Browsing by Subject "BODY-SIZE"

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  • Radchuk, Viktoriia; Reed, Thomas; Teplitsky, Celine; van de Pol, Martijn; Charmantier, Anne; Hassall, Christopher; Adamik, Peter; Adriaensen, Frank; Ahola, Markus P.; Arcese, Peter; Miguel Aviles, Jesus; Balbontin, Javier; Berg, Karl S.; Borras, Antoni; Burthe, Sarah; Clobert, Jean; Dehnhard, Nina; de Lope, Florentino; Dhondt, Andre A.; Dingemanse, Niels J.; Doi, Hideyuki; Eeva, Tapio; Fickel, Joerns; Filella, Iolanda; Fossoy, Frode; Goodenough, Anne E.; Hall, Stephen J. G.; Hansson, Bengt; Harris, Michael; Hasselquist, Dennis; Hickler, Thomas; Joshi, Jasmin; Kharouba, Heather; Gabriel Martinez, Juan; Mihoub, Jean-Baptiste; Mills, James A.; Molina-Morales, Mercedes; Moksnes, Arne; Ozgul, Arpat; Parejo, Deseada; Pilard, Philippe; Poisbleau, Maud; Rousset, Francois; Roedel, Mark-Oliver; Scott, David; Carlos Senar, Juan; Stefanescu, Constanti; Stokke, Bard G.; Kusano, Tamotsu; Tarka, Maja; Tarwater, Corey E.; Thonicke, Kirsten; Thorley, Jack; Wilting, Andreas; Tryjanowski, Piotr; Merilä, Juha; Sheldon, Ben C.; Moller, Anders Pape; Matthysen, Erik; Janzen, Fredric; Dobson, F. Stephen; Visser, Marcel E.; Beissinger, Steven R.; Courtiol, Alexandre; Kramer-Schadt, Stephanie (2019)
    Biological responses to climate change have been widely documented across taxa and regions, but it remains unclear whether species are maintaining a good match between phenotype and environment, i.e. whether observed trait changes are adaptive. Here we reviewed 10,090 abstracts and extracted data from 71 studies reported in 58 relevant publications, to assess quantitatively whether phenotypic trait changes associated with climate change are adaptive in animals. A meta-analysis focussing on birds, the taxon best represented in our dataset, suggests that global warming has not systematically affected morphological traits, but has advanced phenological traits. We demonstrate that these advances are adaptive for some species, but imperfect as evidenced by the observed consistent selection for earlier timing. Application of a theoretical model indicates that the evolutionary load imposed by incomplete adaptive responses to ongoing climate change may already be threatening the persistence of species.
  • Zliobaite, Indre; Fortelius, Mikael (2020)
    The Red Queen's hypothesis portrays evolution as a never-ending competition for expansive energy, where one species' gain is another species' loss. The Red Queen is neutral with respect to body size, implying that neither small nor large species have a universal competitive advantage. Here we ask whether, and if so how, the Red Queen's hypothesis really can accommodate differences in body size. The maximum population growth in ecology clearly depends on body size-the smaller the species, the shorter the generation length, and the faster it can expand given sufficient opportunity. On the other hand, large species are more efficient in energy use due to metabolic scaling and can maintain more biomass with the same energy. The advantage of shorter generation makes a wide range of body sizes competitive, yet large species do not take over. We analytically show that individuals consume energy and reproduce in physiological time, but need to compete for energy in real time. The Red Queen, through adaptive evolution of populations, balances the pressures of real and physiological time. Modeling competition for energy as a proportional prize contest from economics, we further show that Red Queen's zero-sum game can generate unimodal hat-like patterns of species rise and decline that can be neutral in relation to body size.
