eintrag

Redaktionelle Details anzeigen