As well as direct interaction and disturbance, avoidance of interspecific chemical cues and resource competition have the potential to alter pollinator foraging movements. Global human population growth is putting greater pressure on agricultural production. There is concern over how to meet the increasing demand for food, while at the same time safeguarding ecosystems and biodiversity. In the future, land currently under agricultural production will have to be more intensively managed to increase yields and/or more land will have to be converted to agriculture. Given the negative impact agriculture has already had on biodiversity, it is important that future steps to increase production be made environmentally sustainable. In the last 50 years, the fraction of agricultural production requiring biotic pollination has more than tripled. When compared with crops that are not pollinator-dependent, those that are moderately pollinator-dependent have shown slower growth in yield and faster expansion in area from 1961 to 2006. Almond is a mass-flowering, varietally self-incompatible crop species, hydroponic nft gully highly dependent on biotic pollination. Almond orchards are generally planted with alternating rows of two or more varieties.
Planting a single variety per row facilitates harvest, but complicates pollination because pollen must be transferred between rows to achieve fruit set. To allow for management activities, trees between rows are further apart than those within the same row . Apis mellifera tend to forage within a tree and then move down the same row, probably because less effort is required to move to the next tree in the same row or because the rows act as visual markers that influence movement. This foraging pattern means A. mellifera tend to move more incompatible pollen, limiting their pollination effectiveness. In almond, we investigated whether the presence of nonApis bees affected the behaviour and pollination service of the dominant pollinator species, A. mellifera. Often almond orchards are isolated from natural habitat and non-Apis bees can be completely absent. Therefore, we were able to compare A. mellifera behaviour and pollination effectiveness in diverse bee communities with orchards lacking non-Apis bees. Here, we refer to pollinator effectiveness as the probability an ovule is fertilized following a single visit. We complemented our intensive field sampling with observations in a controlled cage environment, where A. mellifera were introduced along with the blue orchard bee Osmia lignaria Say. We hypothesized that where non-Apis bees were present, such as in sunflower, interspecific interactions would cause A. mellifera to more frequently move between rows. We further hypothesized that an increase in between-row movements by A. mellifera would increase their pollination effectiveness and increase fruit set .
Our findings show that increased pollinator diversity can synergistically increase pollination service through species interactions that alter the behaviour and resulting functional quality of a dominant pollinator species. This highlights a largely unexplored facilitative component of the benefit of biodiversity to ecosystem services. Total bee visitation rates were similar between orchard types, and the visitation rate of A. mellifera was lower in orchards with non-Apis bees. However, A. mellifera pollination effectiveness was greater and fruit set was higher when non-Apis bees were present. Apis mellifera increased their proportion of movement between tree rows when non-Apis bees were present, thereby improving pollination effectiveness. More successful pollen tube growth translated into significantly higher fruit set in the orchards where non-Apis bees were present. The greater proportion of between row movements by A. mellifera individuals most probably resulted in the deposition of more compatible pollen, since pollen from the same variety generally does not set fruit . This synergistic effect of the presence of non-Apis bees suggests that maintaining biodiversity in agricultural ecosystems could provide unrecognized benefits, and it offers exciting opportunities for the integration of more diverse pollination systems to improve the longer-term sustainability of crop production for almond and similar crops. Unlike in sunflower, very few direct interactions were observed between A. mellifera and non-Apis bees. One potential mechanism for the increased proportion of inter-row movement of A. mellifera in the presence of other non-Apis bees is linked to resource depletion. Because some non-Apis bees can fly at lower temperatures than A. mellifera, and therefore earlier in the day, it may be that if A. mellifera begin foraging and find flowers have already been depleted then they increase the distance of their foraging flights. Alternatively, it may be related to the scent marks left by non-Apis bees on the flowers.
