Ecological studies of the surface microlayer of small ponds at the UWM Field Station

The seasonal variation and enrichment of nutrients, pigments, bacteria, fungi and algae in the surface microlayer and subsurface waters were investigated in three ponds at the University of Wisconsin-Milwaukee Field Station, Saukville, Ozaukee County, Wisconsin. Samples were collected intermittently from June, 1978 through October, 1981. Microlayer samples were collected using a glass plate and a screen sampler. All ponds showed dramatic seasonal variations in nutrients, microorganisms and algae in both surface and subsurface waters. The data indicate that physical factors such as adsubble processes, antirain and atmospheric deposition, along with biological factors such as heterotrophic mineralization and autotrophic uptake, play significant roles in causing the enrichment or lack of enrichment of materials within the microlayer. Furthermore, this study suggests that surface microlayers, particularly in shallow environments where algal species are adapted to high light conditions. can be sites of high biological activity

TRiP: Tracking Rhythms in Plants, an Automated Leaf Movement Analysis Program for Circadian Period Estimation

Background: A well characterized output of the circadian clock in plants is the daily rhythmic movement of leaves. This process has been used extensively in Arabidopsis to estimate circadian period in natural accessions as well as mutants with known defects in circadian clock function. Current methods for estimating circadian period by leaf movement involve manual steps throughout the analysis and are often limited to analyzing one leaf or cotyledon at a time. Methods: In this study, we describe the development of TRiP (Tracking Rhythms in Plants), a new method for estimating circadian period using a motion estimation algorithm that can be applied to whole plant images. To validate this new method, we apply TRiP to a Recombinant Inbred Line (RIL) population in Arabidopsis using our high-throughput imaging platform. We begin imaging at the cotyledon stage and image through the emergence of true leaves. TRiP successfully tracks the movement of cotyledons and leaves without the need to select individual leaves to be analyzed

Age and terminal reproductive attempt influence laying date in the Thorn‐tailed Rayadito

Age‐specific variation in reproductive effort can affect population dynamics, and is a key component of the evolution of reproductive tactics. Late‐life declines are a typical feature of variation in reproduction. However, the cause of these declines, and thus their implications for the evolution of life‐history tactics, may differ. Some prior studies have shown late‐life reproductive declines to be tied to chronological age, whereas other studies have found declines associated with terminal reproduction irrespective of chronological age. We investigated the extent to which declines in late life reproduction are related to chronological age, terminal reproductive attempt or a combination of both in the Thorn‐tailed Rayadito (Aphrastura spinicauda), a small passerine bird that inhabits the temperate forest of South America. To this end we used long‐term data (10 years) obtained on reproductive success (laying date, clutch size and nestling weight) of females in a Chilean population. Neither chronological age nor terminal reproductive attempt explained variation in clutch size or nestling weight, however we observed that during the terminal reproductive attempt older females tended to lay later in the breeding season and younger females laid early in the breeding season, but this was not the case when the reproductive attempt was not the last. These results suggests that both age‐dependent and age‐independent effects influence reproductive output and therefore that the combined effects of age and physiological condition may be more relevant than previously thought

Molecular Phylogenetics and the Diversification of Hummingbirds

SummaryThe tempo of species diversification in large clades can reveal fundamental evolutionary mechanisms that operate on large temporal and spatial scales [1–4]. Hummingbirds have radiated into a diverse assemblage of specialized nectarivores comprising 338 species, but their evolutionary history has not, until now, been comprehensively explored. We studied hummingbird diversification by estimating a time-calibrated phylogeny for 284 hummingbird species, demonstrating that hummingbirds invaded South America by ∼22 million years ago, and subsequently diversified into nine principal clades (see [5–7]). Using ancestral state reconstruction and diversification analyses, we (1) estimate the age of the crown-group hummingbird assemblage, (2) investigate the timing and patterns of lineage accumulation for hummingbirds overall and regionally, and (3) evaluate the role of Andean uplift in hummingbird speciation. Detailed analyses reveal disparate clade-specific processes that allowed for ongoing species diversification. One factor was significant variation among clades in diversification rates. For example, the nine principal clades of hummingbirds exhibit ∼15-fold variation in net diversification rates, with evidence for accelerated speciation of a clade that includes the Bee, Emerald, and Mountain Gem groups of hummingbirds. A second factor was colonization of key geographic regions, which opened up new ecological niches. For example, some clades diversified in the context of the uplift of the Andes Mountains, whereas others were affected by the formation of the Panamanian land bridge. Finally, although species accumulation is slowing in all groups of hummingbirds, several major clades maintain rapid rates of diversification on par with classical examples of rapid adaptive radiation

Exploratory behavior, but not aggressiveness, is correlated with breeding dispersal propensity in the highly philopatric thorn-tailed rayadito

Studies on the relationship between behavioral traits and dispersal are necessary to understand the evolution of dispersal syndromes. Empirical studies have mainly focused on natal dispersal, even though behavioral differences between dispersers and philopatric individuals are suspected to hold through the whole life cycle, potentially affecting breeding dispersal propensity. Using capture–mark–recapture data and behavioral trials in a forest passerine, the thorn-tailed rayadito Aphrastura spinicauda, we describe inter-individual differences in exploratory behavior and aggressiveness, and investigate the relationship between those traits and breeding dispersal. Our study took place in Fray Jorge National Park, north-central Chile, where a relatively isolated population of rayaditos inhabits a naturally fragmented environment. We found that scores for behavioral traits were consistent between years. Exploratory behavior was similar between sexes, while males showed higher levels of aggression towards a conspecific male intruder. Only exploratory behavior was related to breeding dispersal propensity, with fast-exploring rayaditos being more likely to have dispersed between seasons. This finding provides indirect evidence for the existence of a dispersal strategy that could reduce dispersal costs in the fragmented landscape of Fray Jorge. To our knowledge, this is the first study documenting an association between breeding dispersal and exploratory behavior in a wild bird population. A longitudinal individual-based study will help determining whether this association constitutes a behavioral syndrome.Indexación: Scopu

Food abundance does not determine bird use of early-successional habitat.

Abstract. Few attempts have been made to experimentally address the extent to which temporal or spatial variation in food availability influences avian habitat use. We used an experimental approach to investigate whether bird use differed between treated (arthropods reduced through insecticide application) and control (untreated) forest canopy gaps within a bottomland hardwood forest in the Upper Coastal Plain of South Carolina, USA. Gaps were two- to three-year-old group selection timber harvest openings of three sizes (0.13, 0.26, and 0.50 ha). Our study was conducted during four bird use periods (spring migration, breeding, post-breeding, and fall migration) in 2002 and 2003. Arthropods were reduced in treated gaps by 68% in 2002 and 73% in 2003. We used mist-netting captures and foraging attack rates to assess the influence of arthropod abundance on avian habitat use. Evidence that birds responded to arthropod abundance was limited and inconsistent. In 2002, we generally captured more birds in treated gaps of the smallest size (0.13 ha) and fewer birds in treated gaps of the larger sizes. In 2003, we recorded few differences in the number of captures in treated and control gaps. Foraging attack rates generally were lower in treated than in control gaps, indicating that birds were able to adapt to the reduced food availability and remain in treated gaps. We conclude that arthropod abundance was not a proximate factor controlling whether forest birds used our gaps. The abundance of food resources may not be as important in determining avian habitat selection as previous research has indicated, at least for passerines in temperate subtropical regions