Dispersal Habitat Research Articles

The species pool concept applied to forests in a fragmented landscape: dispersal limitation versus habitat limitation

The species pool concept has been used as a theo- retical framework for understanding local community rich- ness. A significant problem in putting the concept into practice is the lack of methods for determining the size of the species pool. We tested the hypothesis that species composition of recent forests is primarily determined by the species composi- tion of neighbouring older forests against the null-hypothesis that species are a random sample of the species occurring in the study area. Forest plant species composition of recently established fragments was significantly correlated with spe- cies composition in neighbouring older forests (i.e. the local species pool). When older forest within a neighbourhood of 1000m radius is considered, seed dispersal sources can be found for 91% of the flora in the recent forests. For an individual fragment, dispersal is a much more important deter- minant of species presence than the environment, with an average of 46% of the total pool excluded from local pools by dispersal limitation and only 8% excluded by environmental limitations. The species richness of recent forests is on aver- age 23% of the local species pool. Several hypotheses are proposed for this low percentage, such as asymmetric compe- tition due to the early successional state or the limited coloni- zation period.

MIGRANT STOPOVER AND POSTFLEDGING DISPERSAL AT A MONTANE FOREST SITE IN VERMONT

To investigate the use of high elevation fir forests by fall passage migrants, we conducted standardized mist-netting and banding at a 1150-1175 m elevation site on Mt. Mansfield in north-central Vermont during the autumns of 1995-1997. Overall, we captured 3024 individuals of 62 species in 10,048 cumulative net hours (30.1 birds/100 net hr). We divided species into 3 classes: (1) those breeding regularly on Mt. Mansfield above 916 m elevation (16 species), (2) those breeding only sporadically or at very low densities above 916 m (6 species), and (3) those occurring only as transients (40 species). Breeding species accounted for 68% of new captures, followed by transients (22%), and sporadic/low density breeders (10%). Of the ten most abundant species captured, only two, Black-throated Blue Warbler (Dendroica caerulescens)and Ovenbird (Seiurus au- rocapillus), were transients, accounting for 50% and 9%, respectively, of all transient captures. Hatching-year birds accounted for 94% of known-age transients and 81% of known-age individuals among locally breeding species. Recapture rates of transients were extremely low (0.3%), while recapture rates among species known to breed locally (including presumed transient individuals) were higher (2.2%). Nearly 75% of all birds captured were very lean at first capture, and only 26% of recaptured individuals increased their fat scores between first and final captures. Weight changes of recaptured birds varied: 48% lost weight, 44% gained weight, and 8% maintained the same weight between first and final captures. Our data suggest that conditions on the Mt. Mans- field ridgeline are not conducive to prolonged migratory stopovers and that most migrants may be unable to meet their energetic requirements for continued migration. However, we believe that montane forest habitats may be preferentially selected by those migrants that use them for breeding. We further believe that montane fir forests may be an important postfledging dispersal habitat for Black-throated Blue Warblers and other low or mid-elevation breeding species, and that conservation planning for montane forest sites should carefully consider the needs of migrants outside the breeding season. Received 18 March 1999, accepted 25 Oct. 1999. Of the numerous demands that migrant birds face during their annual migrations, se- lection of enroute stopover habitat is para- mount. Choice of stopover habitat may play a pivotal role in determining a migrant's surviv- al and is dependent both on intrinsic suitabil- ity of the habitat and on extrinsic factors such as weather, time constraints, energetic condi- tion, and availability of the habitat (Hutto 1985, Moore and Simons 1992). Stopover mi- grants must resolve potentially conflicting needs to meet their energy demands, avoid predation, adjust to unfamiliar habitats, com- pete with other migrants and residents, and deal with unfavorable weather conditions (Moore et al. 1995). Loss or degradation of

Managing Boreal Forest Landscapes for Flying Squirrels

Flying squirrel (Pteromys volans) populations have declined severely during the past few decades, and the species has beconme afocal species in forest management and the conservation debate in Finland. We compared land.scape structure around known flying squirrel home ranges with randomly chosen forest sites to determine which landscape patterns characterize the areas occupied by the species in northern Finland. We sought to identify the key characteristics of the landscape that support the remaining flying squirrel popu- lations. We analyzed landscape structure within circular areas with 1- and 3-knm radii around 63 forest sites occupied by flying sqtuirrels, and arotund 96 random sites. We applied stepwise analysis of the landscape structure where landscapes were built ul) step-by-step by adding patch types in order of their suitability for the flying squirret The land-use and forest-resource data for the analysis were derived from multisource na- tional forest inventory and imported to a geographical information systenm. Landscape patch types were di- vided into three suitability categories. breeding habitat (mixed spruce-deci.duous forests); dispersal habitat (pine atd young forests); and unsuitable habitat (young sapling stands, open habitats, water). Flying squir- rel landscapes contained more suitable breeding habitat patches and were better connected by dispersal hab- itats than random1 landscapes. Our results suggest that for the persistence of the flying squirrel, forest manag- ers should 1) maintain a deciduous mixtutre, particularly in spruce-dominatedforests; 2) maintain physical connectivity between optimal breeding habitats; and 3) impose coarse-grained structures on northeastern Finnish landscapes at cturrent levels of habitat availability.