  • Jelenkovic, Aline; Rebato, Esther (2016)
    Background: Earlier menarche has been related to shorter height and greater obesity-related anthropometric dimensions and blood pressure in women. Boys and girls with earlier maternal menarcheal age (MMA) have shown greater height and body mass index (BMI) in childhood. Aim: To analyse associations of menarcheal age with their own and their children's anthropometric dimensions and blood pressure. Subjects and methods: The sample consisted of 493 women and their children (aged 2-19 years) from Greater Bilbao (Basque Country, Spain). For both generations there is information on 19 anthropometric dimensions, blood pressure and socio-demographic characteristics. Linear regressions adjusted for different covariates were used to analyse the associations. Results: Menarcheal age in women showed the greatest positive associations with iliospinal height and ectomorphy and negative associations with BMI, sum of six skin-folds, endomorphy and mesomorphy. Boys with earlier MMA had greater body heights and breadths, particularly iliospinal height and biacromial breadth (0.10z-score/year; p Conclusion: Children with earlier MMA tend to have greater anthropometric dimensions. Adolescent growth spurt might affect these relationships, at least in girls.
  • Rolls, Robert J.; Hayden, Brian; Kahilainen, Kimmo K. (2017)
    Climate change and species invasions represent key threats to global biodiversity. Subarctic freshwaters are sentinels for understanding both stressors because the effects of climate change are disproportionately strong at high latitudes and invasion of temperate species is prevalent. Here, we summarize the environmental effects of climate change and illustrate the ecological responses of freshwater fishes to these effects, spanning individual, population, community and ecosystem levels. Climate change is modifying hydrological cycles across atmospheric, terrestrial and aquatic components of subarctic ecosystems, causing increases in ambient water temperature and nutrient availability. These changes affect the individual behavior, habitat use, growth and metabolism, alter population spawning and recruitment dynamics, leading to changes in species abundance and distribution, modify food web structure, trophic interactions and energy flow within communities and change the sources, quantity and quality of energy and nutrients in ecosystems. Increases in temperature and its variability in aquatic environments underpin many ecological responses; however, altered hydrological regimes, increasing nutrient inputs and shortened ice cover are also important drivers of climate change effects and likely contribute to context-dependent responses. Species invasions are a complex aspect of the ecology of climate change because the phenomena of invasion are both an effect and a driver of the ecological consequences of climate change. Using subarctic freshwaters as an example, we illustrate how climate change can alter three distinct aspects of species invasions: (1) the vulnerability of ecosystems to be invaded, (2) the potential for species to spread and invade new habitats, and (3) the subsequent ecological effects of invaders. We identify three fundamental knowledge gaps focused on the need to determine (1) how environmental and landscape characteristics influence the ecological impact of climate change, (2) the separate and combined effects of climate and non-native invading species and (3) the underlying ecological processes or mechanisms responsible for changes in patterns of biodiversity.
  • Allegaert, Karel; Olkkola, Klaus T.; Owens, Katie H.; Van de Velde, Marc; de Maat, Monique M.; Anderson, Brian J.; PACIA Study Grp (2014)
  • Parravicini, Valeriano; Casey, Jordan M.; Schiettekatte, Nina M. D.; Brandl, Simon J.; Pozas-Schacre, Chloe; Carlot, Jeremy; Edgar, Graham J.; Graham, Nicholas A. J.; Harmelin-Vivien, Mireille; Kulbicki, Michel; Strona, Giovanni; Stuart-Smith, Rick D. (2020)
    Understanding species' roles in food webs requires an accurate assessment of their trophic niche. However, it is challenging to delineate potential trophic interactions across an ecosystem, and a paucity of empirical information often leads to inconsistent definitions of trophic guilds based on expert opinion, especially when applied to hyperdiverse ecosystems. Using coral reef fishes as a model group, we show that experts disagree on the assignment of broad trophic guilds for more than 20% of species, which hampers comparability across studies. Here, we propose a quantitative, unbiased, and reproducible approach to define trophic guilds and apply recent advances in machine learning to predict probabilities of pairwise trophic interactions with high accuracy. We synthesize data from community-wide gut content analyses of tropical coral reef fishes worldwide, resulting in diet information from 13,961 individuals belonging to 615 reef fish. We then use network analysis to identify 8 trophic guilds and Bayesian phylogenetic modeling to show that trophic guilds can be predicted based on phylogeny and maximum body size. Finally, we use machine learning to test whether pairwise trophic interactions can be predicted with accuracy. Our models achieved a misclassification error of less than 5%, indicating that our approach results in a quantitative and reproducible trophic categorization scheme, as well as high-resolution probabilities of trophic interactions. By applying our framework to the most diverse vertebrate consumer group, we show that it can be applied to other organismal groups to advance reproducibility in trait-based ecology. Our work thus provides a viable approach to account for the complexity of predator-prey interactions in highly diverse ecosystems.
