Variations saisonnières des appendiculaires de la région nord Adriatique

Appendicularians from 140 hauls made in the north Adriatic area, over a period of 9 months, have been examined. A high population density, with 67 specimens per cubic meter and a low specific diversity with 10 species is described. Three species: Oikopleura dioica, O. longicauda and O. fusiformis represent more than 95% of the specimens collected. The presence of a West-East gradient in the population density is shown, along with a correlation with the influence of the Pô inflow. A study of the seasonal variations of the three main species shows that all the characteristics of the Western region are very favourable to O. dioica. This fact seems to be the clue to the qualitative and quantitative variations of the appendicularian population in this area.     

Predator-prey interactions between the larvacean Oikopleura dioica and bacterioplankton in enclosed water columns

The larvacean Oikopleura dioica Fol was fed ³H-labeled natural assemblages of marine bacterioplankton. Grazing rates ranged from <1 to >100 ml day^-1 individual^-1 and were highly dependent onlarvacean body size. These rates were combined with estimates of abundance of O. dioica in large floating enclosures with semi-natural populations (Controlled Ecosystems Populations Experiment, CEPEX) to determine the impact of the larvacean on the bacterial populations and to estimate the amount of bacteria ingested by the larvaceans. Apparently, O. dioica has minimal influence on the population dynamics of the free-living bacteria, although bacteria may form a substantial portion of the larvacean's diet.     

Convergent development of ecological,genetic, and morphological traits in native supercolonies of the red ant Myrmica rubra

Ant supercolonies (large networks of interconnected nests) represent the most extreme form of multi-queen breeding (polygyny) and have been found across ant lineages, usually in specific long-term stable populations. Many studies on the genetic population structure and demography of ant supercolonies have been done in recent decades, but they have lacked multicolonial control patches with separated colonies headed by a single or few queens so the origin of the supercolonial trait syndrome has remained enigmatic. Here, we set out to compare sympatric supercolonial and multicolonial patches in two natural Danish populations of the common red ant Myrmica rubra. We used DNA microsatellites to reconstruct genetic colony/population structure and obtained morphological and density measurements to estimate life history and ecology covariates. We found that supercolonies in both populations completely dominated their patches whereas colonies in multicolonial patches coexisted with other ant species. Supercolony patches had very low genetic differentiation between nests, negligible relatedness within nests, and lower inbreeding than multicolonial patches, but there were no significant morphological differences. One population also had nests that approached true outbred monogyny with larger workers and males but smaller queens than in the two other social nest types. Our results suggest that once smaller colonies start to adopt additional queens, they also gain the potential to ultimately become supercolonial when the habitat allows rapid expansion through nest budding. This is relevant for understanding obligate polygyny in ants and for appreciating how and why introduced North American populations of M. rubra have recently become invasive.     

Vertical distribution,population structure and life cycles of four oncaeid copepods in the Oyashio region,western subarctic Pacific

Vertical distribution and population structure of four dominant oncaeid copepods (Triconia borealis, Triconia canadensis, Oncaea grossa and Oncaea parila) were investigated in the Oyashio region, western subarctic Pacific. Seasonal samples were collected with 0.06 mm mesh nets from five discrete layers between the surface and 2,000 m depth at seven occasions (March, May, June, August and October 2002, December 2003 and February 2004). The depth of occurrence of major populations of each species differed by species; the surface–250 m for T. borealis, 250–1,000 m for T. canadensis, 250–500 m for O. grossa and 500–1,000 m for O. parila. The ontogenetic vertical migration characterized by deeper occurrence of early and late copepodid stages, and shallower occurrence of middle copepodid stages was observed in T. canadensis and O. parila. Of the four oncaeid copepods, almost all copepodid stages occurred throughout the study period, suggesting that their reproduction continues throughout the year in the region. Nevertheless, a clear developmental sequence of stage-to-stage was traced for T. canadensis and O. grossa copepodids, implying their generation time to be 1 year. For T. borealis and O. parila copepodids, no clear seasonal succession was observed thus estimation of their generation time was uncertain. The present comprehensive results of vertical distribution and life cycle features for T. borealis, T. canadensis, O. grossa and O. parila are compared with the few published data on oncaeid species distributing in high latitude seas.     

