Introduction: Biodiversity in human-transformed landscapes
For centuries, global human-driven Land Use and Cover Change (LUCC) has
spread the so-called ‘anthropogenic habitats’ in many regions, like the
Mediterranean, thus determining biodiversity and ecosystem functioning
in human-transformed landscapes (1 ).
The impacts have been manifold,
strongly differing from the mosaic landscapes of past and present
organic mixed farming adapted to site-specific natural endowments, up to
the land cover homogenization driven by industrial farming and animal
feeding reliant on fossil fuels
combined with spontaneous reforestation ensuing rural abandonment
(2 ,3 ,4 ). Effects of LUCC on biodiversity are
largely known (5 ,6 ), and they include a general
decrease in species richness but also changes in species composition due
to rarefaction of habitats specialists and expansion of generalists and
cosmopolitan species, as well as invasions by alien species
(7 ,8 ) through increasing propagule pressure and
disturbance levels (9 ,10 ). All these impacts lead to
biotic homogenization in most-human transformed regions (11 ).
Biodiversity components associated to human-transformed landscapes are
clear examples of these changes. For example, population decline of most
bird and butterfly species is believed to be linked to the loss and
fragmentation of natural habitats, but also to the abandonment of
traditional land-use management in rural areas that led to both
agricultural intensification and forest encroachment
(12 ,13 ). These LUCC effects added to other global
change components, like climate change (14 ,15 )
combined with homogenization of cultural landscapes (16 ).
Habitat specialists often are the most negatively affected, while
generalists can even take profit of them (17 ).
As a result, human-transformed landscapes are the outcome of a shifting
interplay between the spatial patterns of land-use types driven by the
energy flows of human activity, and their associated ecological
processes (18 ,19 ). A widely acknowledged consensus in
conservation biology, framed in the intermediate disturbance hypothesis
(20 ), points out that landscape heterogeneity is key to
maintaining biodiversity peaks at intermediate disturbance levels
through the interaction between the ecosystem patch diversity and the
ecological requirements to activate the dispersal abilities of species
that come from less disturbed patches or colonize the most disturbed
ones (21 ,22 ).
However, the outcome also depends
on the intensity and spatial distribution of the anthropogenic
socio-metabolic flows at play (23 ,24 ).
This recurrent interaction between
landscape patterns and socioecological pressures opens a research field
on how the complexity of the energy flows driven by farming, livestock
rearing, and forestry ‘imprint’ diverse spatial patterns of human
land-uses that give rise to heterogeneous or homogeneous landscapes
capable to house different biodiversity levels
(25 ,26 ).
The fundamentals of this research
agenda can be found in Morowitz’s theorem that says that a flow of
energy through a system is a necessary and sufficient condition for
generating an organized structure, although ephemeral in time
(27 ). The structures of living systems that emerge and evolve
towards a self-reproducing complexity allow to keep information
organized and to transfer energy with higher efficiency away from
thermodynamic equilibrium (28 ). Without doubt, this increase in
internal complexity is achieved by exporting entropy to the environment,
as any living organism is an energy dissipative structure with multiple
metabolic cycles interrelated through a space-time heterogeneous base
(29 ). This thermodynamic concept of organisms has close
similarities to ecosystems’ sustainability, which is directly related to
information-complexity and inversely to entropy.
When a living system becomes more
complex it is also metabolically more efficient because it increases the
internal information instead of its energy intake, thereby also reducing
external entropy (30 ).
Margalef principle indicates that ecosystems succession tends to a
decrease in the photosynthetic Net Primary Production (NPP) growth rate.
In other words, entropy combined with information increases diversity,
not the production of uniformity (31 ). In the same vein,
complex agroecosystems can store more energy and information at some
points that reduce internal entropy, thanks to the exploitation of other
spaces of lower complexity but larger NPP production rate within a joint
encompassing landscape functional structure. Many traditional
Mediterranean agroecosystems were the result of this type of balance
between exploitation and conservation through the spatial localization
of different gradients of human intervention, a wise intermediate
disturbance pattern resulting in heterogeneous landscape mosaics
(32 ).
The combination of an energy-flow
pattern driven by complex information on how energy is redistributed
across space is a good starting point for modelling the human-landscape
relationships. According to
Margalef (31 ), ‘the relationship between the external
energy inputs and the dimensions that characterize the spatial patterns
of its distribution ’ gives rise to the functional structure of
landscape mosaics capable to host higher biodiversity than other
homogeneous land covers. In order to test this hypothesis, Marull et al.
(33 ,54 ) developed an Energy–Landscape Integrated
analysis (ELIA ) of agroecosystems which accounts both the
investment of energy stored within (E ) and the information held
in the whole network of socio-metabolic energy flows (I ), to
correlate their interplay (E·I ) with the functional structure of
the resulting cultural landscape (L ). Then, we use here this
energy-information-structure model (Fig. 1 ) to predict the
locations of two important biodiversity components, butterflies and
birds, in the human-transformed landscapes here accounted as an
empirical example (31 ). The aim is to test Margalef’s
hypothesis that the complex landscape mosaics of traditional organic
agriculture were, and continue to be, good for biodiversity
conservation. This means discussing if the energy reinvested and
redistributed by farming-driven metabolic flows can lay the foundations
to study the linkages that exist between social metabolism, landscape
ecology and biodiversity, to better inform sustainable-oriented land use
policies.
[Insert Figure 1 here]
Testing Margalef’f hypothesis
requires specifying and accounting the ecological disturbance exerted by
the information-driven external energy that farmers incorporate to the
landscape. The Human Appropriation of Net Primary Production (HANPP) is
a quantitative estimate of the potential annual biological productivity
reduced by human activities (34 ,35 ).
It provides a first approach to
the interplay between the anthropogenic disturbances and the wildlife
ability to withstand them.
Intermediate HANPP values
can maintain greater biodiversity
in human-modified landscapes than higher ones that would largely
decrease habitat differentiation and the provision of enough food chains
free from human colonization (36 ). On this light, Marull et al.
(33 ) developed an Intermediate Disturbance Complexity
(IDC ) model to assess how different levels of anthropogenic
disturbance at regional scale affect landscape functional structure.
Results show a hump-shaped relationship between landscape complexity,
free NPP available for non-domesticated species, and biodiversity levels
(33 ,37 ). However, this strongly depends not only on
the overall flux balance of photosynthetic biomass but on the intensity
and distribution of socio-metabolic flows associated to either land-use
mosaics or homogeneous land covers of agroecosystems (23 ,24 ,38 ).
The ELIA modelling goes a step forward from the previousIDC explorations of the links between intermediate levels of
socio-metabolic human disturbance and the ecological functioning of
cultural landscapes carried out at regional scale (37 ). It
measures E as the quantity of energy remaining in the
agroecosystem, and I as the complexity of the network of flows
which allows farmers to reproduce the landscape fund components thanks
to the information embedded in the system. Both indicators, E andI , bring to light how the energy-information interplay gives rise
to human-transformed landscapes. They do so by relating them toL , the landscape ecology metrics that assess the ‘imprint’ of the
energy flows driven by farmers. We surmise that the interplay betweenE and I jointly leads to complexity, understood as a
balanced level of intermediate self-organisation (39 ). We also
assume that the complexity of energy flows (E ·I ) is
related to the landscape functional structure (L ). The cyclical
nature of these matter-energy flows is relevant in order to grasp the
emergent complexity and the greater information held within
agroecosystems, since they imply an internal maximisation of some
less-dissipative fractions of societal metabolism. The complexity and
information carried out by these energy loops lay the foundations to
better understand and develop more sustainable human-managed landscapes.