  • Maria Ariza, Gloria; Jacome, Jorge; Eduardo Esquivel, Hector; Kotze, Johan D. (2021)
    Little is known about the successional dynamics of insects in the highly threatened tropical dry forest (TDF) ecosystem. For the first time, we studied the response of carabid beetles to vegetal succession and seasonality in this ecosystem in Colombia. Carabid beetles were collected from three TDF habitat types in two regions in Colombia: initial successional state (pasture), early succession, and intermediate succession (forest). The surveys were performed monthly for 13 months in one of the regions (Armero) and during two months, one in the dry and one in the wet season, in the other region (Cambao). A set of environmen-tal variables were recorded per month at each site. Twenty-four carabid beetle species were collected during the study. Calosoma alternans and Megacephala affinis were the most abundant species, while most species were of low abundance. Forest and pasture beetle assemblages were distinct, while the early succession assemblage overlapped with these assemblages. Canopy cover, litter depth, and soil and air temperatures were important in structuring the assemblages. Even though seasonality did not affect the carabid beetle assemblage, individual species responded positively to the wet season. It is shown that early successional areas in TDF could potentially act as habitat corridors for species to recolonize forest areas, since these successional areas host a number of species that inhabit forests and pastures. Climatic variation, like the El Nino episode during this study, appears to affect the carabid beetle assemblage negatively, exasperating concerns of this already threatened tropical ecosystem.
  • Mück, Isabel; Heubel, Katja U. (2018)
    Although it has become clear that sexual selection may shape mating systems and drive speciation, the potential constraints of environmental factors on processes and outcomes of sexual selection are largely unexplored. Here, we investigate the geographic variation of such environmental factors, more precisely the quality and quantity of nest resources (bivalve shells) along a salinity gradient in the Baltic Sea Area (Baltic Sea, Sounds and Belts, and Kattegat). We further test whether we find any salinity-associated morphological differences in body size between populations of common gobies Pomatoschistus microps, a small marine fish with a resource-based mating system. In a geographically expansive field study, we sampled 5 populations of P. microps occurring along the salinity gradient (decreasing from West to East) in the Baltic Sea Area over 3 consecutive years. Nest resource quantity and quality decreased from West to East, and a correlation between mussel size and male body size was detected. Population density, sex ratios, mating- and reproductive success as well as brood characteristics also differed between populations but with a less clear relation to salinity. With this field study we shed light on geographic variation of distinct environmental parameters possibly acting on population differentiation. We provide insights on relevant ecological variation, and draw attention to its importance in the framework of context-dependent plasticity of sexual selection.
