**1. Introduction**

Soil is a dynamic and complex system: its physical and chemical nature, with a porous structure, immense surface area, and extremely variable supply of organic materials, food, water, and chemicals, provides habitats for many living beings among which arthropods that make up an essential component. Five groups are chiefly represented: Isopoda, Myriapoda, Insecta,

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Acari, and Collembola [1]. The oniscoids (Oniscidea) with more than 3600 species belonging to 5 major taxonomic groups—Diplocheta, Tylida, Microcheta, Synocheta, and Crinocheta [2]—are an important component. Isopod species composition and diversity were studied in several habitats within the Mediterranean region. Terrestrial isopod community structure differs across habitat types (natural area, seminatural area, agroecosystems, and protected area), vegetation structure, and altitude [3–12].

a seasonal breeding followed by a period of sexual rest. The information available on terrestrial isopod reproduction patterns in temperate regions is largely for species occupying mesic habitats [31–42]. The reproductive phenology of xeric species in temperate regions has been studied extensively only for populations in the Middle East desert [32, 43–45]. These desert species that are well adapted to an arid environment differ considerably in their breeding seasons and strategies [46]. The burrowing species *Hemilepistus reaumurii* and *Hemilepistus klugii* are semelparous and reproduce during a very short time of the year: April and May for *H. reaumurii* and April for *H. klugii*. The other xeric species, which do not live in the burrows, are iteroparous. These are *Porcellio ficulneus* and *Porcellio barroisi*, which breed in spring, and *Armadillo albomarginatus*, which breeds in autumn. Both *Porcellio olivieri* and *Agabiformius obtusus* show continuous reproduction under laboratory conditions. Reproductive success in these terrestrial isopods depends on the largest size and number of offspring a female may have. The females of terrestrial isopods produce eggs and develop, following a parturial molt, a marsupium, which is not only a pouch for carrying eggs but plays the same role as a uterus that provides a transfer of substances between the female and its brood [47]. These activities require high energy costs for its offspring [48] that limit the future reproductive potential of the female. Given these constraints, better reproductive success can be achieved by extending care to offspring. Investing in already expensive offspring may be a better choice [44]. This hypothesis seems to explain the high parental investment of some terrestrial isopods in arid regions. The semelparous and burrowing species *H. reaumurii* shows two-parental care with sustainable family cohesion [2]. Indeed, the parental energy investment continues for several months after mancae release, until the young isopods disperse.

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Oniscoids have succeeded, thanks to a number of adaptations noted above, to become the only large group of crustaceans to be completely terrestrial. Among them, Species that do not have effective protection against desiccation have been restricted to mesic habitats [49]. However, other species have managed to colonize semiarid and arid habitats, and some have even managed to thrive in the desert. These adaptations have made the nine species of *Hemilepistus* the most abundant detritivores of the macrofauna of many arid areas of Asia Minor [26, 45, 50]. All of them are burrowing species. The model species *H. reaumurii*, widely distributed in North Africa, is an isopod, physiologically and morphologically, well adapted to terrestrial life with its respiratory organs [51], its water balance, and its resistance to temperature [52, 53]. However, based solely on these adaptations, the species could not exist in the current biotopes. His great success is due, firstly, to his behavioral adaptations—his social character [44, 54] and his orientation [55]—and secondly to his reproductive strategy: *H. reaumurii* as *H. klugii* is semelparous and reproduces during a very short time of the year, April and May for the first species and

In the case of Tunisia, *H. reaumurii* can occupy the same xeric habitat as many other Oniscidea such as *Porcellio* species. In this genus, several studies have been conducted only on widely distributed and very frequent species. These studies focused on morphology [21, 56, 57], reproductive cycles [28, 40, 41, 58], enzymatic polymorphism [59], and Infection with the

Knowledge about the xeric species of *Porcellio* is still limited to their systematic [61–64], and only partial information is available on their reproductive and behavioral strategies

feminizing *Wolbachia* bacterium [60]. Little is known about xeric species.

April for the second [44, 45].

During the last 30 years, great efforts have been made to understand the role of isopods as well as other invertebrates in soil processes and their interactions with the abiotic factors of soil function. These isopods are involved in the process of maintaining soil fertility. They are both "litter transformers" and "ecosystem engineers" [1]. First, these detritivores, like other invertebrates such as Myriapoda and Collembola, contribute to nutrient cycling through mechanical breakdown of plant litter, through biochemical changes in organic matter during digestive transit, and by regulating soil microbial activity [13]. Second, these ecosystem engineers as many other arthropods affect the structural properties of soils ensuring adequate nutrient retention, aeration, and water-holding capacity below ground, facilitate root penetration, and prevent surface crusting and erosion of topsoil. However, most of the studies concerning the contribution of isopods to nutrient cycling have focused on soils in mesic habitats of temperate regions [13–15]. In drier warmer areas of the world, particular attention was addressed to termites and ants as well as to their constructions which affect soil processes by increasing soil porosity and infiltration, reducing or increasing bulk density, altering soil erosion by depositing subsoil on the surface, and altering the concentration and spatial distribution of soil nutrients [1, 16]. Among desert isopods, the role of the burrowing species *Hemilepistus reaumurii* in maintaining soil fertility in arid regions has been well studied. The results of field observations and feeding experiments in the laboratory show that annual ingestion was 3–12% of the available dead organic matter [17] and soil turnover 2–41 g m−2 depending on the soil type and site conditions [1]. *H. reaumurii* by ingestion and defecation of organic matter and inorganic soil particles alters the structure of the decomposition substrate and increase the rate of decomposition in the desert ecosystem [17].

