Biophysical feedback mediates effects of invasive grasses on coastal dune shape

Vegetation at the aquatic-terrestrial interface can alter landscape features through its growth and interactions with sediment and fluids. Even similar species may impart different effects due to variation in their interactions and feedbacks with the environment. Consequently, replacement of one engineering species by another can cause significant change in the physical environment. Here we investigate the species-specific ecological mechanisms influencing the geomorphology of U.S. Pacific Northwest coastal dunes. Over the last century, this system changed from open, shifting sand dunes with sparse vegetation (including native beach grass, Elymus mollis), to densely vegetated continuous foredune ridges resulting from the introduction and subsequent invasions of two nonnative grass species (Ammophila arenaria and Ammophila breviligulata), each of which is associated with different dune shapes and sediment supply rates along the coast. Here we propose a biophysical feedback responsible for differences in dune shape, and we investigate two, non-mutually exclusive ecological mechanisms for these differences: (1) species differ in their ability to capture sand and (2) species differ in their growth habit in response to sand deposition. To investigate sand capture, we used a moveable bed wind tunnel experiment and found that increasing tiller density increased sand capture efficiency and that, under different experimental densities, the native grass had higher sand capture efficiency compared to the Ammophila congeners. However, the greater densities of nonnative grasses under field conditions suggest that they have greater potential to capture more sand overall. We used a mesocosm experiment to look at plant growth responses to sand deposition and found that, in response to increasing sand supply rates, A. arenaria produced higher-density vertical tillers (characteristic of higher sand capture efficiency), while A. breviligulata and E. mollis responded with lower-density lateral tiller growth (characteristic of lower sand capture efficiency). Combined, these experiments provide evidence for a species-specific effect on coastal dune shape. Understanding how dominant ecosystem engineers, especially nonnative ones, differ in their interactions with abiotic factors is necessary to better parameterize coastal vulnerability models and inform management practices related to both coastal protection ecosystem services and ecosystem restoration.     

Distribution of Pb,Cr, Cu and Zn in the marine-coastal region of Zanzibar (Tanzanian archipelago,East Africa)

In Tanzania, a large amount of domestic and industrial wastes are daily released to the aquatic environment without prior treatment. The present paper establishes the status of distribution and environmental implications of heavy metals in water, sediment, suspended particulate matter and biota (Anadara antiquata) from two marine coasts in Zanzibar, Tanzania. These metals are derived from the industrial areas through rivers and storm water outflows. Heavy metal concentrations in the collected samples were determined using atomic absorption spectrophotometry. Concentrations were significantly higher in the Malindi compared to the Fumba coast (ANOVA, p?=?.001). Calculation of metal partition coefficients shows that the relative importance of the particulate and the water phases varies in response to water parameters and suspended solid content, but that most elements achieve a conditional equilibrium in these coasts. Higher metal concentrations found in Malindi suggest a pollution effect related to anthropogenic activities. Mean metal burdens in the tissues of A. antiquata from both Malindi and Fumba coasts were significantly higher than in other compartments analysed (ANOVA, p?<.05). Maximum values of contamination factor and contamination degree for metals were noticed for sediments from both Malindi and Fumba coasts. It is imperative to understand that metal concentrations of coastal environments depend not only on industrial and household waste inputs but also on the geochemical composition of the area.     

Chemical basis of nestmate recognition in a defense context in a one-piece nesting termite

Nestmate recognition is a necessary capacity for the occurrence of discrimination between nestmate and non-nestmate individuals. In one-piece nesting termites, which nest and forage in a single piece of wood, nestmate recognition is poorly studied mainly because the probability of encountering exogenous individuals is low in comparison with separate-piece nesting termites. Previous work described that production of soldiers of Neotermes chilensis, a one-piece nesting termite, increased when the risk of invasion of their colony increased, for example when neighboring colonies were present in the same nesting substrate and members of different colonies met when digging galleries. If soldiers are to fulfill their defensive role under these circumstances, they should show nestmate recognition ability; moreover, based on work on other social insects, such nestmate recognition should be based on cuticular compounds (CC). Bioassays were performed in which a soldier of N. chilensis was confronted with a nestmate or non-nestmate primary reproductive, pseudergate or another soldier, and in which a soldier was confronted with untreated and with CC-deprived dead primary reproductives. The results showed that soldiers were indeed more aggressive toward non-nestmates than nestmates for all castes, and that this discrimination was mediated mainly by qualitative (simple matching coefficient) and quantitative (Renkonen index) differences in CC.     

Colour discrimination and associative learning in hatchling lizards incubated at ‘hot’ and ‘cold’ temperatures

The ability of an animal to acquire, process and learn from information in their environment is thought to be fundamental to fitness. We currently have a poor understanding of the learning ability of young animals within the first few months of their life, the types of learning they use and the extent of their learning ability. Furthermore, an animal’s developmental environment, such as nest incubation temperature, may profoundly influence motor and cognitive skills. We first tested the ability of hatchling three-lined skinks (Bassiana duperreyi) incubated at ‘hot’ and ‘cold’ temperatures to solve an instrumental (motor) task before assessing their ability to learn colour associations in a multi-stage instrumental task, with a choice reversal. While 53 (88.3 %) lizards successfully completed the training phase, 14 (46.7 %) of the ‘hot’ incubated and none of the ‘cold’ incubated lizards successfully completed the instrumental task. Thirteen of these lizards rapidly learnt to discriminate colours, and this culminated in eight individuals successfully completing a choice reversal. Hatchling B. duperreyi demonstrated surprisingly rapid learning, and these results highlight the potentially important role of cognition during development and ultimately, in fitness.     

Strong responsiveness to noise interference in an anuran from the southern temperate forest

Animals adopt different strategies to communicate by means of sound in noisy environments. Some animals increase, while others decrease, their vocal activity in the presence of interference. Anuran amphibians from diverse latitudes exhibit both kinds of responses. Recent studies have shown that males of Batrachyla taeniata and Batrachyla antartandica from the temperate austral forest do not call in response to the presentation of advertisement calls of sympatric congeneric species, but their responsiveness to other kinds of interference has not been tested. To explore the diversity in responsiveness to acoustic intrusion in a single species, we exposed males of B. taeniata to prolonged prerecorded natural abiotic noises of wind, creek, and rain and to a band-pass noise centered at 2,000 Hz, at 67 dB sound pressure level (SPL). The subjects drastically increased their call rate when exposed to all four sounds. Frogs also responded by augmenting their vocal activity to exposures of band-pass noise at increasing intensities (55–79 dB SPL). The increase in vocal activity in response to noise is strong relative to those of other anurans from the temperate forest studied previously under similar exposures. These results reveal a remarkable activation of vocal response to acoustic interference of continuous abiotic noise, which would allow compensating for limitations in the active communication space under background sounds. This strategy contrasts with the decrease in vocal output amid interference from heterospecific signals reported formerly for this frog, a tactic that would restrict energy expenditure to relevant acoustic competition with conspecifics.