  • Silventoinen, Karri; Jelenkovic, Aline; Latvala, Antti; Sund, Reijo; Yokoyama, Yoshie; Ullemar, Vilhelmina; Almqvist, Catarina; Derom, Catherine A.; Vlietinck, Robert F.; Loos, Ruth J. F.; Kandler, Christian; Honda, Chika; Inui, Fujio; Iwatani, Yoshinori; Watanabe, Mikio; Rebato, Esther; Stazi, Maria A.; Fagnani, Corrado; Brescianini, Sonia; Hur, Yoon-Mi; Jeong, Hoe-Uk; Cutler, Tessa L.; Hopper, John L.; Busjahn, Andreas; Saudino, Kimberly J.; Ji, Fuling; Ning, Feng; Pang, Zengchang; Rose, Richard J.; Koskenvuo, Markku; Heikkilä, Kauko; Cozen, Wendy; Hwang, Amie E.; Mack, Thomas M.; Siribaddana, Sisira H.; Hotopf, Matthew; Sumathipala, Athula; Rijsdijk, Fruhling; Sung, Joohon; Kim, Jina; Lee, Jooyeon; Lee, Sooji; Nelson, Tracy L.; Whitfield, Keith E.; Tan, Qihua; Zhang, Dongfeng; Llewellyn, Clare H.; Fisher, Abigail; Burt, S. Alexandra; Klump, Kelly L.; Knafo-Noam, Ariel; Mankuta, David; Abramson, Lior; Medland, Sarah E.; Martin, Nicholas G.; Montgomery, Grant W.; Magnusson, Patrik K. E.; Pedersen, Nancy L.; Aslan, Anna K. Dahl; Corley, Robin P.; Huibregtse, Brooke M.; OEncel, Sevgi Y.; Aliev, Fazil; Krueger, Robert F.; Mcgue, Matt; Pahlen, Shandell; Willemsen, Gonneke; Bartels, Meike; Van Beijsterveldt, Catharina E. M.; Silberg, Judy L.; Eaves, Lindon J.; Maes, Hermine H.; Harris, Jennifer R.; Brandt, Ingunn; Nilsen, Thomas S.; Rasmussen, Finn; Tynelius, Per; Baker, Laura A.; Tuvblad, Catherine; Ordonana, Juan R.; Sanchez-Romera, Juan F.; Colodro-Conde, Lucia; Gatz, Margaret; Butler, David A.; Lichtenstein, Paul; Goldberg, Jack H.; Harden, K. Paige; Tucker-Drob, Elliot M.; Duncan, Glen E.; Buchwald, Dedra; Tarnoki, Adam D.; Tarnoki, David L.; Franz, Carol E.; Kremen, William S.; Lyons, Michael J.; Maia, Jose A.; Freitas, Duarte L.; Turkheimer, Eric; Sorensen, Thorkild I. A.; Boomsma, Dorret I.; Kaprio, Jaakko (2017)
    Whether monozygotic (MZ) and dizygotic (DZ) twins differ from each other in a variety of phenotypes is important for genetic twin modeling and for inferences made from twin studies in general. We analyzed whether there were differences in individual, maternal and paternal education between MZ and DZ twins in a large pooled dataset. Information was gathered on individual education for 218,362 adult twins from 27 twin cohorts (53% females; 39% MZ twins), and on maternal and paternal education for 147,315 and 143,056 twins respectively, from 28 twin cohorts (52% females; 38% MZ twins). Together, we had information on individual or parental education from 42 twin cohorts representing 19 countries. The original education classifications were transformed to education years and analyzed using linear regression models. Overall, MZ males had 0.26 (95% CI [0.21, 0.31]) years and MZ females 0.17 (95% CI [0.12, 0.21]) years longer education than DZ twins. The zygosity difference became smaller in more recent birth cohorts for both males and females. Parental education was somewhat longer for fathers of DZ twins in cohorts born in 1990-1999 (0.16 years, 95% CI [0.08, 0.25]) and 2000 or later (0.11 years, 95% CI [0.00, 0.22]), compared with fathers of MZ twins. The results show that the years of both individual and parental education are largely similar in MZ and DZ twins. We suggest that the socio-economic differences between MZ and DZ twins are so small that inferences based upon genetic modeling of twin data are not affected.
