Generalist dung attraction response in a New Zealand dung beetle that evolved with an absence of mammalian herbivores

1. Dung beetles (Scarabaeidae: Scarabaeinae) are integral parts of many ecosystems because of their role in decomposition of dung; particularly mammal dung, which forms the diet of both larvae and adults. 2. New Zealand dung beetles are unusual as they are flightless and evolved on islands with a highly depauperate mammal fauna and thus without the usual dung resource used by dung beetles elsewhere. The diet of New Zealand dung beetles is unknown. 3. We hypothesised (1) that the endemic dung beetle Saphobius edwardsi would be attracted to a broad range of food types, and (2) that S. edwardsi would be able to survive and reproduce on a range of dung types and puriri (Vitex lucens) humus. 4. Laboratory choice tests identified that S. edwardsi was attracted to a range of mammal, bird, invertebrate, and reptile dung types, but not to non‐dung food sources. Five‐month no‐choice tests found that beetle survival rates were lower for beetles fed with humus compared with those fed on mammal, bird, or invertebrate dung. None of the beetles reproduced. 5. This study suggests S. edwardsi have a strong preference for dung, and are likely to be broad dung generalists in their feeding behaviour.     

Metabolic factors influencing the sodium and potassium distribution in Ulva lactuca

1. Methods for the use of the marine green alga, Ulva lactuca, in studies on electrolyte metabolism are described. 2. The effect of illumination and iodoacetate on the potassium and sodium content, as well as the influence of light and running sea water on the iodoacetate effect was investigated. The rate of exchange of cellular potassium ion for K(42) under conditions of light and dark at 20 and 30 degrees C. was studied. 3. Ulva maintained in the dark for long periods loses some potassium and gains sodium, both effects being reversed upon illumination. The presence of 0.001 M iodoacetate in the dark causes a marked progressive loss of potassium and gain of sodium, phenomena which do not occur when the alga is illuminated. Evidence for the penetration of the inhibitor into the cell in the presence of light is presented. The iodoacetate effect on potassium and sodium content, once established, can be "washed out" of the alga when the plant is placed in light and running sea water without the inhibitor. Illumination and increased temperature each favor a more rapid exchange of tissue for environmental potassium ion. 4. In the interpretation of these findings it is emphasized that metabolic work, perhaps in the form of ion transports, must be done by the cell to compensate for the continual flow of potassium ion and sodium ion with their respective concentration gradients and thus maintain homeostasis within the cell. Evidence is presented which indicates separate mechanisms for the distribution of sodium and potassium in this organism. It is further suggested that the degradation of phosphoglyceric acid, an important glycolytic and photosynthetic intermediate, or one of the products of its metabolism supplied the energy for these ion transports(s). The role of permeability per se is considered.     

GLOCHIDIA OF THE FRESHWATER MUSSEL LAMPSILIS OVERWINTERING ON FISH HOSTS

Largemouth Bass were infected with glochidia of the freshwatermussel Lampsilis cardium. Three fishes each were held at 4.5,10, and 15.5°C; five fish were held at 21°C. By 64 days,metamorphosed juveniles were found in the 15.5 and 21°Ctrials but not in the 5.5 and 10°C trials, indicating thatthe lower threshold temperature for metamorphosis was between10 and 15.5°C for the duration. In a second experiment,Largemouth Bass were infected with glochidia of L. cardium andheld at 10°C. A sample of fishes was removed monthly andbrought to 21°C. Numbers of glochidia that metamorphosedafter being warmed were compared to the number that metamorphosedwithout warming. The percentage that metamorphosed after warmingdecreased linearly with time. At one month, 100% of the glochidiametamorphosed after warming. This decreased to 80% by two months,to 30% by four months and 3% by six months. Although this post-warmingpercentage decreased with time, the total percentage of metamorphosedjuveniles (at all temperatures) was not correlated with time.Controls kept at 21°C required three weeks to reach peakmetamorphosis, but test subjects subjected to 10°C requiredless than nine days to metamorphose once warmed. Many overwinteringglochidia therefore complete a portion of their developmenton the host at winter temperatures, but stop short of excystment.Some glochidia metamorphosed without being warmed, but thisphenomenon is not understood. This study confirms that glochidiamay overwinter on hosts, with some glochidia persisting formore than six months before metamorphosing when warmer conditionsreturn. (Received 29 September 1998; accepted 18 January 1999)     

Variability of Relationships between Transpiration, Shoot and Root Metabolism, and Nutrient Uptake in Intact Plants

Reasons are given for rejecting recent criticisms of methodsused in earlier work on relationships between transpirationand the transfer of nutrients to the shoots of intact plants.     

Myrmecochory in Australia's seasonal tropics: Effects of disturbance on distance dispersal

Abstract Successful ecosystem restoration requires the re-establishment of fundamental ecological processes, many of which involve plant-animal interactions. Myrmecochory (seed dispersal by ants) is a particularly important plant-animal mutualism in Australia, but little is known about its response to either disturbance or restoration following disturbance. Here we investigate the effects of disturbance on seed dispersal by ants, and the extent to which the ant-seed relationship has re-established at sites undergoing rehabilitation, at Ranger uranium mine in the seasonal tropics of Australia's Northern Territory. We focused on the composition of seed-dispersing ant assemblages, rates of seed removal by ants, and the dispersal curves generated by ants, as determined by observations of removal from seed depots. Ten sites were studied, comprising four ‘natural’ (undisturbed) sites representing a range of savanna habitats occurring in the region, four disturbed sites representing a range of habitat disturbance but with intact soil, and two waste rock sites subject to preliminary revegetation trials. A total of 22 ant species from 10 genera were observed during 154 observations of seed removal, most commonly Rhytidoponera aurata (53 records), Monomorium (rothsteini gp) sp. 1 (14), Iridomyrmex sanguineus (13), Iridomyrmex pallidus (12) and Pleidole sp. 3 (10). Removal rates (over 3 h) averaged 29% across all sites and time periods, varying markedly both between and within sites. However, mean rates of removal were similar between natural, disturbed and waste rock sites (29%, 28% and 31%, respectively). A high incidence (62% of all depots) of'aril robbing’ by ants (primarily Monomorium spp.) eating arils in situ, without removal, was observed. Dispersal distances varied markedly between ant species, with Iridomyrmex sanguineus having both the highest mean (7.25m) and maximum (13.08 m) dispersal distances. Species of Pheidole typically dispersed seeds less than 0.5 m, and Meranoplus, Monomorium and Tetramorium spp. only ever moved seeds a few centimetres, usually dropping and abandoning them before reaching the nests. The dispersal curves characteristic of each site varied markedly due to the different composition of seed-dispersing ants. The mean dispersal distance at disturbed sites (3.91 m) was significantly higher than at natural sites (2.19 m), and the curves were strongly skewed in the former, but relatively uniform in the latter. The implications of these differences for recovery following disturbance are unclear. At rehabilitated waste rock sites, all observed removals involved distances less than 0.5 m, with a mean of 17 cm. This lack of effective ant-seed relationships might represent a barrier to further vegetation development at rehabilitated sites.