Resource modification by ecosystem engineers generates hotspots of stream community assembly and ecosystem function

Ecosystem engineers can generate hotspots of ecological structure and function by facilitating the aggregation of both resources and consumers. However, nearly all examples of such engineered hotspots come from long-lived foundation species, such as marine and freshwater mussels, intertidal cordgrasses, and alpine cushion plants, with less attention given to small-bodied and short-lived animals. Insects often have rapid life cycles and high population densities and are among the most diverse and ubiquitous animals on earth. Although these taxa have the potential to generate hotspots and heterogeneity comparable to that of foundation species, few studies have examined this possibility. We conducted a mesocosm experiment to examine the degree to which a stream insect ecosystem engineer, the net-spinning caddisfly (Tricoptera:Hydropsychidae), creates hotspots by facilitating invertebrate community assembly. Our experiment used two treatments: (1) stream benthic habitat with patches of caddisfly engineers present and (2) a control treatment with no caddisflies present. We show that compared to controls, caddisflies increased local resource availability measured as particulate organic matter (POM) by 43%, ecosystem respiration (ER) by 70%, and invertebrate density, biomass and richness by 96%, 244%, and 72%, respectively. These changes resulted in increased spatial variation of POM by 25%, invertebrate density by 76%, and ER by 29% compared to controls, indicating a strong effect of caddisflies on ecological heterogeneity. We found a positive relationship between invertebrate density and ammonium concentration in the caddisfly treatment, but no such relationship in the control, indicating that either caddisflies themselves or the invertebrate aggregations they create increased nutrient availability. When accounting for the amount of POM, caddisfly treatments increased invertebrate density by 48% and richness by 40% compared to controls, suggesting that caddisflies may also enhance the nutritional quality of resources for the invertebrate assemblage. The caddisfly treatment also increased the rate of ecosystem respiration as a function of increasing POM compared to the control. Our study demonstrates that insect ecosystem engineers can generate heterogeneity by concentrating local resources and consumers, with consequences for carbon and nutrient cycling.

Effects of exogenous lanthanum(III) exposure on the positive interaction between mutually beneficial populations

Rare earth elements (REEs) are widely used in various fields, and their accumulation has been reported to pose environmental risks. Most studies confirmed the damage of excessive REE exposure to individual plants; however, little attention has been given to their effects on plant populations. A positive interaction indicates a mutually beneficial relationship between two populations, which is beneficial to the survival and growth of the populations. However, it remains unknown whether exogenous REEs affect the positive interactions between populations. This study investigated the effects of exogenous lanthanum(III) [La(III)] exposure on the positive interaction between soybean (Glycine max L.) and wheat (Triticum aestivum L.) populations by their modules. At normal nutrient level (½-strength Hoagland), the inhibition of excessive La(III) on population modules decreased with increasing population density. Decreases of 39.26 to 1.05% for soybean and 41.45 to 2.41% for wheat indicated the inhibition of La(III) on the positive interaction of both populations weakened with increasing population density. At low nutrient level (¼-strength Hoagland), the inhibition of excessive La(III) on population modules increased with increasing population density. Decreases of 5.82-57.14% for soybean and 4.22-59.04% for wheat indicated the inhibition of La(III) on the positive interaction of both population was strengthened with increasing population density. In summary, the inhibitory effects of exogenous La(III) exposure on the positive interaction between populations vary with both nutrient level and population density. This is a new factor that needs to be considered when evaluating the safety risks of REEs in the environment.

Nest Concealment and Nest Defence by Two Passerines: Effect of Protective Nesting Association

Selection of favourable micro-habitat conditions at nest-sites and nest defence can be important anti- predatory strategies in open-cup nesting birds. In response to nest predation risks, some species of birds appear to form protective nesting associations in which both may gain benefits due to mutual warning and nest defence. Despite the many studies assessing the impact of various factors on nest defence and nest placement, how interactions between species while breeding can modify these strategies is still poorly understood. Here I evaluate whether nesting associations in two species influence nest defence intensity and nest-site selection. An observational approach was used to analyse the defensive behaviours of the Barred Warbler Sylvia nisoria and Red-backed Shrike Lanius collurio in an agricultural landscape in eastern Poland. Association was determined by the position of the nest with respect to that of the associated species (by the nest of one species being within the breeding territory of the other). Nest defence behaviour of these two passerines was assessed as their response to a human intruder near an active brood. This study showed that the nest size and visibility were similar in nest-sites of pairs nesting in association and in spatial isolation. Barred Warblers nesting within shrike breeding territories strongly defended their nests. Warblers breeding alone displayed a lower level of defence than birds nested in association. Shrikes not nesting with warblers were significantly more aggressive than those breeding in the protective nesting association. I suggest that shrikes tried to compensate for the lack of assistance by warblers in joint nest defence and were forced to invest more into defending their own nests. This research suggests that positive interactions within the heterospecific network of relations in ecosystems may be one of the factors responsible for diversifying the intensity of avian nest defence.

The mechanisms by which oysters facilitate invertebrates vary across environmental gradients

The effective use of ecosystem engineers to conserve biodiversity requires an understanding of the types of resources an engineer modifies, and how these modifications vary with biotic and abiotic context. In the intertidal zone, oysters engineer ecological communities by reducing temperature and desiccation stress, enhancing the availability of hard substrate for attachment, and by ameliorating biological interactions such as competition and predation. Using a field experiment manipulating shading, predator access and availability of shell substrate at four sites distributed over 900 km of east Australian coastline, we investigated how the relative importance of these mechanisms of facilitation vary spatially. At all sites, and irrespective of environmental conditions, the provision of hard substrate by oysters enhanced the abundance and richness of invertebrates, in particular epibionts (barnacles and oyster spat) and grazing gastropods. Mobile arthropods utilised the habitat provided by disarticulated dead oysters more than live oyster habitat, whereas the abundance of polychaetes and bivalves were much greater in live oysters, suggesting the oyster filter-feeding activity is important for these groups. In warmer estuaries, shading by oysters had a larger effect on biodiversity, whereas in cooler estuaries, the provision of a predation refuge by oysters played a more important role. Such knowledge of how ecosystem engineering effects vary across environmental gradients can help inform management strategies targeting ecosystem resilience via the amelioration of specific environmental stressors, or conservation of specific community assemblages.

