Abstract
Almost 50 years ago, Michael Rosenzweig pointed out that nutrient
addition can destabilize food webs, leading to loss of species and
reduced ecosystem function through the paradox of enrichment. Around the
same time, David Tilman demonstrated that increased nutrient loading
would also be expected to cause competitive exclusion leading to
deleterious changes in food web diversity. While both concepts have
greatly illuminated general diversity-stability theory, we currently
lack a coherent framework to predict how nutrients influence food web
stability across a landscape. This is a vitally important gap in our
understanding, given mounting evidence of serious ecological disruption
arising from anthropogenic displacement of resources and organisms.
Here, we combine contemporary theory on food webs and meta-ecosystems to
show that nutrient additions are indeed expected to drive loss in
stability and function in human-impacted regions. However, this loss in
stability occurs not just from wild oscillations in population
abundance, but more frequently from the complete loss of an equilibrium
due to edible plant species being competitively excluded. In highly
modified landscapes, spatial nutrient transport theory suggests that
such instabilities can be amplified over vast distances from the sites
of nutrient addition. Consistent with this theoretical synthesis, the
empirical frequency of these distant propagating ecosystem imbalances
appears to be growing. This synthesis of theory and empirical data
suggests that human modification of the Earth’s ecological connectivity
is “entangling” once distantly separated ecosystems, causing rapid,
expansive, and costly nutrient-driven instabilities over vast areas of
the planet. The corollary to this spatial nutrient theory, though –
akin to weak interaction theory from food web networks – is that slow
spatial nutrient pathways can be potent stabilizers by moderating flows
across a landscape