Modelling dispersal with diffusion and habitat selection: Analytical results for highly fragmented landscapes

Quantifying dispersal is crucial both for understanding ecological population dynamics, and for gaining insight into factors that affect the genetic structure of populations. The role of dispersal becomes pronounced in highly fragmented landscapes inhabited by spatially structured populations. We consider a landscape consisting of a set of habitat patches surrounded by unsuitable matrix, and model dispersal by assuming that the individuals follow a random walk with parameters that may be specific to the habitat type. We allow for spatial variation in patch quality, and account for edge-mediated behavior, the latter meaning that the individuals bias their movement towards the patches when close to an edge between a patch and the matrix. We employ a diffusion approximation of the random walk model to derive analytical expressions for various characteristics of the dispersal process. For example, we derive formulae for the time that an individual is expected to spend in its current patch i, and for the time that it will spend in the matrix, both conditional on the individual hitting next a given patch j before hitting any of the other patches or dying. The analytical formulae are based on the assumptions that the landscape is infinitely large, that the patches are circularly shaped, and that the patches are small compared to interpatch distances. We evaluate the effect of these assumptions by comparing the analytical results to numerical results in a real patch network that violates all of the three assumptions. We then consider a landscape that fulfills the assumptions, and show that in this case the analytical results are in a very good agreement with the numerical results. The results obtained here allow the construction of computationally efficient dispersal models that can be used as components of metapopulation models.     

Les appendiculaires du Golfe du Bengale

Appendicularians from 76 hauls made from June to August 1964 in the Bay of Bengal, aboard the R. V. “Kistna”, have been examined. Of the 26 species determined, 10 are new for the Bay of Bengal and, amongst these, 2 were unknown in the Indian Ocean. The composition of the group formed by the most abundant and most frequent species is characteristic of the fauna of the Indian Ocean. Oikopleura longicauda represents 50% of the total number of individuals collected, followed by O. rujescens 14%, Megalocerus huxleyi 8%, O. fusiformis and Fritillaria borealis f. sargassi 6%, O. cophocerca and Stegosoma magnum 2%. No other species reached 1%. The density of the species in the occidental zone deereased fairly regularly with latitude: 21 species in the south, then going on towards the north, 14, 11 and 2. In the area south of the strait of Malacca only 5 species were found, in its opening into the Bay of Bengal, 18. The Oikopleuridae were present in all the hauls, but the Fritillaridae were absent from 25. The geographical distribution of each species has been studied. Oikopleura longicauda is the only one which is clearly more abundant in the north; most of the other species show a decreasing gradient from south to north. The characteristic difference between the different zones cannot be established from the hydrological data (temperature and salinity). It seems, therefore, that the indigenous species are not very common, and that others originate from the Indian Ocean, transported by the south-north currents present at that time of year.     

Influence of temperature changes on oxygen uptake and ammonia and phosphate excretion,in relation to body size and weight,in Oikopleura dioica (Appendicularia)

The relationship between the rates of oxygen consumption, ammonia and phosphate excretion of a pelagic tunicate, the larvacean Oikopleura dioica Fol, 1872 were assessed as a function of size, dry weight and ash-free dry weight at 15°, 20° and 24°C. O. dioica has higher respiration and excretion rates than copepods of similar weight, but the weight exponent of the allometric power function: Y=aX ^b is similar to that of other poikilotherms. Temperatures above 20°C have a depressing effect on respiration and ammonia excretion. 90% of the variance in metabolic rates is explainable by body mass and temperatures Q₁₀ values for oxygen consumption, ammonia and phosphate excretion, respectively, are 2.45, 1.86 and 1.75 between 15° and 20°C, and 3.75, 2.90 and 3.60 between 20° and 24°C. Metabolic quotients (O:N, O:P, N:P) indicate a protein-oriented diet. The results of this study suggest weak metabolic regulation in O. dioica, an energetic strategy which allows an immediate response to favourable changes in feeding conditions.     