  • Korponai, Janos; Köver, Csilla; Lopez-Blanco, Charo; Gyulai, Istvan; Forro, Laszlo; Katalinic, Ana; Ketola, Mirva; Nevalainen, Liisa; Luoto, Tomi P.; Sarmaja-Korjonen, Kaarina Margareta; Magyari, Enikö; Weckström, Jan; Urak, Istvan; Vadkerti, Edit; Buczko, Krisztina (2020)
    The body size of aquatic invertebrates is, to a great extent, dependent on ambient temperature, but size distributions are also determined by other factors like food supply and predation. The effect of temperature on organisms is formulated in the temperature-size hypothesis, which predicts a smaller body size with increasing temperature. In this study, the effect of temperature on the subfossil remains of three littoral Cladocera (Alona affnis, A. quadrangularis, and Chydorus cf. sphaericus) was investigated. Exoskeletal remains of these species can be found in large numbers in lacustrine sediments and over a wide north-south range in Europe. The total length of both headshield and postabdomen for A. affinis and A. quadrangularis and carapace length for C. cf. sphaericus were measured to observe their response to changes in latitude and temperature. A different response to ambient temperature in the growth of body parts was observed. The size of the headshields of both Alona species and of the carapace of Chydorus was significantly larger in colder regions as opposed to warm ones. It turned out that the postabdomen was not a good predictor of ambient temperature. While the sizes of all remains increased with latitude, the sizes of the Alona remains was smaller in the mountain lakes of the Southern Carpathians than in other cold lakes, in this case in Finland, a fact indicative of the importance of other factors on size distribution. This study demonstrates that a morphological response to climate is present in littoral cladocerans, and, therefore, changes in the length of headshield and carapace may be used as a proxy for climate changes in paleolimnological records.
  • Lehtonen, Topi K.; Wong, Bob B. M.; Kvarnemo, Charlotta (2016)
    Background: Parental allocation and reproductive success are often strongly influenced by environmental factors. In this respect, salinity is a key factor influencing species distributions and community structure in aquatic animals. Nevertheless, the effects of salinity on reproductive behaviours are not well known. Here, we used the sand goby (Pomatoschistus minutus), a small fish inhabiting a range of different salinities, to experimentally assess the effects of changes in salinity on nesting behaviour, a key component of reproduction in sand gobies and many other taxa. Results: We found that salinity levels influenced some aspects of male nesting behaviour (i.e. nest entrance size) but not others (i.e. latency to build a nest, choice of nest site, sand on top of nest) and that small and large individuals were differently affected. In particular, the importance of body size in adjustment of nest entrance depended on the salinity level. Conclusion: The results support the prediction that geographically widespread aquatic species, such as sand gobies, are able to perform well under a range of salinity levels. The phenotype by environment interaction found between male size and behavioural responses to salinity can, in turn, help to explain the notable variation observed in nest-building (and other) behaviours closely linked to reproduction.
  • Peng, Li Qing; Tang, Min; Liao, Jia Hong; Liang, Shi Yuan; Gan, Li Tao; Hua, Ke Jun; Chen, Yan; Li, Hong; Chen, Wei; Merilä, Juha (2020)
    Organisms living in extreme environments, such as amphibians inhabiting the Tibetan plateau, are faced with a magnitude of potentially strong selection pressures. With an average elevation exceeding 4500 m, the Tibetan plateau is mainly characterized by low temperatures, but little is known about the influence of this factor on the growth, development, and behaviour of amphibian larvae living in this environment. Using a common garden experiment, we studied the influence of temperatures on the early growth and development of tadpoles of the Tibetan brown frog (Rana kukunoris) endemic to the eastern Tibetan plateau. We discovered that temperature had a significant influence on early growth and development of the tadpoles, with those undergoing high-temperature treatment growing and developing faster than their siblings from a low-temperature treatment. However, high-altitude individuals grew faster than low-altitude individuals at low temperatures. while the opposite was true at high temperatures. These results support the temperature adaptation hypothesis, as tadpoles' growth and developmental rates were maximized at the temperatures experienced in their native environments. These results suggest that variation in ambient temperature. combined with evolutionary adaptation to temperature of local environments, is probably one of the most critical environmental factors shaping altitudinal differences in the growth and development of amphibian larvae on the Tibetan plateau.
