Habitat variation,mutualism and predation shape the spatio‐temporal dynamics of tansy aphids

1. Spatially distributed resources can lead to the formation of metapopulations, where individual subpopulations are often small and can experience frequent local extinction events followed by recolonisation. An example of terrestrial metapopulations are specialised phytophagous insects on their patchily distributed host plants. 2. The present study investigated the population dynamics of a specialised aphid (Metopeurum fuscoviride) on its patchily distributed host plant (Tanacetum vulgare) and associated community of mutualistic ants and predators in a small‐scale field site. Furthermore, aphid habitat differences (plant size, C/N ratio, location and surrounding vegetation) were quantified, and seasonal timing and precipitation were considered. 3. Seasonal timing and precipitation both had effects on aphid colonisation, extinction events and aphid colony persistence. Towards the end of the season, and after higher precipitation, aphid colonisation events decreased and extinction events increased. Plant size and location as well as aphid within‐field dispersal determined the spatio‐temporal distribution of aphid colonies. 4. Mutualistic ants (Lasius niger and Myrmica rubra) increased the chance of establishment of aphid colonies. However, when M. rubra was tending, aphid colony persistence was reduced. Aphid persistence and extinction were dependent on aphid abundance, as a higher colony size reduced the probability of extinction by predation. 5. The results emphasise the importance of dispersal limitation, population growth and the presence of mutualists when studying the spatio‐temporal dynamics of tansy aphids, particularly in a small‐scale field site.     

Increased nest cofounding and high intra-colony relatedness in the bee Exoneura bicolor (Hymenoptera: Apidae): Results from an experimental situation

Abstract Identifying differences in a key social trait between two populations of die same species is important for understanding the evolution of sociality. Previous studies of new colonies in Exoneura bicolor, an Australian allodapine bee, have shown that there are high levels of kin cofounding in a montane population. The only study to examine intra-colony relatedness in a heathland population has found that new multifemale colonies are not formed by kin. In this study we used an experiment to investigate both cofounding behaviour and intra-colony relatedness in E. bicolor from a heathland population. Nest substrate was placed either 0.05 or 1 m distant from source nests in a novel environment. Although there were no differences in cofounding rate or intra-colony relatedness between die two treatments there was, overall, a high rate of cofounding: 53% of new nests were multifemale, approximately twice as high as found in previous field-based studies. Relatedness among cofoundresses was not only different from zero, ^r± SE = 0.597 ± 0.097, but almost identical to that found in montane populations. A constraint, such as nest substrate distribution, is suggested as a proximate factor affecting the expression of cofounding behaviour in E. bicolor. The implication of such proximate constraints for inferring the phylogenetic origins of social behaviour is discussed.     

The role of photosynthesis/light relationships in determining lower depth limits of Characeae in South Island, New Zealand lakes

1. The maximum depth of colonization of aquatic macrophytes ( Z _c) was investigated in eighteen South Island, New Zealand lakes. The downward attenuation coefficient for photosynthetically active radiation ( K _d(PAR)) was calculated and the spectral characteristics of the lakes determined with a spectroradiometer.
2. Characean algae dominated the deepest communities in sixteen of the study lakes.
3. Z _c was significantly related to K _d(PAR) by the relationship Z _c = 4.5/ K _d– 2.2.
4. From measurements of the photosynthetic properties of Chara corallina (Kl. ex Willd., em R.D.W.) and incident radiation over the course of a year we calculated the depth at which daily net photosynthesis would be equal to zero for each day of the year. An annual average of this depth was significantly related to Z _c with an r 2 of 0.86.
5. Correcting K _d(PAR) for spectral quality and taking into account the potential absorption spectrum of a characean meadow did not improve the relationships.
6. We suggest that relationships established between K _d(PAR) and Z _c of characean algae in South Island, New Zealand lakes can be explained to a great extent by light limitation of photosynthesis.     

Population affinities of the asiatic cobra (Naja naja) species complex in south-east Asia: reliability and random resampling

The population systematics of the cobras of the genus Naja in southern Thailand, Malaysia and Indonesia are investigated, using multivariate analysis of a large number of morphological characters. These populations are found to constitute three distinct groups: a northern form, which occurs in Thailand and northern Peninsular Malaysia; an equatorial form, which occurs in southern Thailand, Peninsular Malaysia, Sumatra and Borneo; and a southern form, which occurs on Java and the Lesser Sunda Islands. The first two forms are sympatric in northern Peninsular Malaysia and southern Thailand, and therefore constitute separate species. This is of importance for the treatment of snakebite in the region. The distribution of the three forms can be related both to present ecological conditions and to Pleistocene geological and climatic events. The reliability of the results is demonstrated by the relationship between character number and congruence of patterns of geographic variation, investigated by random resampling. The pattern of geographic variation within two of the three main forms is investigated and related to current ecological conditions and Pleistocene events.