Modeling temporal and spatial colony-site dynamics in a long-lived seabird

We studied the determinants of colony site dynamics in Audouin's gull, Larus audouinii, breeding in a small archipelago of the western Mediterranean. Data on island occupation were available for a series of 25 years, since first colonization of the archipelago in 1973. Group behavior was studied in relation to the components of dispersal: permanence or abandonment (extinction) on an island previously occupied and permanence or occupation (colonization) of another island. Generalized Linear Mixed Models (GLMMs) were used to identify the relative contribution of each explanatory variable to the probability of colony abandonment. Gulls showed a low probability (3%) of abandoning one of the islands (Grossa I.), especially when the colony was increasing in numbers from time t_i-1 to t_i. However, the probability of abandoning Grossa increased up to 31% when the colony was declining. The probability of island abandonment was very high for all other islands (range 66–99%) when the colony was declining, but much lower (range 36–82%) when it was increasing. Hence, we suggest that island abandonment by Audouin's gull is at least a two-step process. The first step (dispersal of a portion of the colony) probably takes place at random, as an evolutionary load typical of a species evolved in unstable habitats. The second step, a further loss of breeding pairs, seems to feedback on the first loss of members of the colony (public information), likely perceived as a loss of colony quality. Colonization of islands by gulls abandoning Grossa I. was marginally and negatively affected by the density of breeding yellow-legged gulls, a predatory species. Results apply to conservation ecology since they highlight the need to protect not only occupied patches but also those empty at present.     

Assessing plant-nutrient relationships in highly invaded Californian grasslands using non-normal probability distributions

Question: Is native species occurrence related to soil nutrients in highly invaded Californian annual grasslands? What is the best method to analyze this relationship, given that native species occur in very low numbers and are absent from many locations? Location: California, USA. Methods: We investigated the effects of soil characteristics and livestock grazing on native plant occurrence at 40 plots from six sites during the period 2003–2005. Low absolute cover (< 5.8%) of native species resulted in strongly skewed, zero-inflated data sets. To overcome problems in the analysis created by non-normality and correlations within plots, we used GLMs and GLMMs, either with a Poisson or a negative binomial distribution, to analyse native species richness and Nassella pulchra cover. Results: N. pulchra cover was strongly associated with low phosphorus in sandy soils, whereas native species richness was highest in soils with low available nitrogen (high C:N). Conclusion: Under current conditions, phosphorus seems to be a critical factor influencing abundance of N. pulchra. Low fertility soils may provide refugia for native species in highly invaded California grasslands as they may be below a threshold required for non-native annuals to completely dominate. By using non-normal distributions in linear models with random components, we report well fitted models with more accurately tested significant covariates.     

Relative male and female contributions to the supercooling point of their offspring in Microvelia reticulata (Heteroptera: Veliidae)

Cold hardiness is a key life history trait in temperate and polar ectothermic species, as it affects survival during overwintering, but its evolution is poorly understood. While many studies of cold hardiness in insects have shown differences between species, populations or developmental stages, data on the relative contribution of individual genotypes to cold hardiness are scarce and mainly limited to drosophilid fly species. We used a sib‐analysis (paternal half‐sib/full‐sib breeding design) to estimate the relative contributions of parental generation to the supercooling point (SCP) of the offspring of a heteropteran non‐model insect species, Microvelia reticulata (Heteroptera: Gerromorpha: Veliidae). We found that parent identity affected significantly SCP values of their offspring. Magnitudes of estimated sire and dam variance components were similar but the distributions of individual contributions to SCP differed between sires and dams, which points to sex‐specific genetic or parental effects on SCP in this species. The animal model failed to find a realistic estimate of heritability (h²) of SCP, suggesting that the underlying genetics of SCP in M. reticulata can not be characterized by purely additive effects.     

