Amphibian and reptilian diversity as a tool for assessing the ecological values of agricultural land uses
Yahel Porat, Tamar dayan and Yohay Carmel
The main cause for the contemporary biodiversity crisis, is the enormous human
population growth, which exploit natural systems, and alter it into different land uses,
in order to maintain human wellbeing. Agriculture, together with pasture, is covering
approximately 40% of the earth continental surface. During the last 50 years, a
process of agricultural intensification have been occur, including the utilization of
pesticides, fertilizers, irrigation and drainage modern systems, reduction of crops
types and cycles at the farm level , transformation of cultivating systems, the loss of
lands natural vegetation cover in the margins of agricultural lands and so on. This
process leads to a drastic reduction in the structural complexity of agricultural areas,
expressed in the spatial scale (at the plot level, and the entire agricultural landscape as
well), and in the uniformity of habitat conditions during the year. It is well accepted
now days, that general reduction in the structural complexity of agricultural areas is
the main cause to the biodiversity reduction which characterize them, and that
agriculture is the single land use most affecting species extinction in the world.
Considering this, the concept of “Wildlife Friendly Agriculture”, had been developed
in the last decades in Europe, perceiving the agricultural landscape as an “Agro-eco
systems”: a mosaic of natural vegetation patches, combined with different agricultural
land uses. Biodiversity, which is crucial to the function of the whole system, is found
in all the mosaic parts. According to that concept, the key to a long term sustainability
of the agro-eco system is the reduction of the gaps between the different patches, and
preserving maximum variance in time and space. Further more, according to this
concept, policy of nature conservation inside those systems, should focus on
ecological research, dealing with the relationship between the different patches. In
this research we choose to explore this relationship, as well as species diversity and
composition index, and the conservation value for reptiles and amphibians species
diversity, to be found in a series of agricultural land uses, characterizing the agroecosystems
in the mediterranean region of Israel .In addition, we asked what are the
causes effecting species richness of different land uses, and what is the importance of
structural complexity, concerning this. Those Taxonomic groups have been chosen
because recently it had been discovered that they are the most threaten among
vertebrate groups, due to global change in the distribution of land uses, as well as
having good ability to function as systems ecological health indicator. In addition, their sampling and identifying in the field is straight-forward, causing minimal
disturbance to the farmer. The study had been carried out in Ramot-Yisachar at the
eastern lower Galilee, which is a semi arid region, characterized by grass scrubland
with few Ziziphus sp. shrubs and trees. The chosen land uses where : cattle graze
lands located in grass scrubland, Wadies preserving narrow strips of native vegetation
and rocks between the cultivated plots, almond groves preserving grass strips between
trees strips, preventing soil erosion and wheat fields being cultivated without tillage.
Eight sampling plots had been placed in each one of two sub regions (16 plots total)
presenting different landscape patterns: the first one, in the northern region, preserve
many large graze lands, surrounding cultivated plots being penetrating by many non
cultivated wadies. The second one, in the southern region, preserving few small
graze lands, surrounding by large cultivated area contains few non cultivated wadies.
Species diversity was sampled out at seven different periods of time, during October
2009 –April 2010, using distance and number of covers constrained search, and also
pitfall trapping. The study results show that the structural complexity of the
agricultural land use have a decisive effect upon the reptiles and amphibians species
diversity to be found inside of it, and that land uses, which preserve the culture of the
native vegetation and rock, have high value of conservation for reptiles and
amphibians species. All the species that had been found inside the intensive
agricultural land uses, are a subset group of the species that had been found in the
graze lands and wadies plots, characterized by the most widespread, and durable
species. Graze lands, as a land use preserving large area of high structural complexity,
have a high value for reptiles and amphibians species diversity. Non cultivated wadies
between the agricultural plots, as a land use with linear shape and high structural
complexity, have a medium value for conservation of reptiles and amphibians species
diversity.Even though few vulnerable speacies which exist in wide scale graze lands,
are excluded from those wadies are, yet, they are the most valuable land use within
the intensive agricultural area itself, therefore might function as “keystone structure”
for the entire biodiversity inside agro-eco systems of that region, as long as they’ll be
properly managed. On the opposite, intensive agricultural land uses, which the culture
of native vegetation and rock had been cleared inside of them, have a low value for
reptiles and amphibians species diversity, but there is an internal hierarchy in their
values. Almond groves managed with soil preserving management, as a medium
structural complexity land use, have some value for conservation of reptiles and amphibians species diversity, as opposed to wheat fields which have no value at all. It
had been found that addition of structural components, such as trees and native
vegetation strips, characterizing almond groves for example, contributes to the ability
of intensive agriculture land uses to maintain reptiles and amphibians society inside of
them. This society is mostly composed of low number of widespread generalist
species, which the conditions of the intensive agricultural habitat, so as the minority
of competitors and predators, make them able to thrive. The existence of those species
in intensive agricultural land uses, might assist to the conservation of their metapopulation
in the entire agro-eco system, incase of specific extinction in graze lands
and wadies (as a result of wild fire for example). It also might assist in terms of pest
control inside the agricultural plot. Those almond groves, might function also as a
distribution corridors for individuals from more vulnerable species, through the
intensive agricultural matrix. It had been found out, that wheat field are acting as
hostile territory for most reptiles and amphibians species. The study results, are
strengthening the concept of “Wildlife Friendly Agriculture”, emphasize the necessity
in abandoning the concept which perceive agricultural regions as a uniform hostile
matrix for biodiversity, while also emphasize the urgent need in the ecological
management of agro-eco systems in Israel. In the mediteranean region of Israel, which
agriculture is an inseparable part of the open spaces inside of it (and also assist to
protect them), we should adopt those concept urgently, in order to preserve the last
significant biodiversity values which survive in many large scale agro-eco systems.
That should be done, by developing multi disciplinary conservation tools.
Recommendations for planning and management agro-eco systems are being
discussed elaborately.
View full thesis here (Hebrew)