https://science.sciencemag.org/content/sci/197/4300/215.full.pdf

Ecology, sexual selection, and the evolution of mating systems

Both the magnitude and the urgency of the task of assessing global biodiversity require that we make the most of what we know through the use of estimation and extrapolation. Likewise, future biodiversity inventories need to be designed around the use of effective sampling and estimation procedures, especially for 'hyperdiverse' groups of terrestrial organisms, such as arthropods, nematodes, fungi, and microorganisms. The challenge of estimating patterns of species richness from samples can be separated into (i) the problem of estimating local species richness, and (ii) the problem of estimating the distinctness, or complementarity, of species assemblages. These concepts apply on a wide range of spatial, temporal, and functional scales. Local richness can be estimated by extrapolating species accumulation curves, fitting parametric distributions of relative abundance, or using non-parametric techniques based on the distribution of individuals among species or of species among samples. We present several of these methods and examine their effectiveness for an example data set. We present a simple measure of complementarity, with some biogeographic examples, and outline the difficult problem of estimating complementarity from samples. Finally, we discuss the importance of using 'reference' sites (or sub-sites) to assess the true richness and composition of species assemblages, to measure ecologically significant ratios between unrelated taxa, to measure taxon/sub-taxon (hierarchical) ratios, and to 'calibrate' standardized sampling methods. This information can then be applied to the rapid, approximate assessment of species richness and faunal or floral composition at 'comparative' sites.

Estimating Terrestrial Biodiversity through Extrapolation

SUMMARY
1According to ‘Gause's hypothesis’ a corollary of the process of evolution by natural selection is that in a community at equilibrium every species must occupy a different niche. Many botanists have found this idea improbable because they have ignored the processes of regeneration in plant communities.
2Most plant communities are longer-lived than their constituent individual plants. When an individual dies, it may or may not be replaced by an individual of the same species. It is this replacement stage which is all-important to the argument presented.
3Several mechanisms not involving regeneration also contribute to the maintenance of species-richness:


(a). differences in life-form coupled with the inability of larger plants to exhaust or cut off all resources, also the development of dependence-relationships,
(b) differences in phenology coupled with tolerance of suppression,
(c) fluctuations in the environment coupled with relatively small differences in competitive ability between many species,
(d) the ability of certain species-pairs to form stable mixtures because of a balance of intraspecific competition against interspecific competition,
(e) the production of substances more toxic to the producer-species than to the other species,
(f) differences in the primary limiting mineral nutrients or pore-sizes in the soil for neighbouring plants of different soecies, and
(g) differences in the competitive abilities of species dependent on their physiological age coupled with the uneven-age structure of many populations.


4The mechanisms listed above do not go far to explain the indefinite persistence in mixture of the many species in the most species-rich communities known.
5In contrast there seem to be almost limitless possibilities for differences between species in their requirements for regeneration, i.e. the replacement of the individual plants of one generation by those of the next. This idea is illustrated for tree species and it is emphasized that foresters were the first by a wide margin to appreciate its importance.
6The processes involved in the successful invasion of a gap by a given plant species and some characters of the gap that may be important are summarized in Table 2.
7The definition of a plant's niche requires recognition of four components:


(a) the habitat niche,
(b) the life-form niche,
(c) the phenological niche, and
(d) the regeneration niche.


8A brief account is given of the patterns of regeneration in different kinds of plant community to provide a background for studies of differentiation in the regeneration niche.
9All stages in the regeneration-cycle are potentially important and examples of differentiation between species are given for each of the following stages:


(a) Production of viable seed (including the sub-stages of flowering, pollination and seed-set),
(b) dispersal, in space and time,
(c) germination,
(d) establishment, and
(e) further development of the immature plant.


10In the concluding discussion emphasis is placed on the following themes:


(a) the kinds of work needed in future to prove or disprove that differentiation in the regeneration niche is the major explanation of the maintenance of species-richness in plant communities,
(b) the relation of the present thesis to published ideas on the origin of phenological spread,
(c) the relevance of the present thesis to the discussion on the presence of continua in vegetation,
(d) the co-incidence of the present thesis and the emerging ideas of evolutionists about differentiation of angiosperm taxa, and
(e) the importance of regeneration-studies for conservation.

The maintenance of species-richness in plant communities: the importance of the regeneration niche

Food webs in nature have multiple, reticulate connections between a diversity of consumers and resources. Such complexity affects web dynamics: it first spreads the direct effects of consumption and productivity throughout the web rather than focusing them at particular "trophic levels." Second, consumer densities are often donor controlled with food from across the trophic spectrum, the herbivore and detrital channels, other habitats, life-history omnivory, and even trophic mutualism. Although consumers usually do not affect these resources, increased numbers often allow consumers to depress other resources to levels lower than if donor-controlled resources were absent. We propose that such donor-controlled and "multichannel" omnivory is a general feature of consumer control and central to food web dynamics. This observation is contrary to the normal practice of inferring dynamics by simplifying webs into a few linear "trophic levels," as per "green world" theories. Such theories do not accommodate commo...

