Conservationists are far from able to assist all species under threat, if only for lack of funding. This places a premium on priorities: how can we support the most species at the least cost? One way is to identify 'biodiversity hotspots' where exceptional concentrations of endemic species are undergoing exceptional loss of habitat. As many as 44% of all species of vascular plants and 35% of all species in four vertebrate groups are confined to 25 hotspots comprising only 1.4% of the land surface of the Earth. This opens the way for a 'silver bullet' strategy on the part of conservation planners, focusing on these hotspots in proportion to their share of the world's species at risk.

Biodiversity hotspots for conservation priorities

The extent of our reliance on animal pollination for world crop production for human food has not previously been evaluated and the previous estimates for countries or continents have seldom used primary data. In this review, we expand the previous estimates using novel primary data from 200 countries and found that fruit, vegetable or seed production from 87 of the leading global food crops is dependent upon animal pollination, while 28 crops do not rely upon animal pollination. However, global production volumes give a contrasting perspective, since 60% of global production comes from crops that do not depend on animal pollination, 35% from crops that depend on pollinators, and 5% are unevaluated. Using all crops traded on the world market and setting aside crops that are solely passively self-pollinated, wind-pollinated or parthenocarpic, we then evaluated the level of dependence on animal-mediated pollination for crops that are directly consumed by humans. We found that pollinators are essential for 13 crops, production is highly pollinator dependent for 30, moderately for 27, slightly for 21, unimportant for 7, and is of unknown significance for the remaining 9. We further evaluated whether local and landscape-wide management for natural pollination services could help to sustain crop diversity and production. Case studies for nine crops on four continents revealed that agricultural intensification jeopardizes wild bee communities and their stabilizing effect on pollination services at the landscape scale.

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Importance of pollinators in changing landscapes for world crops

. Much confusion exists in the English-language literature on plant invasions concerning the terms ‘naturalized’ and ‘invasive’ and their associated concepts. Several authors have used these terms in proposing schemes for conceptualizing the sequence of events from introduction to invasion, but often imprecisely, erroneously or in contradictory ways. This greatly complicates the formulation of robust generalizations in invasion ecology.

Based on an extensive and critical survey of the literature we defined a minimum set of key terms related to a graphic scheme which conceptualizes the naturalization/invasion process. Introduction means that the plant (or its propagule) has been transported by humans across a major geographical barrier. Naturalization starts when abiotic and biotic barriers to survival are surmounted and when various barriers to regular reproduction are overcome. Invasion further requires that introduced plants produce reproductive offspring in areas distant from sites of introduction (approximate scales: > 100 m over  6 m/3 years for taxa spreading by roots, rhizomes, stolons or creeping stems). Taxa that can cope with the abiotic environment and biota in the general area may invade disturbed, seminatural communities. Invasion of successionally mature, undisturbed communities usually requires that the alien taxon overcomes a different category of barriers.

We propose that the term ‘invasive’ should be used without any inference to environmental or economic impact. Terms like ‘pests’ and ‘weeds’ are suitable labels for the 50–80% of invaders that have harmful effects. About 10% of invasive plants that change the character, condition, form, or nature of ecosystems over substantial areas may be termed ‘transformers’.

/pdf/naturalization-and-invasion-of-alien-plants-concepts-and-43idu8swf7.pdf

Naturalization and invasion of alien plants: concepts and definitions

Beginning with Emlen (1966) and MacArthur and Pianka (1966) and extending through the last ten years, several authors have sought to predict the foraging behavior of animals by means of mathematical models. These models are very similar,in that they all assume that the fitness of a foraging animal is a function of the efficiency of foraging measured in terms of some "currency" (Schoener, 1971) -usually energy- and that natural selection has resulted in animals that forage so as to maximize this fitness. As a result of these similarities, the models have become known as "optimal foraging models"; and the theory that embodies them, "optimal foraging theory." The situations to which optimal foraging theory has been applied, with the exception of a few recent studies, can be divided into the following four categories: (1) choice by an animal of which food types to eat (i.e., optimal diet); (2) choice of which patch type to feed in (i.e., optimal patch choice); (3) optimal allocation of time to different patches; and (4) optimal patterns and speed of movements. In this review we discuss each of these categories separately, dealing with both the theoretical developments and the data that permit tests of the predictions. The review is selective in the sense that we emphasize studies that either develop testable predictions or that attempt to test predictions in a precise quantitative manner. We also discuss what we see to be some of the future developments in the area of optimal foraging theory and how this theory can be related to other areas of biology. Our general conclusion is that the simple models so far formulated are supported are supported reasonably well by available data and that we are optimistic about the value both now and in the future of optimal foraging theory. We argue, however, that these simple models will requre much modification, espicially to deal with situations that either cannot easily be put into one or another of the above four categories or entail currencies more complicated that just energy.