Couples' relationship affects mothers' and fathers' anxiety and depression trajectories over the transition to parenthood

BACKGROUND

The association between the couple relationship and the mothers' and fathers' psychological adjustment to the transition to parenthood has been examined in the literature. However, the direction of effects between these variables has not been extensively explored. This study aimed to assess the direction of effects between mothers' and fathers' positive and negative interactions and anxiety and depression symptoms trajectories over the transition to parenthood.

METHODS

A sample of 129 couples (N = 258) completed self-report measures of positive and negative interactions, anxiety and depression symptoms at each trimester of pregnancy, at childbirth, and at 3- and 30-months postpartum. Dyadic growth curve models were performed using multilevel modeling.

RESULTS

Whereas anxiety and depression showed no moderation effect on positive and negative interactions over time, negative interaction moderated depression from 3- to 30-months postpartum. Mothers and fathers with high negative interaction scores experienced a steeper increase in depression from 3- to 30-months postpartum. Additionally, gender moderated the effect of positive interaction on anxiety from 3- to 30-months postpartum. Fathers with low positive interaction scores experienced an increase in anxiety, whereas fathers with high positive interaction scores and mothers with high or low positive interaction scores did not experience changes in anxiety from 3- to 30-months postpartum.

LIMITATIONS

Despite the longitudinal aspect of the models, a possible causal relationship need to be taken with caution.

CONCLUSIONS

Our results suggest that mothers' and fathers' positive and negative interactions affect their anxiety and depression symptoms trajectories: negative interaction raises mothers' and fathers' depression symptoms and positive interaction prevents the increase of fathers' anxiety symptoms over the postpartum period.

Interactions among competing nematode species affect population growth rates

Investigations of the interplay of organisms in an ecological community are a prerequisite to understanding the processes that shape the structures of those communities. Among several types of interactions, interest in the positive interactions of species that compete for the same resource has grown, as they may provide a mechanism enabling coexistence. In the laboratory experiment described herein, the effects of interspecific interaction on the population growth of two bacterial-feeding nematode species, Panagrolaimus cf. thienemanni and Poikilolaimus cf. regenfussi, were investigated. Specifically, we asked: (1) whether there is an interspecific interaction between organisms competing for a mutual resource and (2) whether these interactions are altered by the competitors' initial densities and (3) their variable growth rates (induced by different food supplies). Each treatment initially contained 48 nematode individuals, but at different species ratios (48:0; 32:16; 24:24; 16:32; 0:48). The populations were provided with three different bacterial densities (10⁸, 10⁹, and 10¹⁰ cells ml^-1) as food. The data were analyzed using a generalized linear mixed model. The best-fitting model revealed a significant decline in population growth rates with an increasing species ratio, but depending on the food density and species. These results provide strong evidence for positive interspecific interactions that vary with both species density and food-supply level. They also suggest important roles for positive interspecific interactions in habitat colonization and in maintaining the coexistence of species in the same trophic group.

Interaction between castanospermine an immunosuppressant and cyclosporin A in rat cardiac transplantation

AIM: To investigate the interaction between castanospermine and cyclosporin A (CsA) and to provide an explanation for it.

METHODS: The alkaloid castanospermine was prepared from the seeds of Castanospermum austral consistently achieving purity. Rat heterotopic cardiac transplantation and mixed lymphocyte reactivity were done using genetically inbred strains of PVG (donor) and DA (recipient). For the mixed lymphocyte reaction stimulator cells were irradiated with 3000 rads using a linear accelerator. Cyclosporin A was administered by gavage and venous blood collected 2 h later (C₂). The blood levels of CsA (Neoral) were measured by immunoassay which consisted of a homogeneous enzyme assay (EMIT) on Cobas Mira. Statistical analyses of interactions were done by an accelerated failure time model with Weibull distribution for allograft survival and logistic regression for the mixed lymphocyte reactivity.

RESULTS: Castanospermine prolonged transplant survival times as a function of dose even at relatively low doses. Cyclosporin A also prolonged transplant survival times as a function of dose particularly at doses above 2 mg/kg. There were synergistic interactions between castanospermine and CsA in the prolongation of cardiac allograft survival for dose ranges of CsA by castanospermine of (0 to 2) mg/kg by (0 to 200) mg/kg (HR = 0.986; 95%CI: 0.981-0.992; P < 0.001) and (0 to 3) mg/kg by (0 to 100) mg/kg (HR = 0.986; 95%CI: 0.981-0.992; P < 0.001) respectively. The addition of castanospermine did not significantly increase the levels of cyclosporin A on day 3 or day 6 for all doses of CsA. On the contrary, cessation of castanospermine in the presence of CsA at 2 mg/kg significantly increased the CsA level (P = 0.002). Castanospermine inhibited mixed lymphocyte reactivity in a dose dependent manner but without synergistic interaction.

CONCLUSION: There is synergistic interaction between castanospermine and CsA in rat cardiac transplantation. Neither the mixed lymphocyte reaction nor the metabolism of CsA provides an explanation.