Die verbreitung der kaltwasser- und der warmwasserfauna der Appendicularien im nördlichen Nordatlantischen Ozean im Spätwinter und Spätsommer 1958

The Appendicularia caught in vertical hauls during the cruises of R.V. “Anton Dohrn” and R.V. “Gauß” in the northern North Atlantic Ocean, in late winter and late summer of the International Geophysical Year (I.G.Y.), 1958, were investigated. In addition, material caught during spring, 1955 by R.V. “Anton Dohrn” was used (Figs. 1 and 2; Tables 1 and 2). Seasonal differences are revealed in the appendicularian fauna in the open ocean between 40° and 65° northern latitude. Among the species caught (Table 2) in 1955, northwest of the Hebrides, Pelagopleura australis Bückmann 1923 (Fig. 3) is of special interest. This species has hitherto only been found in antarctic and southern waters; it is, however, possible that Sinistroffia scripsii Tokioka 1957 is a synonym. In the same place, a new form of Fritillaria venusta Lohmann was found, which is described as F. venusta f. replicata n.f. (Fig. 4). The hitherto known form should be named F. venusta f. bicornis. In Figs. 5 to 7, the species dominating in single catches are indicated by symbols. A borderline between the areas of cold-water and warm-water forms can be drawn. This line is located farther to the North in late summer than in late winter. In the eastern part of the area investigated, the difference amounts to 5° latitude. Warm-water species prevail over cold-water species or appear in equal numbers in both seasons in places where water with temperatures above 11°C is found within the upper 100 m (Figs. 8 and 9). It is, however, known that Oikopleura dioica thrives also at temperatures of 10°C and below; this was also found in the spring of 1955. Cold-water species exhibited higher frequencies as well as abundances, in the late summer than in the late winter of 1958. This fact is chiefly due to an increase in individual numbers of the most important boreal species, Oikopleura labradoriensis, but also of the arctic O. vanhoeffeni and the boreal Fritillaria borealis typica. Relative to O. labradoriensis, the population of F. borealis typica decreases in late summer. During spring 1955, both species exceeded the 1958 values by far. This is considered to be the result of annual, rather than seasonal, differences. The composition of the warm water fauna (Tables 4 and 5) reveals considerable seasonal differences. In late winter, O. longicauda is the most abundant species; it prevails in almost all warm-water catches. In late summer, it is outweighed by O. dioica and O. fusiformis in the total catch, by O. dioica in many single catches in the whole warm-water area, by O. fusiformis in its north eastern part in a few very rich catches, together with Fritillaria pellucida. For size comparison of the individnals, standard trunk length could not be used because of the generally bad state of preservation. In Oikopleura, the lengths of the left stomach lobe were measured instead. It is, however, to be taken into account that the regression of body length to the stomach length (left side) is different at different stages of maturity. In ripening and ripe individuals, body length increases at a higher rate because of growths in length of the gonads. The regressions were calculated for 3 maturity stages (A, B, C; Figs. 10, 12 and 14) of O. labradoriensis and O. vanhoeffeni. In O. longicauda, the specimens were distinctly smaller during late summer, and the proportion of juveniles (stage A) was much higher (Fig. 11). Possibly, this is caused by a reproduction rate still reduced during late winter, but increasing later in the year. O. labradoriensis shows similar, though less pronounced, differences in the proportion of maturity stages, and no significant differences in size composition (Fig. 13). The 1955 material contains a much higher proportion of mature individuals than either cruise of 1958. Similar conditions as in O. longicauda cannot, therefore, be assumed to be involved in regard to O. labradoriensis, at least not at present. There were more mature O. vanhoeffeni individuals present in spring 1955, but they were much smaller than during late summer 1958. No explanation for this observation can, at present, be offered.     

Population genetic structure of North American <Emphasis Type="Italic">Ophiactis</Emphasis> spp. brittle stars possessing hemoglobin

With the discovery of previously unreported populations of hemoglobin-possessing Ophiactis from the Texas coast in the Gulf of Mexico, an investigation into its population structure, including populations of O. simplex from the Pacific coast of California and O. rubropoda from the Atlantic coast of Florida, was undertaken using DNA sequence data from the mitochondrial COI gene. The reconstructed haplotype network suggests that California populations contain the ancestral source of mtDNA variation, and there is no evidence of recent introductions into Texas. Population genetic analyses reveal the California, Florida, and Texas Ophiactis populations to each be significantly differentiated from one another. Sequence divergence among the three areas is shallower than would be predicted given biogeographic history. Texas and Florida populations are equally genetically diverged from California populations as they are to one another, despite the greater potential for gene flow between these areas. The genetic distinctiveness of the Texas populations and the concordance of this pattern with phylogeographic patterns in other brittle star systems indicate an isolated and independent evolutionary history and we hypothesize that the three geographic regions included in this study each serve as hypotheses of population-level lineages that remain to be tested with independent sources of data.     