Besides their importance in maintaining ecosystem integrity, woodlice represent a remarkable group of crustaceans due to their high degree of terrestrialization [18]. These Oniscidae originally arising from the aquatic environment became terrestrial during the second half of the Paleozoic era [19]. They have evolved into a wide diversity of terrestrial species that have successfully colonized a wide range of habitats ranging from supralittoral levels (*Ligia* [20]) to mountains (*Porcellio djahizi* [21]) and desert ecosystems [22–24].

According to Sutton et al. [25], the successful colonization of the entire terrestrial globe by Oniscidea is explained by their flexible reproduction (onset and duration of the reproduction period) and its demographic parameters (longevity, age at sexual maturity, number of brood, etc.) that help them overcome the influence of the biotic and abiotic environmental factors to which they are subjected. Temperature, precipitation regime, and photoperiod are important factors regulating the reproduction of terrestrial isopods [26, 27], resulting in temporal coincidences of the release of the mancae with favorable conditions for growth and survival. This could explain the different reproductive patterns observed in terrestrial isopods: the majority of tropical and subtropical species have continuous reproduction [28–30], while temperate has a seasonal breeding followed by a period of sexual rest. The information available on terrestrial isopod reproduction patterns in temperate regions is largely for species occupying mesic habitats [31–42]. The reproductive phenology of xeric species in temperate regions has been studied extensively only for populations in the Middle East desert [32, 43–45]. These desert species that are well adapted to an arid environment differ considerably in their breeding seasons and strategies [46]. The burrowing species *Hemilepistus reaumurii* and *Hemilepistus klugii* are semelparous and reproduce during a very short time of the year: April and May for *H. reaumurii* and April for *H. klugii*. The other xeric species, which do not live in the burrows, are iteroparous. These are *Porcellio ficulneus* and *Porcellio barroisi*, which breed in spring, and *Armadillo albomarginatus*, which breeds in autumn. Both *Porcellio olivieri* and *Agabiformius obtusus* show continuous reproduction under laboratory conditions. Reproductive success in these terrestrial isopods depends on the largest size and number of offspring a female may have. The females of terrestrial isopods produce eggs and develop, following a parturial molt, a marsupium, which is not only a pouch for carrying eggs but plays the same role as a uterus that provides a transfer of substances between the female and its brood [47]. These activities require high energy costs for its offspring [48] that limit the future reproductive potential of the female. Given these constraints, better reproductive success can be achieved by extending care to offspring. Investing in already expensive offspring may be a better choice [44]. This hypothesis seems to explain the high parental investment of some terrestrial isopods in arid regions. The semelparous and burrowing species *H. reaumurii* shows two-parental care with sustainable family cohesion [2]. Indeed, the parental energy investment continues for several months after mancae release, until the young isopods disperse.

Acari, and Collembola [1]. The oniscoids (Oniscidea) with more than 3600 species belonging to 5 major taxonomic groups—Diplocheta, Tylida, Microcheta, Synocheta, and Crinocheta [2]—are an important component. Isopod species composition and diversity were studied in several habitats within the Mediterranean region. Terrestrial isopod community structure differs across habitat types (natural area, seminatural area, agroecosystems, and protected area),

During the last 30 years, great efforts have been made to understand the role of isopods as well as other invertebrates in soil processes and their interactions with the abiotic factors of soil function. These isopods are involved in the process of maintaining soil fertility. They are both "litter transformers" and "ecosystem engineers" [1]. First, these detritivores, like other invertebrates such as Myriapoda and Collembola, contribute to nutrient cycling through mechanical breakdown of plant litter, through biochemical changes in organic matter during digestive transit, and by regulating soil microbial activity [13]. Second, these ecosystem engineers as many other arthropods affect the structural properties of soils ensuring adequate nutrient retention, aeration, and water-holding capacity below ground, facilitate root penetration, and prevent surface crusting and erosion of topsoil. However, most of the studies concerning the contribution of isopods to nutrient cycling have focused on soils in mesic habitats of temperate regions [13–15]. In drier warmer areas of the world, particular attention was addressed to termites and ants as well as to their constructions which affect soil processes by increasing soil porosity and infiltration, reducing or increasing bulk density, altering soil erosion by depositing subsoil on the surface, and altering the concentration and spatial distribution of soil nutrients [1, 16]. Among desert isopods, the role of the burrowing species *Hemilepistus reaumurii* in maintaining soil fertility in arid regions has been well studied. The results of field observations and feeding experiments in the laboratory show that annual ingestion was 3–12% of the available dead organic matter [17] and soil turnover 2–41 g m−2 depending on the soil type and site conditions [1]. *H. reaumurii* by ingestion and defecation of organic matter and inorganic soil particles alters the structure of the decomposition substrate and increase the rate of decomposition in the desert ecosystem [17]. Besides their importance in maintaining ecosystem integrity, woodlice represent a remarkable group of crustaceans due to their high degree of terrestrialization [18]. These Oniscidae originally arising from the aquatic environment became terrestrial during the second half of the Paleozoic era [19]. They have evolved into a wide diversity of terrestrial species that have successfully colonized a wide range of habitats ranging from supralittoral levels (*Ligia* [20]) to