A control program for an outbreak of the scorpion Tityus serrulatus, Lutz and Mello 1922 in the town of Aparecida, São Paulo state (Scorpiones, Buthidae)

A scorpion control program was proposed for the town of Aparecida (SP), an endemic region of Tityus serrulatus. Clusters of scorpions in urban and rural areas, environmental degradation of the town's outskirts and new scorpion procreation and dispersal habitats were studied. In addition, infrastructure problems such as the disposal and collection of residential and municipal refuse, sanitation (sewage and storm sewer), condition of vacant lots and constructions in the urban area were evaluated. After an epidemiological study, educational measures such as the distribution of pamphlets, cleaning group work, visits to residences and cooperation from High School teachers and students were also suggested. Chemical control was indicated in high-risk sites, especially those of near-school buildings. Furthermore, the use of natural predators was also mentioned within the present sanitation regulations for urban areas. The authors assert that these procedures must be integrated and continued uninterruptedly for several years. They also suggest a collaborative work with those responsible for the dengue eradication program, as well as the institution of the "scorpion study week", which would greatly contribute to the education of the population, to preventive programs and to scorpion control.

Explosive Breeding Aggregations and Parachuting in a Neotropical Frog, Agalychnis saltator (Hylidae)

Agalychnis saltator gathers in spectacular breeding aggregations on lianas above temporary swamps. Both males and females descend to breeding aggregations by parachuting and return rapidly to the canopy by hand-over-hand locomotion up lianas. Amplecting males are no different in size from single males, and the sizes of males and females in amplexus are not correlated. Unusual characteristics of this species compared to congeners include egg-laying during daylight hours and laying grey eggs that are packed into moss on lianas. Sources of egg mortality include desiccation, submergence in water, and predation by ants, snakes, and birds. Parachuting and walking may both be efficient locomotor modes that enable frogs to live in the dispersed habitat of the canopy and yet gather in a short amount of time for explosive breeding at isolated ponds.

Genetic Divergence among Populations of the Yellow-Bellied Slider Turtle (Pseudemys scripta) Separated by Aquatic and Terrestrial Habitats

Allelic variation at 18 loci is described for Pseudemys scripta (N = 367) livetrapped from 12 populations, representing three habitat types separated by different types of intervening habitat (terrestrial vs aquatic). Of the 18 loci examined 13 were polymorphic. Mean heterozygosity was 0.131. Significant allele frequency differences were observed among the 12 populations. Patterns of allelic differentiation and overall genetic divergence among populations were not consistent across habitat types. Populations from aquatically separated habitats had significantly higher heterozygosities than did populations from terrestrially separated habitat and showed less interpopulation genetic distance/unit distance. However, genetic similarities among populations appear to be a function of geographic proximity, regardless of the intervening habitat and potential for dispersal and interpopulation gene flow.

Carabid Beetles in Lush Forest Patches on the Aland Islands, South-West Finland: An Island-Mainland Comparison

We collected carabid beetles with pitfall traps in patches of lush coniferous forest on five small islands (3-4 km off the shore) and in five similar sites on the mainland on the Aland Islands, south-west Finland, with identical sampling effort in each site. Four times more individuals were caught on the mainland than on the islands (1069 v. 245). Species number was also greater on the mainland (25 v. 18); however, when sample sizes were standardized by rare- faction, species numbers did not differ significantly. Striking differences were observed in species composition and abundances between the mainland and the islands; the dominant species of the mainland (Patrobus atrorufus, > 50% of the total mainland sample) was represented in the island samples by only two in- dividuals, and several other abundant mainland species were scarce on the islands as well. Two species (Cychrus caraboides and Pterostichus niger) were more abundant on the islands than on the mainland. Relative differences in community structure were smaller among the mainland sampling sites than among the island sampling sites. 'Passive sampling' is an inadequate model for the colonization of the island habitat patches by carabid beetles. Factors that probably affect the colonization process include environmental differences, especially differences in the composition of habitats in the surroundings of the sampling sites, and aute- cological characteristics of the species, such as dispersal ability and habitat pre- ferences.

Song variation in insular and mainland California Brown Creepers(Certhia familiaris)

Songs of Brown-Creepers(Certhia familiaris) in California were studied. Each individual usually sang one theme. Two geographic groups of songs were described which were designated the northern and southern dialects. These songs differed in the morphology of the introductory and terminal syllables. The northern dialect is currently known to extend from Point Reyes to the City of San Francisco, and includes birds from east San Francisco Bay. The southern dialect ranges from Carmel and Point Lobos to Morro Bay. Birds from the Hastings Reservation, 30 miles inland, sang the southern dialect. Creepers on Angel Island exhibited the “typical” island phenomenon of simpler structure but greater individual variability. We suggested that lack of social interaction due to dispersed habitat has contributed to these song changes. California Creeper songs are more variable with regard to note sequencing than those of their European congeners.