Food Web Complexity and Community Dynamics

The use of recommender systems is an emerging trend today, when user behavior information is abundant. There are many large datasets available for analysis because many businesses are interested in future user opinions. Sophisticated algorithms that predict such opinions can simplify decision-making, improve customer satisfaction, and increase sales. However, modern datasets contain millions of records, which represent only a small fraction of all possible data. Furthermore, much of the information in such sparse datasets may be considered irrelevant for making individual recommendations. As a result, there is a demand for a way to make personalized suggestions from large amounts of noisy data.
Current recommender systems are usually all-in-one applications that provide one type of recommendation. Their inflexible architectures prevent detailed examination of recommendation accuracy and its causes. We introduce a novel architecture model that supports scalable, distributed suggestions from multiple independent nodes. Our model consists of two components, the input matrix generation algorithm and multiple platform-independent combination algorithms. A dedicated input generation component provides the necessary data for combination algorithms, reduces their size, and eliminates redundant data processing. Likewise, simple combination algorithms can produce recommendations from the same input, so we can more easily distinguish between the benefits of a particular combination algorithm and the quality of the data it receives. Such flexible architecture is more conducive for a comprehensive examination of our system.
We believe that a user's future opinion may be inferred from a small amount of data, provided that this data is most relevant. We propose a novel algorithm that generates a more optimal recommender input. Unlike existing approaches, our method sorts the relevant data twice. Doing this is slower, but the quality of the resulting input is considerably better. Furthermore, the modular nature of our approach may improve its performance, especially in the cloud computing context. We implement and validate our proposed model via mathematical modeling, by appealing to statistical theories, and through extensive experiments, data analysis, and empirical studies.
Our empirical study examines the effectiveness of accuracy improvement techniques for collaborative filtering recommender systems. We evaluate our proposed architecture model on the Netflix dataset, a popular (over 130,000 solutions), large (over 100,000,000 records), and extremely sparse (1.1%) collection of movie ratings. The results show that combination algorithm tuning has little effect on recommendation accuracy. However, all algorithms produce better results when supplied with a more relevant input. Our input generation algorithm is the reason for a considerable accuracy improvement.

/pdf/a-distributed-architecture-centric-approach-to-computing-31zmh6iinx.pdf

A distributed, architecture-centric approach to computing accurate recommendations from very large and sparse datasets

Costa Rica hosts an avifauna of more than 830 species. Within two hours drive from San Jose, one can see quetzals in highland forests, antbirds in lowland forests, or shorebirds and ibises in mangrove swamps. The authors describe the landforms, vegetation and climates of Costa Rica and include photographs of some of the major types of habitat and characteristic plants. They discuss some aspects of evolution, ecology, and behaviour of Costa Rican birds, and report on the costly and courageous conservation efforts the country is making. The family and species accounts which follow, covering some 400 pages, make up the bulk of the book, with 52 colour plates illustrating virtually every species of Costa Rican bird-migrants as well as residents - including distinctive plumages for many of them. There are also practical tips for trips in the field and descriptions of good birding locations, with specific directions for travel by car, public transport and on foot.

A Guide to the Birds of Costa Rica

Nine hummingbird—pollinated species of Heliconia occur together at Finca La Selva, in the wet Caribbean lowlands of Costa Rica. In forest habitats, Heliconia clumps (clones) are typically small; in more open areas, many clumps attain large size. This probably reflects differences in light intensity and degree of vegetative competition in these habitats. Nine species of hummingbirds regularly visit Heliconia flowers at La Selva. The four hermits are nonterritorial, traplining foragers with long, curved bills. Non—hermits frequently hold territories at Heliconia clumps, and have short, straight bills. Pollination by hermits tends to produce more cross—pollination; territorial hummingbirds increase self—pollination. Different Heliconia species appear to be specialized for pollination by either hermits on non—hermits, largely through components of the caloric phenotype: amount and timing of nectar production, rate of inflorescene and flower production, and morphological paramerters that affect the energetic efficiency of nectar—harvesting hummingbirds. Habitat may influence pollination systems through its effects on clump size and thus on the number of flowers a clump can have at any one time. Ultimately, specialization for hermits or non—hermits may depend on the degree of self—compatibility of the different Heliconia species. Hermit—pollinated Heliconia mostly show sequential and nonoverlapping flowering peaks, probably resulting from competition for pollinators and/or selection against hybridization. Two hermit—pollinated species bloom simultanesoulsy, thereby inducing the birds to utilize an other—wise little—used microhabitat. Heliconia species pollinated by non—hermits bloom in the early to middle rainy season, and are mostly separated by habitat. Isolating mechanisms among sympatric Heliconia species involve both spatial and temporal patterns of partioning available pollinators. Floral parameters include mechanical (different site of pollen deposition on the bird) and ethological (caloric and visual factors affecting flower choice) mechanisms. Selection for pollinator specificity may result in convergence of blooming peaks, provided that other isolating mechanisms are present. Human activity has broken down some habitat barriers by producing large areas of second growth.