  • Toli, Elisavet A.; Noreikiene, Kristina; De Faveri, Jacquelin; Merila, Juha (2017)
    Evidence for phenotypic plasticity in brain size and the size of different brain parts is widespread, but experimental investigations into this effect remain scarce and are usually conducted using individuals from a single population. As the costs and benefits of plasticity may differ among populations, the extent of brain plasticity may also differ from one population to another. In a common garden experiment conducted with three-spined sticklebacks (Gasterosteus aculeatus) originating from four different populations, we investigated whether environmental enrichment (aquaria provided with structural complexity) caused an increase in the brain size or size of different brain parts compared to controls (bare aquaria). We found no evidence for a positive effect of environmental enrichment on brain size or size of different brain parts in either of the sexes in any of the populations. However, in all populations, males had larger brains than females, and the degree of sexual size dimorphism (SSD) in relative brain size ranged from 5.1 to 11.6% across the populations. Evidence was also found for genetically based differences in relative brain size among populations, as well as for plasticity in the size of different brain parts, as evidenced by consistent size differences among replicate blocks that differed in their temperature.
  • Gonda, Maria Abigel; Herczeg, Gabor; Merilä, Juha (2013)
  • O'Sullivan, Ronan James; Aykanat, Tutku; Johnston, Susan E.; Kane, Adam; Poole, Russell; Rogan, Ger; Prodöhl, Paulo A.; Primmer, Craig R.; McGinnity, Philip; Reed, Thomas Eric (2019)
    Comparing observed versus theoretically expected evolutionary responses is important for our understanding of the evolutionary process, and for assessing how species may cope with anthropogenic change. Here, we document directional selection for larger female size in Atlantic salmon, using pedigree-derived estimates of lifetime reproductive success as a fitness measure. We show the trait is heritable and, thus, capable of responding to selection. The Breeder's Equation, which predicts microevolution as the product of phenotypic selection and heritability, predicted evolution of larger size. This was at odds, however, with the observed lack of either phenotypic or genetic temporal trends in body size, a so-called "paradox of stasis." To investigate this paradox, we estimated the additive genetic covariance between trait and fitness, which provides a prediction of evolutionary change according to Robertson's secondary theorem of selection (STS) that is unbiased by missing variables. The STS prediction was consistent with the observed stasis. Decomposition of phenotypic selection gradients into genetic and environmental components revealed a potential upward bias, implying unmeasured factors that covary with trait and fitness. These results showcase the power of pedigreed, wild population studies-which have largely been limited to birds and mammals-to study evolutionary processes on contemporary timescales.
  • Wolf, Jana I.; Punttila, Pekka; Seppä, Perttu (2018)
    1. Size polymorphism is often connected to alternative life-history traits, which may eventually lead to distinct size classes. In the ant Myrmica ruginodis, larger macrogyne and smaller microgyne queen morphs have been suggested to follow different reproductive strategies, which has presumably resulted in several differences in their key life-history traits. 2. In this study, we examine the association of queen-size morphs with colony queen number (monogyny vs. polygyny), dispersal and queen recruitment patterns, as well as habitat associations of the queen morphs. We do this by sampling established queens from a large number of excavated nests from several populations, estimating genetic relatedness among coexisting queens and pitfall trapping free-ranging wingless queens. 3. Our results show that associations of queen morphs with colony queen number and nest-founding strategy holds only partly. The morph frequencies vary widely across populations from practically pure macrogyne to more than 50% microgyne, but the expected association of macrogyne occurrence with monogyny and microgyne with polygyny is not universal. Dispersal and queen recruitment patterns also show that although most macrogynes participate in nuptial flights and most microgynes are recruited back to their natal nests, a fraction of both morphs use the alternative strategy. 4. The polygynous microgyne morph has been suggested to specialize in stable habitats, but our results from Finnish mesic heath forests do not support this. This study shows that factors other than just queen size also influence life-history trait variation and reproductive strategies in ants.
