University of California, Santa Barbara

About: University of California, Santa Barbara is a education organization based out in Santa Barbara, California, United States. It is known for research contribution in the topics: Population & Galaxy. The organization has 30281 authors who have published 80852 publications receiving 4626827 citations. The organization is also known as: UC Santa Barbara & UCSB.

A niche for neutrality.

Abstract: Ecologists now recognize that controversy over the relative importance of niches and neutrality cannot be resolved by analyzing species abundance patterns. Here, we use classical coexistence theory to reframe the debate in terms of stabilizing mechanisms (niches) and fitness equivalence (neutrality). The neutral model is a special case where stabilizing mechanisms are absent and species have equivalent fitness. Instead of asking whether niches or neutral processes structure communities, we advocate determining the degree to which observed diversity reflects strong stabilizing mechanisms overcoming large fitness differences or weak stabilization operating on species of similar fitness. To answer this question, we propose combining data on per capita growth rates with models to: (i) quantify the strength of stabilizing processes; (ii) quantify fitness inequality and compare it with stabilization; and (iii) manipulate frequency dependence in growth to test the consequences of stabilization and fitness equivalence for coexistence.

Carbon-based ocean productivity and phytoplankton physiology from space

Abstract: carbon(C)andchlorophyll(Chl)biomassandshowthatderivedChl:Cratioscloselyfollow anticipated physiological dependencies on light, nutrients, and temperature. With this new information, global estimates of phytoplankton growth rates (m) and carbon-based NPP are made for the first time. Compared to an earlier chlorophyll-based approach, our carbonbased values are considerably higher in tropical oceans, show greater seasonality at middle and high latitudes, and illustrate important differences in the formation and demise of regional algal blooms. This fusion of emerging concepts from the phycological and remote sensing disciplines has the potential to fundamentally change how we model and observe carbon cycling in the global oceans.

Propagule dispersal in marine and terrestrial environments: a community perspective

Abstract: Studies in terrestrial systems suggest that long-distance propagule dispersal is important for landscape pattern and dynamics, but largely inconsequential for local demography. By contrast, in marine systems, dispersal at regional scales may drive local dynamics, because many species may have large mean dispersal distances. To assess var- iation in marine dispersal scales, we estimated mean dispersal distances from genetic iso- lation-by-distance slopes. Estimates ranged widely, from a few meters to hundreds of kilometers. Dispersal differed among taxonomic groups (macroalgae, invertebrates, and fish) and among species in different functional groups (e.g., producers and herbivores). Differences in dispersal scale have important implications for marine community dynamics, reserve design, responses to large-scale perturbations, and evolution of interacting species. To place genetic estimates of marine dispersal in context, we compared them to other measures of dispersal in the ocean and to estimates of dispersal on land. Maximum scales of dispersal by sedentary marine species exceeded maximum estimates of terrestrial plant dispersal by at least one to two orders of magnitude. Direct and genetic estimates of terrestrial plant dispersal were comparable to estimates of marine plant dispersal. Rates of marine macroalgal range expansion, however, far exceeded spread rates of terrestrial plants. Terrestrial plant spread rates were more similar to those of short-dispersing marine organ- isms that lack secondary dispersal by drifting adults. Genetic estimates of dispersal by different functional groups suggest that herbivores typically disperse much farther than their plant resources both on land and in the sea, although the timing, frequency, and consequences of dispersal may differ in the two systems. Terrestrial herbivores have more flexible dispersal behavior than marine organisms that disperse each generation by plank- tonic transport of larvae. Our results validate some long-standing views about the greater dispersal potential of species in the ocean, but also highlight the extreme heterogeneity in dispersal scale among marine species. As a result, development of a community perspective on marine connectivity will require consideration of multiple dispersal mechanisms and scales.

Ozone depletion: ultraviolet radiation and phytoplankton biology in antarctic waters.

Abstract: The springtime stratospheric ozone (O3) layer over the Antarctic is thinning by as much as 50 percent, resulting in increased midultraviolet (UVB) radiation reaching the surface of the Southern Ocean. There is concern that phytoplankton communities confined to near-surface waters of the marginal ice zone will be harmed by increased UVB irradiance penetrating the ocean surface, thereby altering the dynamics of Antarctic marine ecosystems. Results from a 6-week cruise (Icecolors) in the marginal ice zone of the Bellingshausen Sea in austral spring of 1990 indicated that as the O3 layer thinned: (i) sea surface- and depth-dependent ratios of UVB irradiance (280 to 320 nanometers) to total irradiance (280 to 700 nanometers) increased and (ii) UVB inhibition of photosynthesis increased. These and other Icecolors findings suggest that O3-dependent shifts of in-water spectral irradiances alter the balance of spectrally dependent phytoplankton processes, including photoinhibition, photoreactivation, photoprotection, and photosynthesis. A minimum 6 to 12 percent reduction in primary production associated with O3 depletion was estimated for the duration of the cruise.

First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole

Abstract: We present the first Event Horizon Telescope (EHT) images of M87, using observations from April 2017 at 1.3 mm wavelength. These images show a prominent ring with a diameter of ~40 μas, consistent with the size and shape of the lensed photon orbit encircling the "shadow" of a supermassive black hole. The ring is persistent across four observing nights and shows enhanced brightness in the south. To assess the reliability of these results, we implemented a two-stage imaging procedure. In the first stage, four teams, each blind to the others' work, produced images of M87 using both an established method (CLEAN) and a newer technique (regularized maximum likelihood). This stage allowed us to avoid shared human bias and to assess common features among independent reconstructions. In the second stage, we reconstructed synthetic data from a large survey of imaging parameters and then compared the results with the corresponding ground truth images. This stage allowed us to select parameters objectively to use when reconstructing images of M87. Across all tests in both stages, the ring diameter and asymmetry remained stable, insensitive to the choice of imaging technique. We describe the EHT imaging procedures, the primary image features in M87, and the dependence of these features on imaging assumptions.