Limited niche differentiation within remarkable co‐occurrences of congeneric species: Monomorium ants in the Australian seasonal tropics

Niche theory predicts that few closely related species can co‐occur because such species tend to be ecologically similar and niche differentiation is required to avoid competitive exclusion. We analyse the co‐occurrence of a remarkable 10–15 species of the ant genus Monomorium occurring within single 10 × 10 m plots in a tropical savanna of northern Australia. Most of the species are undescribed, so we use genetic analysis to validate our species demarcations. We document nest dispersion patterns, and investigate differentiation in the three primary niche dimensions: space, time and food. We also examine species differences in competitive abilities, by describing rates of foraging activity, foraging ranges, worker aggression, and levels of behavioural dominance. Analyses of nest and forager distributions showed very limited evidence of spatial segregation within plots. The great majority of species foraged either exclusively or primarily during daylight hours. Body size and isotopic analyses indicated very limited dietary differentiation. Such limited niche partitioning occurred despite the species differing markedly in their competitive abilities as measured by rates of resource discovery, recruitment and monopolization. Our findings defy the traditional assumption that multiple closely related and ecologically similar species of highly interactive taxa cannot co‐occur. It seems very likely that species coexistence in our study system is determined to a very large degree by stochastic processes relating to dispersal and establishment, as predicted by neutral theory. However, neutral theory assumes competitive equivalence, whereas we found very marked differences in the competitive abilities of our co‐occurring species. We suggest that competitive exclusion is prevented by the modular nature of ant colonies, with competition limiting colony performance but not preventing occurrence. We conclude that other factors that allow species persistence, and not just competitive equivalence, can allow dispersal and establishment processes to drive species coexistence.     

Characterization of 59 canine single nucleotide polymorphisms in the Italian wolf (Canis lupus) population

We characterized 59 canine single nucleotide polymorphisms (SNPs) in the endangered Italian wolf (Canis lupus) population, which were discovered by resequencing sequence‐tagged‐site (STS) DNA sequences that are known to contain SNPs in domestic dogs. Dog SNPs were usually found also in wolves. Additional SNPs unique in dogs or wolves were discovered, which is important for detecting hybrids between dogs and wolves. We developed new primer sets and analysed 15 SNPs by Pyrosequencing. The characterized SNPs will provide an important addition to the genetic markers that are currently available for studying wild populations of canids.     

Efficiency of selection, as measured by single nucleotide polymorphism variation, is dependent on inbreeding rate in Drosophila melanogaster

It is often hypothesized that slow inbreeding causes less inbreeding depression than fast inbreeding at the same absolute level of inbreeding. Possible explanations for this phenomenon include the more efficient purging of deleterious alleles and more efficient selection for heterozygote individuals during slow, when compared with fast, inbreeding. We studied the impact of inbreeding rate on the loss of heterozygosity and on morphological traits in Drosophila melanogaster. We analysed five noninbred control lines, 10 fast inbred lines and 10 slow inbred lines; the inbred lines all had an expected inbreeding coefficient of approximately 0.25. Forty single nucleotide polymorphisms in DNA coding regions were genotyped, and we measured the size and shape of wings and counted the number of sternopleural bristles on the genotyped individuals. We found a significantly higher level of genetic variation in the slow inbred lines than in the fast inbred lines. This higher genetic variation was resulting from a large contribution from a few loci and a smaller effect from several loci. We attributed the increased heterozygosity in the slow inbred lines to the favouring of heterozygous individuals over homozygous individuals by natural selection, either by associative over‐dominance or balancing selection, or a combination of both. Furthermore, we found a significant polynomial correlation between genetic variance and wing size and shape in the fast inbred lines. This was caused by a greater number of homozygous individuals among the fast inbred lines with small, narrow wings, which indicated inbreeding depression. Our results demonstrated that the same amount of inbreeding can have different effects on genetic variance depending on the inbreeding rate, with slow inbreeding leading to higher genetic variance than fast inbreeding. These results increase our understanding of the genetic basis of the common observation that slow inbred lines express less inbreeding depression than fast inbred lines. In addition, this has more general implications for the importance of selection in maintaining genetic variation.     

Immediate effects of Ore on ants in the semi-arid mallee region of north-western Victoria

The immediate effects of a high intensity wildfire on the ant communities of a heath and a mallee site in semi-arid north-western Victoria are reported. Following fire the number of species trapped on the ground doubled (to ca. 80 each site), total ant abundance decreased by half (due to the demise of previously dominant species), surface activity of reproductive castes increased, and dramatic changes in species relative abundance (including shifts toward greater equitability) occurred. These changes are interpreted in terms of fire-induced simplification of the habitat and release from competition with dominant species. The results appear to illustrate the importance of interspecific competition in structuring foraging activity in mallee ant communities. Observations are also reported on seed-harvesting by ants, including changes in harvester ant abundance, germination from within-nest seed storage, and the first record of Heteroponera removing seeds.     

Entrainment of Geotropic Oscillations in Hypocotyls of Helianthus annuus– An Experimental and Theoretical Investigation

The effects of periodically repeated geotropic stimulations (geotropic pulses) on sunflower hypocotyls are studied. The experimental results agree with predictions from a theory for geotropic movements of the hypocotyl. A sunflower hypocotyl performs circumnutations around or across the plumb line with a period of about 2.5 hours. These oscillations can be entrained to periodically repeated geotropic pulses with a period in a region around 2.5 hours. The limits of this “region of entrainment’ for geotropic pulses are studied. In the region of entrainment resonance curves, i.e., the amplitude of the oscillations plotted as a function of the period of the geotropic pulses, are obtained. The phase differences (measured as time differences) between the geotropic pulse rhythms and the resulting oscillations are also studied. Beat phenomena are predicted and recorded outside the region in which the plants can be entrained. The results are discussed in relation to oscillating phenomena of circadian type (i.e., with a period close to 24 hours), and many similarities are pointed out.     

Nuisance growth of Juncus bulbosus: the roles of genetics and environmental drivers tested in a large‐scale survey

1. Invasive species can transform aquatic ecosystems, and the nuisance growth of the freshwater macrophyte Juncus bulbosus has become a problem in many lakes and rivers in northern Europe. It affects biodiversity strongly and conflicts with human uses, not least compromising the generation of hydroelectricity. The causes of the proliferation of these massive stands of J. bulbosus are not finally resolved, however. 2. In this study, a wide range of catchment, lake and sediment parameters (n = 34) were assessed for 139 lakes in Southern Norway, with the aim of explaining the presence or absence of J. bulbosus and to assess potential drivers behind its prolific growth. 3. Juncus bulbosus was more often present in lakes with lower pH and phosphate concentrations, and a higher element ratio of dissolved inorganic nitrogen (DIN) to total phosphorus (DIN : TotP). 4. Despite the many parameters measured across substantial environmental gradients, none explained nuisance growth. Genetic screening (amplified fragment length polymorphism fingerprinting) of plants from a subset of lakes and additional river sites also showed no genetic differences between the various growth forms. A macrophyte trophic index, however, suggested that the most problematic growth occurred in the most oligotrophic lakes. 5. The lack of consistent patterns may reflect either factors not assessed in our survey, or that the current extension of stands represents a gradual cumulative response over time, not characterised effectively in our snapshot survey. Nevertheless, we can now exclude some putative causes of nuisance growth, including in particular genetics and N‐deposition.