Chilling damage in a changing climate in coastal landscapes of the subtropical zone: a case study from south Florida

Freeze events significantly influence landscape structure and community composition along subtropical coastlines. This is particularly true in south Florida, where such disturbances have historically contributed to patch diversity within the mangrove forest, and have played a part in limiting its inland transgression. With projected increases in mean global temperatures, such instances are likely to become much less frequent in the region, contributing to a reduction in heterogeneity within the mangrove forest itself. To understand the process more clearly, we explored the dynamics of a Dwarf mangrove forest following two chilling events that produced freeze‐like symptoms, i.e., leaf browning, desiccation, and mortality, and interpreted the resulting changes within the context of current winter temperatures and projected future scenarios. Structural effects from a 1996 chilling event were dramatic, with mortality and tissue damage concentrated among individuals comprising the Dwarf forest's low canopy. This disturbance promoted understory plant development and provided an opportunity for Laguncularia racemosa to share dominance with Rhizophora mangle. Mortality due to the less severe 2001 event was greatest in the understory, probably because recovery of the protective canopy following the earlier freeze was still incomplete. Stand dynamics were static over the same period in nearby unimpacted sites. The probability of reaching temperatures as low as those recorded at a nearby meteorological station (≤3 °C) under several warming scenarios was simulated by applying 1° incremental temperature increases to a model developed from a 42‐year temperature record. According to the model, the frequency of similar chilling events decreased from once every 1.9 years at present to once every 3.4 and 32.5 years with 1 and 4 °C warming, respectively. The large decrease in the frequency of these events would eliminate an important mechanism that maintains Dwarf forest structure, and promotes compositional diversity.     

Modelling relationships between birds and vegetation structure using airborne LiDAR data: a review with case studies from agricultural and woodland environments

Airborne LiDAR (Light Detection and Ranging) is a remote sensing technology that offers the ability to collect high horizontal sampling densities of high vertical resolution vegetation height data, over larger spatial extents than could be obtained by field survey. The influence of vegetation structure on the bird is a key mechanism underlying bird–habitat models. However, manual survey of vegetation structure becomes prohibitive in terms of time and cost if sampling needs to be of sufficient density to incorporate fine-grained heterogeneity at a landscape extent. We show that LiDAR data can help bridge the gap between grain and extent in organism–habitat models. Two examples are provided of bird–habitat models that use structural habitat information derived from airborne LiDAR data. First, it is shown that data on crop and field boundary height can be derived from LiDAR data, and so have the potential to predict the distribution of breeding Sky Larks in a farmed landscape. Secondly, LiDAR-retrieved canopy height and structural data are used to predict the breeding success of Great Tits and Blue Tits in broad-leaved woodland. LiDAR thus offers great potential for parameterizing predictive bird–habitat association models. This could be enhanced by the combination of LiDAR data with multispectral remote sensing data, which enables a wider range of habitat information to be derived, including both structural and compositional characteristics.     

Searching for effective indicators of ecosystem function in urban streams: assessing cellulose decomposition potential

1. Urbanisation and landuse changes threaten the ecological integrity of rivers and streams globally. A major challenge in such impacted environments is to develop functional indicators for use by waterway managers. We first reviewed cellulose decomposition potential (CDP) as one such indicator, and here present current understanding and highlight the knowledge gaps which hinder its widespread incorporation into programmes monitoring stream health. In a field study, we also evaluated two differing cellulose materials (Shirley soil burial test material and unbleached calico) and measurement techniques. 2. We also investigated the effects of urbanisation and riparian cover on CDP as a standardised indicator of ecosystem function. Cotton fabrics were deployed in paired open and closed reaches across six stream catchments varying in degree of urbanisation (in south‐eastern Australia). After 7, 14 and 21 days materials were retrieved and their decomposition assessed in conjunction with a number of physicochemical variables. 3. We observed a strong positive relationship between the decomposition of Shirley and calico materials, thus indicating unbleached calico is an effective substitute for Shirley test cloth, which is no longer available. 4. Across sites, CDP was positively correlated with ammonium concentrations and also, to a lesser extent, with filterable reactive phosphorus and sediment silt and clay content/carbon availability. Despite these relationships, cellulose decomposition was not correlated with urbanisation or riparian cover. 5. Cellulose decomposition is a simple, rapid and sensitive functional indicator of water quality and associated anthropogenic landuse changes and is thus a valuable tool for monitoring stream health.     

The genetic architecture of fitness in a seed beetle: assessing the potential for indirect genetic benefits of female choice

Background  

Quantifying the amount of standing genetic variation in fitness represents an empirical challenge. Unfortunately, the shortage of detailed studies of the genetic architecture of fitness has hampered progress in several domains of evolutionary biology. One such area is the study of sexual selection. In particular, the evolution of adaptive female choice by indirect genetic benefits relies on the presence of genetic variation for fitness. Female choice by genetic benefits fall broadly into good genes (additive) models and compatibility (non-additive) models where the strength of selection is dictated by the genetic architecture of fitness. To characterize the genetic architecture of fitness, we employed a quantitative genetic design (the diallel cross) in a population of the seed beetle Callosobruchus maculatus, which is known to exhibit post-copulatory female choice. From reciprocal crosses of inbred lines, we assayed egg production, egg-to-adult survival, and lifetime offspring production of the outbred F1 daughters (F1 productivity).     

Are QST–FST comparisons for natural populations meaningful?

Comparisons between putatively neutral genetic differentiation amongst populations, F_ST, and quantitative genetic variation, Q_ST, are increasingly being used to test for natural selection. However, we find that approximately half of the comparisons that use only data from wild populations confound phenotypic and genetic variation. We urge the use of a clear distinction between narrow‐sense Q_ST, which can be meaningfully compared with F_ST, and phenotypic divergence measured between populations, P_ST, which is inadequate for comparisons in the wild. We also point out that an unbiased estimate of Q_ST can be found using the so‐called ‘animal model’ of quantitative genetics.