  • Wang, Yingying X. G.; Matson, Kevin D.; Santini, Luca; Visconti, Piero; Hilbers, Jelle P.; Huijbregts, Mark A. J.; Xu, Yanjie; Prins, Herbert H. T.; Allen, Toph; Huang, Zheng Y. X.; de Boer, Willem F. (2021)
    As a source of emerging infectious diseases, wildlife assemblages (and related spatial patterns) must be quantitatively assessed to help identify high-risk locations. Previous assessments have largely focussed on the distributions of individual species; however, transmission dynamics are expected to depend on assemblage composition. Moreover, disease-diversity relationships have mainly been studied in the context of species loss, but assemblage composition and disease risk (e.g. infection prevalence in wildlife assemblages) can change without extinction. Based on the predicted distributions and abundances of 4466 mammal species, we estimated global patterns of disease risk through the calculation of the community-level basic reproductive ratio R0, an index of invasion potential, persistence, and maximum prevalence of a pathogen in a wildlife assemblage. For density-dependent diseases, we found that, in addition to tropical areas which are commonly viewed as infectious disease hotspots, northern temperate latitudes included high-risk areas. We also forecasted the effects of climate change and habitat loss from 2015 to 2035. Over this period, many local assemblages showed no net loss of species richness, but the assemblage composition (i.e. the mix of species and their abundances) changed considerably. Simultaneously, most areas experienced a decreased risk of density-dependent diseases but an increased risk of frequency-dependent diseases. We further explored the factors driving these changes in disease risk. Our results suggest that biodiversity and changes therein jointly influence disease risk. Understanding these changes and their drivers and ultimately identifying emerging infectious disease hotspots can help health officials prioritize resource distribution.
  • Laakkonen, Hanne; Happonen, Juha-Matti; Marttinen, Eino; Paganus, Aila; Holtta, Tuula; Holmberg, Christer; Rönnholm, Kai (2010)
  • Bradshaw, Corey J. A.; Johnson, Christopher N.; Llewelyn, John; Weisbecker, Vera; Strona, Giovanni; Saltre, Frederik (2021)
    The causes of Sahul's megafauna extinctions remain uncertain, although several interacting factors were likely responsible. To examine the relative support for hypotheses regarding plausible ecological mechanisms underlying these extinctions, we constructed the first stochastic, age-structured models for 13 extinct megafauna species from five functional/taxonomic groups, as well as 8 extant species within these groups for comparison. Perturbing specific demographic rates individually, we tested which species were more demographically susceptible to extinction, and then compared these relative sensitivities to the fossil-derived extinction chronology. Our models show that the macropodiformes were the least demographically susceptible to extinction, followed by carnivores, monotremes, vombatiform herbivores, and large birds. Five of the eight extant species were as or more susceptible than the extinct species. There was no clear relationship between extinction susceptibility and the extinction chronology for any perturbation scenario, while body mass and generation length explained much of the variation in relative risk. Our results reveal that the actual mechanisms leading to the observed extinction chronology were unlikely related to variation in demographic susceptibility per se, but were possibly driven instead by finer-scale variation in climate change and/or human prey choice and relative hunting success.
  • Horppila, Jukka; Härkönen, Laura; Hellén, Noora; Estlander, Satu; Pekcan-Hekim, Zeynep; Ojala, Anne (2019)
    The effects of water turbulence on rotifer communities were experimentally studied under different predation pressures. When the larvae of the phantom midge (Chaoborus flavicans) were present in turbulent water, the abundance of most rotifer taxa was enhanced. Especially the genera Chromogaster, Keratella, Polyarthra, and Trichocerca, increased in abundance. In calm water, chaoborids did not affect the rotifer community. In turbulent water predation by chaoborids was targeted more towards cladocerans (Bosmina sp.) and predation pressure on rotifers was relaxed. Additionally, reduced competition with cladocerans probably contributed to the increase of rotifer abundance. Turbulence alone had no significant effect on rotifer abundance because their individual size was small compared with the diameter of the turbulent eddies. The study suggested that the effects of turbulence on rotifers is not direct but takes place through changed predator-prey relations, i.e., the effect depends on the abundance of invertebrate predators. In aquatic ecosystems with a high density of chaoborids, increasing turbulence can considerably increase the abundance of rotifers.