Apis mellifera have been shown to avoid visiting flowers that have been marked by bumble bees, and it may be that as well as avoiding the flowers they also shift their foraging location. Given that A. mellifera tend to move down the same row, if a response to perceived resource competition is to shift foraging locations, this could be expected to involve movement across rows. However, at present the mechanism for the increased between-row movements when non-Apis bees are present is unknown. In the controlled cage environment, the steeper increase in the number of pollen tubes initiated with increasing pollen deposition in the mixed cage and the higher fruit set supports the findings from the open orchards that more compatible pollen is being moved when pollinator communities are diverse. Because there was only one cage per treatment, the data from the cages are only descriptive, but they do support the findings from the open orchards. Future work should attempt to replicate similar treatments. The greater fruit set in the mixed cage when the visitation rate was lower than in the A. mellifera cage may be due to the slightly higher proportion of between-row movements in the mixed cage. Although the differences in movement were not great, the pollen tube data suggest that more pollen was moving between varieties in the mixed cage. The size of the cages limited the opportunity for between-tree flights. This and the relatively low visitation rate of O. lignaria in the cages compared with the open orchards may explain why the difference in pollen tubeformation and fruit set between the cages was less than in the open orchards. The price of California almond in 2011 was approximately $1.79 per pound and production was estimated at 2670 lbs per acre . If a 5 per cent increase in fruit set as calculated from the controlled cage environment translated into an equivalent increase in production, farmers would make $239 more per acre . This estimate from cages may be a lower bound compared with open orchards. Sampling effects and complementarity have been the primary explanations for a positive relationship between biodiversity and ecosystem function. Here, we show a different mechanism, possibly due to interspecific competition, where community composition alters the behaviour of a service-providing organism with a positive knock-on effect for the ecosystem service. Our results show alterations in A. mellifera foraging behaviour when a diverse community of other bees are present, and suggest almond yield can be increased by encouraging wild bees in the orchards. As such, dutch buckets for sale natural habitat near almond orchards should be conserved to protect wild bee communities. The availability of A. mellifera is not predicted to increase at the same rate as demand for their services in agriculture. Thus, increasing the pollination effectiveness of A. mellifera and conserving wild pollinator communities could help increase crop yields. The synergistic combination of A. mellifera and non-Apis bees represents a sustainable way to improve crop pollination services, but the generality of such effects still need to be tested across multiple crop systems.The two coffee species of commercial value, Coffea arabica and Coffea canephora , both originate from Africa; the former has generally preferred taste qualities, and the latter exhibits higher yield and pest resistance . Coffea arabica dominates global coffee landscapes, accounting for 60% of the total coffee volume produced . Although coffee’s center of origin lies in Ethiopia, major global dispersal of the bean occurred when Arab and European traders introduced the beverage to Western Europe in the early 1500s . By the latter half of the 1800s, coffee plantations of both C. arabica and C. canephora flourished throughout the American tropics; by the 1970s, coffee’s cultivation dominated more than 8.8 million hectares of tropical landscapes. Between 1970 and 1990, the global coffee area and average yields increased by 25% , and global production increased by 58% .
Interestingly, although the global area decreased to 10.2 million ha between 1990 and 2010 , production still climbed 36%, which is evidence of an overall intensification in several key countries , coffee abandonment in others , and the rapid expansion of high-yield coffee in new countries . Brazil, for instance, saw a 112% jump in production with only a 12% increase in coffee area between 1996 and 2010, growth spurred by intensification that resulted in an 89% yield increase over that period , and recognition from coffee experts that production there has been highly industrialized . Since the mid-1980s, exports of robusta coffee have increased by 92%, led by a number of Asian countries, with Vietnam being the prime example, exhibiting hand-in-hand increases in both area and intensification . Robusta yields there soared from a historical average of 450 kg per ha prior to the 1950s to 1558 kg per ha by 2004 , more than double the global yield average at the time, which reveals that a species shift alone does not explain yield increases. Given that coffee area decreased globally by 9% between 1990 and 2010, whereas world production increased by 36%, we posit that intensification is one of the major drivers of shifting coffee cultivation practices. A closer look reveals that the shift in production between 1990 and 2010 was regional: 45% of the nations exhibiting decreases were in Africa, whereas Asian countries accounted for 35% of those with increased production . When the first comprehensive studies of coffee and biodiversity emerged in 1996, the top three producing countries were Brazil, Colombia, and Indonesia. Currently, Brazil, Vietnam, and Indonesia top the list, accounting for 57% of the 8.2 million metric tons produced in 2010. In Vietnam alone, the cultivated area increased by 731%, yields by 45%, and the total production by 1102% between 1990 and 2010 . In contrast, the past 20 years reveal coffee area declines exceeding 20% in Ecuador, Colombia, Côte d’Ivoire, Mozambique, Madagascar, Tanzania, and Rwanda . The contrasting and heterogeneous changes in global coffee cultivation result from multiple factors, including region-specific economic development patterns, political conflict, cultural practices, land values, wages, and labor. For example, deforestation accompanied increases in coffee area in Vietnam, Indonesia, Nepal, and Panama . In contrast, in places where the coffee area has declined, such as Costa Rica and Ecuador, the expansion of high-yield agriculture has caused a decrease in coffee prices, which has, in turn, resulted in the abandonment of marginal agricultural lands in combination with increased land prices due to urbanization. Higher land values due to exurbanization often displace coffee cultivation in places like Panama’s Boquete and Chiriquí regions, Costa Rica, and Guatemala— areas now popular as retirement destinations . In a number of countries, waves of political and social instability have reduced investment in coffee cultivation , but sustained global prices after 2005 have spurred expansion in other countries . In other regions, the draw of better urban wages or displacement by other cash crops, such as cacao , has reduced the area of coffee production. Despite variation in global coffee production, the majority of coffee is still produced by smallholders managing less than 10 ha of coffee , as has been documented in Asia and in Africa . Likewise, in Central America, smallholders represent 85% of coffee producers but control only 18% of coffee production lands . In some coffee-producing countries, such as Rwanda, coffee farm sizes are so small that the majority of farms are measured by the number of coffee bushes instead of in ha , whereas in many Mesoamerican smallholder farms, stand densities are as high as 6700 coffee bushes per ha . These patterns in farm size tend to shift, depending on coffee prices and government incentives, as is evidenced in Latin America, where a decrease in the number of large estates and an increase in the number of smallholders and microproducers occurred directly after the 1999 coffee crisis, when coffee prices dropped to century lows . In the Costa Rican coffee district of Agua Buena, the proportion of farmland dedicated to coffee production diminished from 52% to 24% between the years 2000 and 2009, whereas the proportion of pasture land increased from 31% to 50%, largely because of basement level international coffee prices .