Citation classic - optimal foraging - a selective review of theory and tests

With a simple model, I show that comparisons of invasibility between regions are impossible to make unless one can control for all of the variables besides invasibility that influence exotic richness, including the rates of immigration of species and the characteristics of the invading species themselves. Using data from the literature for 184 sites around the world, I found that nature reserves had one-half of the exotic fraction of sites outside reserves, and island sites had nearly three times the exotic fraction of mainland sites. However, the exotic fraction and the number of exotics were also dependent on site area, and this had to be taken into account to make valid comparisons between sites. The number of native species was used as a surrogate for site area and habitat diversity. Nearly 70% of the variation in the number of exotic species was accounted for by a multiple regression containing the following predictors: the number of native species, whether the site was an island or on the mainland, and whether or not it was a nature reserve.

After controlling for scale, there were significant differences among biomes, but not continents, in their level of invasion. Multiple biome regions and temperate agricultural or urban sites were among the most invaded biomes, and deserts and savannas were among the least. However, there was considerable within-group variation in the mean degree of invasion. Scale-controlled analysis also showed that the New World is significantly more invaded than the Old World, but only when site native richness (probably a surrogate for habitat diversity) is factored out. Contrary to expectation, communities richer in native species had more, not fewer, exotics. For mainland sites, the degree of invasion increased with latitude, but there was no such relationship for islands. Although islands are more invaded than mainland sites, this is apparently not because of low native species richness, as the islands in this data set were no less rich in native species than were mainland sites of similar area. The number of exotic species in nature reserves increases with the number of visitors. However, it is difficult to draw conclusions about relative invasibility, invasion potential, or the roles of dispersal and disturbance from any of these results. Most of the observed patterns here and in the literature could potentially be explained by differences between regions in species properties, ecosystem properties, or propagule pressure.

Global patterns of plant invasions and the concept of invasibility

Functional floral phenology and morphology breeding systems pollen and stigma biology advertisements in flowers rewards in flowers the plant-pollinator interface abiotic pollination.

Pollination ecology: a practical approach.

Pollinators provide essential ecosystem services, and declines in some pollinator communities around the world have been reported. Understanding the fundamental components defining these communities is essential if conservation and restoration are to be successful. We examined the structure of plant-pollinator communities in a dynamic Mediterranean landscape, comprising a mosaic of post-fire regenerating habitats, and which is a recognized global hotspot for bee diversity. Each community was characterized by a highly skewed species abundance distribution, with a few dominant and many rare bee species, and was consistent with a log series model indicating that a few environmental factors govern the community. Floral community composition, the quantity and quality of forage resources present, and the geographic locality organized bee communities at various levels: (1) The overall structure of the bee community (116 species), as revealed through ordination, was dependent upon nectar resource diversity (defined as the variety of nectar volume-concentration combinations available), the ratio of pollen to nectar energy, floral diversity, floral abundance, and post-fire age. (2) Bee diversity, measured as species richness, was closely linked to floral diversity (especially of annuals), nectar resource diversity, and post-fire age of the habitat. (3) The abundance of the most common species was primarily related to post-fire age, grazing intensity, and nesting substrate availability. Ordination models based on age-characteristic post-fire floral community structure explained 39-50% of overall variation observed in bee community structure. Cluster analysis showed that all the communities shared a high degree of similarity in their species composition (27-59%); however, the geographical location of sites also contributed a smaller but significant component to bee community structure. We conclude that floral resources act in specific and previously unexplored ways to modulate the diversity of the local geographic species pool, with specific disturbance factors, superimposed upon these patterns, mainly affecting the dominant species.

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Linking bees and flowers: how do floral communities structure pollinator communities?

Practical Pollination Biology

Many flowers produce rewards, usually nectar or pollen or both. C. K. Sprengel (165), the founder of modern floral biology, was the first to report that flowers do not always reward pollinators; his observations were on the genus Orchis. Subsequent authors (7; 51; 66; 97; 99; 105; 186, p. 21; 195) have discussed various aspects of deceitful flowers that attract pollinators by resembling rewarding flowers or other objects.

Mimicry and Deception in Pollination

1. The habitat components determining the structure of bee communities are well known when considering foraging resources; however, there is little data with respect to the role of nesting resources. 2. As a model system this study uses 21 diverse bee communities in a Mediterranean landscape comprising a variety of habitats regenerating after fire. The findings clearly demonstrate that a variety of nesting substrates and nest building materials have key roles in organising the composition of bee communities. 3. The availability of bare ground and potential nesting cavities were the two primary factors influencing the structure of the entire bee community, the composition of guilds, and also the relative abundance of the dominant species. Other nesting resources shown to be important include availability of steep and sloping ground, abundance of plant species providing pithy stems, and the occurrence of pre-existing burrows. 4. Nesting resource availability and guild structure varied markedly across habitats in different stages of post-fire regeneration; however, in all cases, nest sites and nesting resources were important determinants of bee community structure.

/pdf/role-of-nesting-resources-in-organising-diverse-bee-4xao78trxo.pdf

Amots Dafni

Papers

Pollination ecology: a practical approach.

Linking bees and flowers: how do floral communities structure pollinator communities?

Practical Pollination Biology

Mimicry and Deception in Pollination

Role of nesting resources in organising diverse bee communities in a Mediterranean landscape