Wild bees are important pollinators that have declined in diversity and abundance during the last decades. Habitat destruction and fragmentation associated with urbanization are reported as part of ...the main causes of this decline. Urbanization involves dramatic changes of the landscape, increasing the proportion of impervious surface while decreasing that of green areas. Few studies have investigated the effects of urbanization on bee communities. We assessed changes in the abundance, species richness, and composition of wild bee community along an urbanization gradient.
Over two years and on a monthly basis, bees were sampled with colored pan traps and insect nets at 24 sites located along an urbanization gradient. Landscape structure within three different radii was measured at each study site. We captured 291 wild bee species. The abundance of wild bees was negatively correlated with the proportion of impervious surface, while species richness reached a maximum at an intermediate (50%) proportion of impervious surface. The structure of the community changed along the urbanization gradient with more parasitic species in sites with an intermediate proportion of impervious surface. There were also greater numbers of cavity-nesting species and long-tongued species in sites with intermediate or higher proportion of impervious surface. However, urbanization had no effect on the occurrence of species depending on their social behavior or body size.
We found nearly a third of the wild bee fauna known from France in our study sites. Indeed, urban areas supported a diverse bee community, but sites with an intermediate level of urbanization were the most speciose ones, including greater proportion of parasitic species. The presence of a diverse array of bee species even in the most urbanized area makes these pollinators worthy of being a flagship group to raise the awareness of urban citizens about biodiversity.
Intensive agricultural systems often expose honey bees (Apis mellifera L.) to large temporal variations in the availability (quantity, quality and diversity) of nutritional resources. Such ...nutritional irregularity is expected to affect honey bee health. We therefore tested under laboratory conditions the effect of such variation in pollen availability on honey bee health (survival and nursing physiology-hypopharyngeal gland development and vitellogenin expression). We fed honey bees with different diets composed of pollen pellets collected by honey bees in an agricultural landscape of western France. Slight drops (5-10%) in the availability of oilseed rape (Brassica napus L.) pollen resulted in significant reductions of all tested variables. Despite some variations in taxonomic diversity and nutritional quality, the pollen mixes harvested over the season had a similar positive influence on honey bee health, except for the one collected in late July that induced poor survival and nursing physiology. This period coincided with the mass-flowering of maize (Zea mays L.), an anemophilous crop which produces poor-quality pollen. Therefore, changes in bee health were not connected to variations in pollen diversity but rather to variations in pollen depletion and quality, such as can be encountered in an intensive agricultural system of western France. Finally, even though pollen can be available ad libitum during the mass-flowering of some crops (e.g. maize), it can fail to provide bees with diet adequate for their development.
The relationships between landscape intensification, the abundance and diversity of pollinating insects, and their contributions to crop yield, quality, and market value are poorly studies, despite ...observed declines in wild and domesticated pollinators. Abundance and species richness of pollinating insects were estimated in ten fields of spring oilseed rape, Brassica napus var. SW Stratos™, located along a gradient of landscape compositions ranging from simple landscapes dominated by arable land to heterogeneous landscapes with extensive cover of semi-natural habitats. In each field, we assessed the contribution of wind and insect pollination to seed yield, seed quality (individual seed weight and oil and chlorophyll contents), and market value in a block experiment with four replicates and two treatments: (1) all flowers were accessible to insects, self and wind pollination, and (2) flowers enclosed in tulle net bags (mesh: 1 × 1 mm) were accessible only to wind and self pollination. Complex landscapes enhanced the overall abundance of wild insects as well as the abundance and species richness of hoverflies. This did not translate to a higher yield, probably due to consistent pollination by honey bees across all fields. However, the pollination experiment showed that insects increased seed weight per plant by 18% and market value by 20%. Seed quality was enhanced by insect pollination, rendering heavier seeds as well as higher oil and lower chlorophyll contents, clearly showing that insect pollination is required to reach high seed yield and quality in oilseed rape. Our study demonstrates considerable and previously underestimated contributions from pollinating insects to both the yield and the market value of oilseed rape.
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.
This meta-analysis summarizes the results of research on the relationships of majority group members’ endorsement of assimilation, colorblindness, multiculturalism, and the relative relationships of ...colorblindness and multiculturalism to ethnic prejudice. Random effects analyses found that assimilation was positively related to explicit prejudice (g. = 0.80), multiculturalism was negatively related to both explicit (g. = −0.26) and implicit prejudice (g. = −0.19), and colorblindness was negatively related to explicit prejudice (g. = −0.07). Multiculturalism was more closely associated with low prejudice than colorblindness (g. = 0.15). Effect sizes varied as a function of methodology (experimental vs. correlational), country in which research was conducted (United States vs. other countries), and, in experimental studies of multiculturalism, type of prime used (abstract vs. concrete). Discussion points include methodological issues, groups used as targets of prejudice, national diversity norms, additional issues raised in the studies reviewed, and directions for future research.
There is mounting evidence of pollinator decline all over the world and consequences in many agricultural areas could be significant. We assessed these consequences by measuring 1) the contribution ...of insect pollination to the world agricultural output economic value, and 2) the vulnerability of world agriculture in the face of pollinator decline. We used a bioeconomic approach, which integrated the production dependence ratio on pollinators, for the 100 crops used directly for human food worldwide as listed by FAO. The total economic value of pollination worldwide amounted to €153 billion, which represented 9.5% of the value of the world agricultural production used for human food in 2005. In terms of welfare, the consumer surplus loss was estimated between €190 and €310 billion based upon average price elasticities of − 1.5 to − 0.8, respectively. Vegetables and fruits were the leading crop categories in value of insect pollination with about €50 billion each, followed by edible oil crops, stimulants, nuts and spices. The production value of a ton of the crop categories that do not depend on insect pollination averaged €151 while that of those that are pollinator-dependent averaged €761. The vulnerability ratio was calculated for each crop category at the regional and world scales as the ratio between the economic value of pollination and the current total crop value. This ratio varied considerably among crop categories and there was a positive correlation between the rate of vulnerability to pollinators decline of a crop category and its value per production unit. Looking at the capacity to nourish the world population after pollinator loss, the production of 3 crop categories – namely fruits, vegetables, and stimulants - will clearly be below the current consumption level at the world scale and even more so for certain regions like Europe. Yet, although our valuation clearly demonstrates the economic importance of insect pollinators, it cannot be considered as a scenario since it does not take into account the strategic responses of the markets.
We study, on certain Banach spaces
X
, families of weighted composition operators. Notably, we show that if this family forms a strongly continuous semigroup, then its infinitesimal generator (
Γ
,
D
...(
Γ
)
) is given by
Γ
f
=
g
f
+
G
f
′
with
D
(
Γ
)
=
{
f
∈
X
|
g
f
+
G
f
′
∈
X
}
where
g
,
G
are holomorphic functions. Moreover, our second main result is to study the reciprocal implication. That is, if
(
Γ
,
D
(
Γ
)
)
, defined as above, generates a strongly continuous semigroup, then this one is a family of weighted composition operators.
The Hidden Cost Trappey, Bernard E.
The American journal of medicine,
April 2023, 2023-Apr, 2023-04-00, 20230401, Letnik:
136, Številka:
4
Journal Article
PDF
