The Ecological Importance of Bees
How the world's most important pollinators sustain both natural ecosystems and human food supplies
A The relationship between bees and flowering plants is one of the most consequential partnerships in the history of life on Earth. It began in the early Cretaceous period, when a group of ancestral wasps gradually shifted from a predatory diet of other insects to one based on the pollen and nectar of flowering plants. In collecting these plant-based foods for themselves and their larvae, these proto-bees inadvertently carried pollen grains on their bodies from flower to flower, enabling cross-pollination. Over millions of years, flowers evolved structures and chemistry that increasingly rewarded bee visits -- richer nectar, more accessible pollen, colours and scents precisely calibrated to bee sensory systems -- while bees developed bodies and behaviours ever better suited to exploiting what flowers offered. The result is an intricate mutual dependence that today sustains much of the world's plant diversity.
B The agricultural and economic significance of this relationship is difficult to overstate. It is estimated that bees are responsible for pollinating approximately one third of the food that humans consume, either directly -- through pollination of fruit, vegetable, and nut crops -- or indirectly, through the pollination of the forage plants on which livestock depend. The annual value of crops whose yields depend on bee pollination has been estimated at over one trillion US dollars globally. Within this total, the contribution of managed honey bee colonies far exceeds the monetary value of the honey they produce: crop pollination services are thought to be worth approximately fifty times as much as the honey crop itself.
C Despite the apparent harmony of this relationship, bees and flowers are not partners in any straightforward sense -- they are economic competitors whose interests only partially align. A flower must attract enough bee visits to ensure pollination but cannot afford to provide so much nectar that a single bee becomes fully satisfied and returns to its nest without visiting further flowers. A bee, meanwhile, seeks to gather the maximum possible quantity of food while expending the minimum energy. It must constantly evaluate the reward on offer against the cost of travel and extraction, making decisions that closely resemble those of a rational consumer in a competitive marketplace. The ecologist's description of this relationship as a form of mutual exploitation -- in which each party extracts what it can while conceding as little as possible -- comes closer to the truth than the popular image of bees and flowers working in harmonious cooperation.
D The importance of bees extends well beyond their role in agriculture. In natural ecosystems, bees are the primary pollinators of the majority of wild flowering plant species. The fruits, seeds, and berries that result from this pollination sustain a wide range of birds and mammals. Ecosystems from which bees were removed would rapidly become impoverished as the plant species dependent on their services declined, triggering cascading effects through the food chains they support. In tropical rainforests, where some bee species forage over distances of more than twenty kilometres, bees function as what ecologists call keystone species -- organisms whose removal would cause disproportionately large disruptions to the wider ecological community.
E Understanding how bees navigate and forage has become increasingly important to conservation planning. Research has shown that certain bee species learn and memorise the locations of food sources, returning to them along consistent routes in a behaviour that ecologists call trap-lining. This is particularly significant in tropical forests, where individual trees of any given species may be sparsely distributed across a large area. A single large bee may be the sole pollinator capable of reliably connecting widely separated individuals of the same tree species, making it essential not only to the reproduction of that tree but to the genetic diversity of the entire population.
F This knowledge has direct implications for how conservationists calculate the minimum viable size of protected forest areas. If the bee species that pollinate a given set of tree species have foraging ranges of twenty kilometres or more, then forest reserves that appear adequate on the basis of their area alone may in reality be too small or too isolated to sustain long-term pollination. Conservation biologists now argue that decisions about the boundaries of protected areas must incorporate detailed knowledge of the foraging behaviour and flight range of the key pollinator species present -- a requirement that demands far more research than has so far been completed.
G Bee populations worldwide are under threat from a combination of pressures: habitat loss, the widespread application of pesticides, the spread of parasitic mites and viral diseases, and climate change, which is altering the seasonal timing of both bee activity and flower production in ways that can disrupt their synchrony. These pressures have been particularly severe for managed honey bee colonies in Europe and North America, where colony losses in some years have exceeded thirty percent. Wild bee species, which are harder to monitor and receive far less attention than honey bees, may be suffering even greater declines. Given the central role that bees play in sustaining both agricultural productivity and natural ecosystem function, understanding and reversing these declines must be counted among the most urgent priorities in environmental science.