Genetic diversity and genetic structure in the brown alga Halidrys dioica (Fucales: Cystoseiraceae) in Southern California

Genetic diversity and genetic structure in a population of the brown seaweed Halidrys dioica Gardner were evaluated in five sites in southern California, USA, in 1991, using isozyme electrophoresis. H. dioica is relatively long-lived and has an outcrossing mating system and floating reproductive fronds with the potential for longdistance gamete dispersal. Because these characteristics are hypothetically important in determining genetic diversity and structure, we predicted that genetic diversity would be high and genetic structure would be exhibited only at relatively large geographic scales in H. dioica populations. The data were consistent with the prediction: genetic diversity (% polymorphic loci, no. of alleles/locus, average expected heterozygosity) was high compared to that of other seaweed species. Genetic structure (Wright's F statistics, Nei's genetic distance, point-pattern analysis of alleles) was low within and among distinct rocky reefs over 4 km of coast but high in subpopulations separated by 90 km. Life-history characteristics may be useful predictors of genetic diversity and structure in seaweed populations, but information on selection regimes, long-distance dispersal, and the extent of clonal propagation, for example, are critically lacking.     

Summer zooplankton distribution in a Georgia Estuary

Zooplankton were collected with Van Dorn bottles at two estuarine stations near Savannah, Georgia, USA, during summer, 1974, from the surface, 2 m, 4 m, and at the bottom of the water column at 2-h intervals for 11 days. Acartia tonsa occurred at the surface at night and during high and rising tides in higher concentrations than at the same depth during daylight and other tide stages. The highest bottom concentrations of this calanoid copepod occurred at high tide. A negative phototaxic response was also apparent in this species. While not quantitatively sampled by Van Dorn bottles, harpacticoid copepods and Pseudodiaptomus coronatus Were distributed in a manner similar to that of A. tonsa. Copepod nauplii, on the other hand, were always more abundant at the surface than at the bottom, with the highest concentration occurring during low tide. The distribution pattern of nauplii appears to be a function of dilution and concentration by tidally induced changes in water volume, whereas more advanced copepod stages follow a complexly controlled distribution pattern linked with tidal mixing dynamics as outlined in a previous study by Jacobs (1968).     

The effect of migration on the viability,dynamics and structure of two coexisting metapopulations

Two species of butterflies, Euphydryas aurinia and Melitaea phoebe, coexist as two metapopulations in a 38-patch network in Hebei Province, China. A Markovian model, whose transition matrix is the product of two matrices which represent the local extinction and recolonization process respectively, is used to describe the metapopulation dynamics. The application of this model to the metapopulation, consisting of 12 local populations in the northern subregion, shows that the expected life times of E. aurinia and M. phoebe are 160 and 121 years respectively and usually nearly half of the patches are occupied by E. aurinia, while only 1–3 patches are occupied by M. phoebe. We claim that E. aurinia can persist for a long time while M. phoebe faces relatively big extinction risk. By comparing the population dynamics with and without migration, we find M. phoebe benefits much more from migration than E. aurinia. Most patches are occupied mainly by local populations for E. aurinia, while by immigrants from the 8th patch for M. phoebe, meaning that E. aurinia has a classical metapopulation structure while M. phoebe has a source–sink metapopulation structure.     

Choosing between darkness and light: The ecological genetics of photic behaviour in the planktonic larva of Spirorbis borealis

The light-dark preference of individual Spirorbis borealis larvae was measured by the relative amount of time spent in the lighted half of a container. Specimens taken from a tidal pool were 20% more photonegative than those obtained outside the pool, probably because of natural selection against being washed out of the pool at high tide. The between-population behavioural difference was maintained in the laboratory, and is genetic in origin. Applying biometrical genetic analysis to larvae grouped into half-sib families, the within-population variation was used to estimate an upper limit to the heritability of 0.36. It is concluded that the differences among populations greatly exceed heritable variation within populations. A numerical selection model based on the estimated maximum heritability suggests, however, that the populations could diverge by 20% in less than a year, in response to local differences in the selection regime.     