Female reproductive output in a Mediterranean shrub: effects from inflorescence to population

Inflorescence effects have been poorly studied, in spite of the functional relevance of the inflorescence in fruit and seed ecology. The present study focused on the effects of inflorescence size and phenology, and flower position within the inflorescence, in relation to fruit and seed production of the Mediterranean shrub Ononis fruticosa. Variability in fruit and seed production, seed weight and germination were estimated and modelled. Results confirmed that the most important predictors in seed production were inflorescence flowering time and flower position within the inflorescence. Thus, the number of mature seeds per fruit was higher in earlier inflorescences and in basal positions. On the other hand, predation was higher in fruits in basal positions. In fact, seed predation seemed to be the most important factor controlling final seed production. Models at the plant level suggested a negative incidence of geitonogamous pollination and resource limitation, which were also observed at the fruit level. This study confirmed the relevance of inflorescence effects on the reproductive output of O. fruticosa. Although the underlying processes could not be identified, our results provide several hypotheses for future experimental studies.     

Disentangling complex fine‐scale ecological patterns by path modelling using GLMM and GIS

Question: How can statistical modelling tools (GLMM) and GIS be used as an aid in understanding complex ecological patterns? This general question was approached by using bryophyte demography data as an example. More specifically, we asked what is the contribution of terrain shape to explaining the performance and fate of plant individuals, controlling for all other known relationships? Location: Norway. Methods: Information on demography was obtained for 140 populations of the perennial clonal bryophyte Hylocomium splendens in Norway spruce forests during an 11‐year period (1992‐2002). Performance (size and branching pattern) was recorded for mature segments and fate was recorded for growing points. Positions of each of the more than 30 000 recorded bryophyte ramets were coupled with (micro‐) topographic characteristics (slope and convexity) derived from fine‐scale digital elevation models in a GIS framework. Carefully planned sequences of generalised linear mixed models (GLMM) were performed to test predictions from a conceptual path model. Results: We demonstrate strong dependence of size on branching, fate and on vertical position in the bryophyte carpet, and an effect of vertical position on branching pattern. Micro‐topography contributed to explaining plant performance by four different mechanisms: (1) a direct effect of slope on the segment's vertical position in the carpet; (2‐3) direct effects of both slope and convexity on fates of individuals via controls on risk of burial; and (4) an indirect effect of convexity on branching pattern via a direct effect on size. No indication of a direct effect of terrain on branching was found. Conclusions: Our study exemplifies the usefulness of GLMM for disentangling complex ecological relationships. Specifically, we recognise micro‐topography as a potentially important factor for plant demography in general and for performance and fate of individuals in particular.     

Testing bespoke management of foraging habitat for European turtle doves Streptopelia turtur

Agri-environment schemes (AES) are increasingly being employed to mitigate biodiversity loss in agricultural environments. The European Turtle Dove Streptopelia turtur is an obligate granivorous bird in rapid decline within both the UK (−96% since 1970) and across continental Europe (−77% since 1980), despite widespread uptake of AES. Here, we assess the efficacy of a potentially new, sown agri-environment option designed to provide abundant, accessible seed for S. turtur during the breeding season. During summer 2011 we compared vegetation structure and seed provision on trial plots to control habitat types (existing agri-environment options thought to potentially provide S. turtur foraging habitat) to assess whether trial plots performed better for foraging S. turtur than control habitats. In September 2011 all trial plots were topped (cut) and half of a subset of trial plots were then scarified (60% of soil surface disturbed). Vegetation structure on topped, and topped and scarified trial plots was measured during summer 2012 to determine which management regime was most effective in maintaining suitable sward structure and seed provision into the second year. No control habitat type produced as much seed important in S. turtur diet as trial plots at any point during year one. Trial plots provided accessible vegetation structure early in the season with no difference in vegetation metrics between trial plots and previously published data on S. turtur foraging locations. However, to allow later access, management is required during mid-June to open up the sward through localized topping or scarification. Vegetation structure during year two was generally too dense to attract foraging S. turtur. However, scarifying trial plots during the September following sowing encouraged self-seeding of Fumaria. officinalis (a plant species historically forming a significant proportion of S. turtur diet during the breeding season) into the second year, with this species present in 16% of scarified trial plots compared to only 4% of topped trial plots during year two. Thus, autumn scarification, possibly followed by topping or scarification of part of the trial plots in June, is necessary for trial plots to provide more seed and access for S. turtur than existing agri-environment options during year two. We recommend modifications to our original seed mix in order to reduce vegetation density and improve vegetation structure. The study provides an example of the need to strike the right balance between food abundance and accessibility, through vegetation structure, when designing agri-environment scheme management options that provide food for birds.     