Ecology, Flowering Phenology, and Hummingbird Pollination of Some Costa Rican Heliconia Species

Seasonal movements are common in Neotropical forest birds. Species that engage in the largest movements, altitudinal and intratropical migrants, are predominantly frugivores or nectarivores of canopy/edge or dry habitats. Migration by such species may be necessitated by the high spatial and temporal variation in their resource base. We hypothesize that seasonal movements within the tropics predisposed these birds to migration out of the tropics. Indeed, most Nearctic passerine migrants are drawn from Neotropical taxa that exhibit altitudinal or intratropical migration. Conversely, taxa comprising the most sedentary group of Neotropical residents (understory insectivores) are poorly represented among Nearctic migrants. Further evidence of an evolutionary link between seasonal movements within the tropics and long-distance migration is provided by similarities in habitat use and diet between overwintering Nearctic migrants and closely related tropical residents. Both groups tend to be frugivorous/nectarivor...

https://www.jstor.org/stable/pdfplus/2462776.pdf

Evolutionary Precursors of Long-Distance Migration: Resource Availability and Movement Patterns in Neotropical Landbirds

Ecological Organization of a Tropical, Highland Hummingbird Community

The overall objective is to compare the ecological impact of bird-flower coevolution in different geographical areas. However, it is first necessary to define the parameters of such coevolution in broader terms than those of the traditional "syndrome of ornithophily," which focuses very narrowly on some aspects of floral morphology. I recognize three distinct components of flower function: attraction, reward, and filtering mechanisms, and discuss their functioning in an ecological context, and as they relate to the genetic system or "pollination unit" of the plant. Then I turn to nectarfeeding birds, and discuss not only morphological, but ecological and behavioral specializations to flowers as a food source. These discussions develop explicitly my criteria for detecting and evaluating bird-flower coevolution. The different groups of birds known to feed regularly (as opposed to opportunistically) on nectar are then compared according to these criteria, to determine their relative degrees of specialization for, and dependence upon, a high-nectar diet. Different groups are found to vary widely in their degrees of specialization for flower-feeding, and it is evident that bird-flower coevolution has followed very different courses, and led to widely divergent ecological systems in different geographical areas. By any criteria the hummingbirds are the most specialized avian nectarivores, although they are approached in this regard by some members of certain passerine groups, notably among the sunbirds. Several groups of passerine nectarivores also occur with the hummingbirds in many New World areas; these groups show low to moderate degrees of specialization for nectarivory, either as pollinators or as parasites on the hummingbird-flower system. The New World tropics thus present a wide range of specializations for flower-feeding in their avifauna, and represent a particularly interesting area for study. Patterns of ornithophily and nectarivory are thus examined in detail for this area, concentrating specifically on Southern Central America, especially Costa Rica. The altitudinal and geographical distributions of the two main groups of hummingbirds, the hermits and nonhermits, are found to differ, as are the taxonomic and ecological affinities of their primary foodplants. The hermits are most numerous in wet lowlands and the adjacent foothills, and are primarily associated with large monocotyledonous herbs, notably Heliconia. The nonhermits reach their greatest taxonomic and ecological diversity in the lower middle elevations, and are the only group present at high elevations; they seem to have coevolved with the flowers of a variety of dicot families, and the bromeliads among the monocots. Passerine nectarivores occur primarily as parasites on the hummingbird-flower system (Coerebidae) and are important as pollinators only in seasonally dry areas when the hummingbirds are poorly represented.

F. Gary Stiles

Papers

A Guide to the Birds of Costa Rica

Ecology, Flowering Phenology, and Hummingbird Pollination of Some Costa Rican Heliconia Species

Evolutionary Precursors of Long-Distance Migration: Resource Availability and Movement Patterns in Neotropical Landbirds

Ecological Organization of a Tropical, Highland Hummingbird Community

Geographical aspects of bird-flower coevolution, with particular reference to central america'