The occurrence of Oratosquilla investigatoris (Crustacea: Stomatopoda) in the pelagic zone of the Gulf of Aden and the equatorial western Indian Ocean

Surface swarms of the stomatopod Oratosquilla investigatoris (Lloyd, 1907) were observed in the Gulf of Aden and the equatorial western Indian Ocean during 1967. Collections from inshore and offshore swarms were made in both areas, and from demersal trawl catches in the equatorial area. O. investigatoris was also collected from the stomachs of several species of oceanic pelagic and inshore fish from 1965 to 1967, and was also reported in the stomach contents of the lesser frigate bird. Further collections were made from strandings on two oceanic islands in the equatorial area. Indirect observations on the occurrence of the species resulted from increased predation on pelagic longline baits during seasos of apparent abundance of O. investigatoris in the equatorial region. At the surface, predation by the species was observed on fast-swiming fish, and the swimming behaviour was noted. A size range of 6 to 37 mm carapace length (CL) was recorded for the 4000 specimens collected, and there was no size difference between the sexes. Length-frequency analysis of the samples indicated a major mode at 19 to 21 mm CL and an increase in length of 3 mm over 3 months. The sex ratio was weighted in favour of females in the majority of collections. It was concluded that the pelagic swarming of O. investigatoris is an important ecological phenomenon, but not regular in the area, and the factors affecting it could not be deduced from the available data.     

Male's return rate, rather than territory fidelity and breeding dispersal, explains geographic variation in song sharing in two populations of an oscine passerine (Oreothlypis celata)

Males of some oscine passerines learn and share songs of neighboring males. This process can lead to the formation of song pattern neighborhoods or microhabitat song dialects. The degree to which song sharing occurs between populations and the spatial scale over which neighboring males share songs, however, can vary widely, and interpopulation comparisons have suggested that song sharing is more common in residents than in migrants. Here, we examine two populations of the orange-crowned warbler (Oreothlypis celata) to quantify patterns of song sharing at the northern (long-distance migrant) and southern (short-distance migrant) edges of the breeding distribution and to test if return rate, territory fidelity, and breeding dispersal explain the patterns found in the two populations. The southern population (O. celata sordida breeding on Santa Catalina Island, California; 33°N) had a higher annual return rate to their territories and exhibited higher song sharing in neighborhoods than their counterparts (O. celata celata breeding in Fairbanks, Alaska; 64°N). Year-to-year patterns of territory fidelity and breeding dispersal distances were similar between populations. Our results suggest that if migratory distance generally covaries with the proportion of returning males, this could explain different levels of song sharing between the short- and long-distance migrants.     

Population structure of the black tiger prawn, Penaeus monodon, among western Indian Ocean and western Pacific populations

We examined the population structure of the black tiger prawn, Penaeus monodon Fabricius, 1798, in the Indo-West Pacific by analyzing the geographic distribution of elongation factor 1-alpha intron sequences from specimens collected during the winter and spring of 1997. Both the molecular phylogeny of alleles and F-statistics indicated very strong differentiation between populations from the western Indian Ocean and western Pacific. This pattern is concordant with other recent studies of marine species in this region, implying that the Indo-Australian Archipelago represents a biogeographic break between populations in the Indo-West Pacific. F _ST-values among populations in the western Indian Ocean also indicate structure within this region, whereas no structure was found among western Pacific populations. Nucleotide diversity was significantly lower in the western Indian Ocean populations than in the western Pacific, implying that the populations have regional differences in demographic history. Received: 16 November 1998 / Accepted: 26 May 1999     

A process-based population dynamics model to explore target and non-target impacts of a biological control agent

The risks and benefits associated with efforts to control invasive alien species using classical biological control are being subjected to increasing scrutiny. A process-based population dynamics model was developed to explore the interactions between a folivorous biological control agent, Cleopus japonicus, and its plant host Buddleja davidii. The model revealed that climate could have a significant impact upon the interactions between B. davidii and C. japonicus. At the coolest sites, the impact of C. japonicus on B. davidii was slowed, but it was still eventually capable of controlling populations of B. davidii. At the warmer sites where both B. davidii and C. japonicus grew faster, B. davidii succumbed rapidly to weevil damage. We hypothesise that barring an encounter with a natural enemy, C. japonicus will eventually be able to provide sustained control B. davidii throughout the North Island of New Zealand. The model scenarios illustrate the potential for the C. japonicus population to attain high densities rapidly, and to defoliate patches of B. davidii, creating the potential for spill-over feeding on non-target plants. The potential magnitude of this threat will depend partly on the climate suitability for C. japonicus, the pattern by which it migrates in response to a reduction in the available leaf resource, and the suitability of non-target plants as hosts. In all migration scenarios considered, the pattern of population growth and resource consumption by C. japonicus was exponential, with a strong tendency toward complete utilisation of resource patches more quickly at the warmer compared to colder sites. In addition to providing some useful hypotheses about the effects of climate on the biological control system, and the non-target risks, it also provides some insight into the mechanisms by which climate affects the system.     