vegetation structure, and altitude [3–12].

30 Community and Global Ecology of Deserts

mountains (*Porcellio djahizi* [21]) and desert ecosystems [22–24].

According to Sutton et al. [25], the successful colonization of the entire terrestrial globe by Oniscidea is explained by their flexible reproduction (onset and duration of the reproduction period) and its demographic parameters (longevity, age at sexual maturity, number of brood, etc.) that help them overcome the influence of the biotic and abiotic environmental factors to which they are subjected. Temperature, precipitation regime, and photoperiod are important factors regulating the reproduction of terrestrial isopods [26, 27], resulting in temporal coincidences of the release of the mancae with favorable conditions for growth and survival. This could explain the different reproductive patterns observed in terrestrial isopods: the majority of tropical and subtropical species have continuous reproduction [28–30], while temperate has Oniscoids have succeeded, thanks to a number of adaptations noted above, to become the only large group of crustaceans to be completely terrestrial. Among them, Species that do not have effective protection against desiccation have been restricted to mesic habitats [49]. However, other species have managed to colonize semiarid and arid habitats, and some have even managed to thrive in the desert. These adaptations have made the nine species of *Hemilepistus* the most abundant detritivores of the macrofauna of many arid areas of Asia Minor [26, 45, 50]. All of them are burrowing species. The model species *H. reaumurii*, widely distributed in North Africa, is an isopod, physiologically and morphologically, well adapted to terrestrial life with its respiratory organs [51], its water balance, and its resistance to temperature [52, 53]. However, based solely on these adaptations, the species could not exist in the current biotopes. His great success is due, firstly, to his behavioral adaptations—his social character [44, 54] and his orientation [55]—and secondly to his reproductive strategy: *H. reaumurii* as *H. klugii* is semelparous and reproduces during a very short time of the year, April and May for the first species and April for the second [44, 45].

In the case of Tunisia, *H. reaumurii* can occupy the same xeric habitat as many other Oniscidea such as *Porcellio* species. In this genus, several studies have been conducted only on widely distributed and very frequent species. These studies focused on morphology [21, 56, 57], reproductive cycles [28, 40, 41, 58], enzymatic polymorphism [59], and Infection with the feminizing *Wolbachia* bacterium [60]. Little is known about xeric species.

Knowledge about the xeric species of *Porcellio* is still limited to their systematic [61–64], and only partial information is available on their reproductive and behavioral strategies [44]. Based on the results obtained by the different studies carried out on the reproductive phenology of the desert species of the Middle East and based on the knowledge acquired in the *H. reaumurii* model terrestrial species, it is envisaged:

extend south of the Tunisian Dorsal from Sfax to Douiret in Tataouine. The climate of pre-Saharan Tunisia is located in the Mediterranean isoclimatic zone which can be defined, from an ecological point of view, as a climate of temperate zone, thus with seasonal and daily photoperiodism and with rainfall concentrated during the cold or relatively cold season (less than

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This great ecosystem diversity has allowed the installation of several species of terrestrial Isopods, and the most recent assessments point to more than 40 species of oniscoids (Charfi-Cheikhrouha et al., unpublished). The *Porcellio* list, assessed by Medini-Bouaziz as 12 species in 2002 (*P. laevis*, *P. variabilis*, *P. dominici*, *P. marginenotatus*, *P. spatulatus*, *P. albicornis*, *P. lamellatus*, *P. djahizi*, *P. simulator*, *P. buddelundi*, *P. olivieri*, and *P. albinus*), was enlarged by the discovery of a 13th species *Porcellio wagneri*, which was first reported in Tunisia by Hamaied et al. (unpublished). The high species richness of *Porcellio* is reached in arid bioclimatic stages (eight species). The xeric species are quite numerous, representing more than a third of all *Porcellio* reported in Tunisia. These pre-desert and desert species belong to two distinct geographical groups of *Porcellio*: the North African group or laevis group and the group bético-rifain or group Hoffmanseggi. The former is represented by four of the five species reported in Tunisia (*P. simulator*, *P. olivieri*, *P. albicornis*, and *P. albinus*) and the last

200 mm/year), summer being dry [64].

one by species *P. buddelundi* [64].

**Figure 2.** Geographical distribution of *Porcellio buddelundi* in Tunisia.