PROCEEDINGS of the 21st ANNUAL GENERAL MEETING of the SOUTH AFRICAN ORNITHOLOGICAL SOCIETY,HELD at the DEPARTMENT OF ZOOLOGY University of Cape Town,RONDEBOSCH, at 2.15 p.m., 9th DECEMBER, 1950

A fragmentary skull of a small passerine from the mid-Holocene organic-rich deposits at Florisbad, South Africa, shows a pattern of distinctive characters that allows its identification as a Cercomela chat. It resembles most closely the Familiar Chat C. familiaris and Karoo Chat C. schlegelii, which are still part of the avifauna in this part of South Africa. Furthermore, the significance of several characters of the skull for hypotheses on the phylogeny of Muscicapoidea in general, and Saxicolinae in particular, is discussed.     

干旱和林分因子对树木死亡的影响——以美国德克萨斯州东部国家森林为例

为探讨不同时间尺度、气候因子及林分因子对森林中树木死亡的影响,本研究以美国德克萨斯州东部的4个国家森林中264个重复调查的森林样地为对象,使用近20年来美国森林清查4个周期的数据,估算其在清查周期和年度水平上的树木死亡率变化,并使用广义线性混合效应模型来分析气候因子(干旱强度、干旱持续时间、年均温和年降水量)、树木大小(胸径)和林分因子(树木胸高断面积、林分密度和林分年龄)对树木存活的影响。结果表明: 在重度干旱当年和重度干旱的清查周期中,森林的树木死亡率分别增加了151%和123%,天气干扰(干旱和飓风)和植物之间的竞争是其主要的影响因素;干旱强度(标准化降水蒸散发指数,SPEI)和干旱持续时间对树木的存活具有显著的负效应,年降水量对树木的存活具有显著的正效应;树木胸高面积对树木存活具有显著的负效应,树木大小、林分年龄和林分密度对树木存活均具有显著的正效应,但是大树比小树更容易受到天气影响而死亡;在重度干旱的清查周期中,松树种组的树木死亡率(2.1%)比阔叶树木种组(3.9%)低,天然林的树木死亡率(3.0%)高于人工林(1.9%)。在分析树木死亡率时,需同时考虑个体树木大小、林分因子与气候因子的相对重要性。     

Improving population estimates by quantifying diving and surfacing patterns: A dugong example

Diving animals are available for detection from above the water when environmental conditions are favorable and the animals are near the surface. The number of animals that are unavailable for detection needs to be estimated to obtain unbiased population estimates. The current availability correction factors used in aerial surveys for the dugong (Dugong dugon) allow for variation in environmental conditions but use the average time dugongs spend near the surface (i.e., constant availability corrections). To improve availability estimates, we examined location and dive data from nine dugongs fitted with satellite telemetry units and time‐depth recorders (TDRs) in eastern Australia. The effects of water depth, tidal conditions, and habitat types on dugong surfacing time were examined using generalized linear mixed models (GLMMs). We found that availability for detection differed with water depth, and depth‐specific availability estimates were often lower than the constant estimates. The habitat effect was less influential, and there was no tidal effect. The number of dugongs estimated using depth‐specific availabilities were higher than those obtained using constant availabilities across water depth. Hence, information on water depth can refine availability estimates and subsequent abundance estimates from dugong aerial surveys. The methodology may be applicable to other aquatic wildlife.