Mitochondrial phylogeography of the killifish Aphanius fasciatus (Teleostei, Cyprinodontidae) reveals highly divergent Mediterranean populations

We studied the genetic structure of the Mediterranean killifish Aphanius fasciatus. Analysis of the sequence variation in a 372-bp portion of the mitochondrial control region in 623 fish from 27 sampling sites along the species’ distributional range (Tyrrhenian coast, Sardinia, Sicily, Adriatic coast, Malta, Tunisia, and Greece) yielded 120 distinct haplotypes. Most of the haplotypes are unique, and only 15 % are shared among different populations. The high F _ST value (=0.80) suggests a strong population genetic structuring. The phylogenetic analysis based on Bayesian inference, maximum likelihood and maximum parsimony, and the median-joining network show a sharp separation of the Southeastern Sicilian populations (belonging to the Hyblean region) and of the fluvial Tunisian population of Rio Melah from the others. The Adriatic, the Eastern Sicilian, and the Greek populations are well differentiated, while the group of populations from the Central-Western Mediterranean does not show a clear pattern of differentiation. Our findings indicate that the current genetic structuring of A. fasciatus reflects historical geographical patterns occurring within the Mediterranean basin from the Late Miocene to the Pleistocene. The presence of divergent evolutionary entities in the Hyblean region and the Tunisian Rio Melah supports their inclusion as target areas for the conservation of A. fasciatus.     

The food of four species of pleuronectiform larvae in the eastern English Channel and southern North Sea

An examination was made of the stomach contents of the larvae of the plaice Pleuronectes platessa Linnaeus, 1758; the flounder Platichthys flesus (Linnaeus, 1758), the dab Limanda limanda (Linnaeus, 1758), and the sole Solea solea (Linnaeus, 1758) collected in the eastern English Channel and in the Southern Bight during the winter and spring of 1971. These 4 species of flat fish have distinct diets, and competition for food between them is largely avoided. Plaice larvae fed almost exclusively on Oikopleura dioica; flounder larvae also ate O. dioica, but in addition a wide range of planktonic organisms including phytoplankton, polychaete larvae, lamellibranch larvae, and copepod nauplii. Dab larvae fed mainly on the nauplii and copepodite stages of a variety of copepods, but particularly of Temora longicornis. Some T. longicornis copepodites and polychaete larvae were eaten by sole larvae, but the principal prey of these was lamellibranch larvae. The larvae of all the species began to feed in the yolk-sac stage; the initial food of all except plaice consisted of dino-flagellates, followed by tintinnids and copepod nauplii. Feeding began at dawn and the number of feeding fish and the number of food organisms in their stomachs increased throughout the day to a maximum near sunset. There were no consistent differences between the two areas in the diets of any of the species.     

Simulating population variation and movement within fragmented landscapes: An application to the gopher tortoise (Gopherus polyphemus)

As the human activity footprint grows, land-use decisions play an increasing role in determining the future of plant and animal species. Studies have shown that urban and agricultural development cannot only harm species populations directly through habitat destruction, but also by destroying the corridors that connect habitat patches and populations within a metapopulation. Without these pathways, populations can encounter inbreeding depression and degeneration, which can increase death rates and lower rates of reproduction. This article describes the development and application of the FRAGGLE model, a spatial system dynamics model designed to calculate connectivity indices among populations. FRAGGLE can help planners and managers identify the relative contribution of populations associated with habitat patches to future populations in those patches, taking into account the importance of interstitial land to migration success. The model is applied to the gopher tortoise (Gopherus polyphemus), a threatened species whose southeastern U.S. distribution has diminished significantly within its native range due to agricultural and urban development over the last several decades. This model is parameterized with life history and movement traits of the gopher tortoise in order to simulate population demographics and spatial distribution within an area in west-central Georgia that supports a significant tortoise population. The implications of this simulation modeling effort are demonstrated using simple landscape representations and a hypothetical on land-use management scenario. Our findings show that development resulting in even limited habitat losses (10%) may lead to significant increases in fragmentation as measured by a loss in the rate of dispersions (31%) among area subpopulations.