Exotic Habitats Research Articles

Native Consumers and Seed Limitation Constrain the Restoration of a Native Perennial Grass in Exotic Habitats

Abstract Native consumers and seed limitation may be particularly important in the restoration of native plants where they have been displaced by exotic plants. We used experimental exclosures and seed additions to examine the role of native mammalian consumers and seeding density (500 or 1,000 seeds/m2) in affecting the establishment of a native perennial grass, Purple needlegrass (Nassella pulchra), in the grasslands of California. To focus solely on consumers and propagule density, experimental areas were tilled and weeded. Consumers were important determinants of restoration success: averaged across propagule density, consumers reduced N. pulchra seedling recruitment by nearly 30%, reduced seedling height by 44%, reduced plant establishment by 52%, and reduced reproductive tiller length by 43%. Small rodents affected seedling establishment, especially where seeding density was high but did not affect seedling height. Plots accessible by squirrels and rabbits exhibited significantly decreased seedling height and plant establishment, whereas there was no additional impact of allowing large consumers (i.e., deer) access. Despite strong, spatially variable effects of consumers, doubling seed density led to nearly doubled N. pulchra establishment on average. Consumer effects were persistent, shaping N. pulchra abundance in the subsequent growing season and remaining evident over 18 months after the experiment was initiated. Our work suggests that, despite strong consumer effects, seed addition may be a viable strategy for restoration of N. pulchra in invaded areas where it has been displaced by exotic plants, especially when combined with restoration strategies that reduce competition with exotic plants.

AGE, HABITAT, AND YEARLY VARIATION IN THE DIET OF A GENERALIST INSECTIVORE, THE SOUTHWESTERN WILLOW FLYCATCHER

Characterizing avian diet is complex, especially for generalist insectivores, as food resources can vary over space and time, and individuals of different sexes and ages may consume different food. We examined diet of a generalist insectivore, the Southwestern Willow Flycatcher (Empidonax traillii extimus), at Roosevelt Lake in central Arizona from 2000 to 2004, determined from 344 fecal samples. We found that five prey categories accounted for 70% of the proportional abundance in flycatcher diet: Hymenoptera, Diptera, Cicadellidae, Coleoptera, and Formicidae, although the relative amounts of these and other taxa differed significantly among years. We detected no differences in diet between sexes of adults, but adults and nestlings differed, with higher proportions of Hymenoptera in adult samples and more Diptera in nestling samples. Using a subset of samples, we compared flycatcher diet in habitat patches dominated by native cottonwood (Populus fremontii) and willow (Salix gooddingii), exotic salt cedar (Tamarix ramosissima), or a mix of these tree species. We found that prey groups varied significantly among habitats in only one year, 2002, with Araneae, Lepidoptera, and Odonata significant indicators of native habitat, Cicadellidae and Hymenoptera significant indicators of exotic habitats, and Homoptera a significant indicator of mixed habitat. In 2002, a severe drought resulted in reduced prey base and near total reproductive failure, but we detected no major shift in the composition of adult diet during that year, suggesting that for generalists like the Southwestern Willow Flycatcher, overall insect abundance may be a more important driver of productivity than abundance of specific prey taxa.

Temporal variation in the arthropod community of desert riparian habitats with varying amounts of saltcedar ( Tamarix ramosissima)

We used Malaise traps to examine the aerial arthropod community in riparian habitats dominated by native willow, exotic saltcedar, or a mixture of these two tree species in central Arizona, USA. Over the course of three sampling periods per year in 2003 and 2004, native habitats had significantly greater diversity (Shannon–Wiener) and supported different arthropod communities compared to exotic habitats, while mixed habitats were intermediate in terms of diversity and supported an arthropod community statistically indistinguishable from the exotic site. The composition of arthropod communities varied significantly between the two years, and there was an approximately two-fold difference in richness and diversity. Overall, we documented complex interactions indicating that differences among the arthropod communities of riparian habitats may be driven not only by the composition of native and exotic tree species making up these habitats, but also by year and season of arthropod sampling.

Breakdown of the species-area relationship in exotic but not in native forest patches

We studied the pattern of bird species richness in native and exotic forest patches in Hungary. We hypothesized that species-area relationship will depend on forest naturalness, and on the habitat specialization of bird species. Therefore, we expected strong species-area relationship in native forest patches and forest bird species, and weaker relationship in exotic forest patches containing generalist species. We censused breeding passerine bird communities three times in 13 forest patches with only native tree species, and 14 with only exotic trees in Eastern Hungary in 2003. Although most bird species (92%) of the total of 41 species occurred in both exotic and native forests, the species-area relationship was significant for forest specialist, but not for generalist species in the native forests. No relationship between bird species and area was found for either species group in the forest with exotic tree species. The comparison of native versus exotic forest patches of similar sizes revealed that only large (>100 ha) native forests harbor higher bird species richness than exotic forests for the forest specialist bird species. There is no difference between small and medium forest patches and in richness of generalist species. Thus, the species-area relationship may diminish in archipelago of exotic habitat patches and/or for habitat generalist species; this result supports the warning that the extension of exotic habitats have been significantly contributing to the decline of natural community patterns.

Non-native plantation forests as alternative habitat for native forest beetles in a heavily modified landscape

The once extensive native forests of New Zealand’s central North Island are heavily fragmented, and the scattered remnants are now surrounded by a matrix of exotic pastoral grasslands and Pinus radiata plantation forests. The importance of these exotic habitats for native biodiversity is poorly understood. This study examines the utilisation of exotic plantation forests by native beetles in a heavily modified landscape. The diversity of selected beetle taxa was compared at multiple distances across edge gradients between each of the six possible combinations of adjacent pastoral, plantation, clearfell and native forest land-use types. Estimated species richness (Michaelis–Menten) was greater in production habitats than native forest; however this was largely due to the absence of exotic species in native forest. Beetle relative abundance was highest in clearfell-harvested areas, mainly due to colonisation by open-habitat, disturbance-adapted species. More importantly, though, of all the non-native habitats sampled, beetle species composition in mature P. radiata was most similar to native forest. Understanding the influence of key environmental factors and stand level management is important for enhancing biodiversity values within the landscape. Native habitat proximity was the most significant environmental correlate of beetle community composition, highlighting the importance of retaining native remnants within plantation landscapes. The proportion of exotic beetles was consistently low in mature plantation stands, however it increased in pasture sites at increasing distances from native forest. These results suggest that exotic plantation forests may provide important alternative habitat for native forest beetles in landscapes with a low proportion of native forest cover.

A Toad More Traveled: The Heterogeneous Invasion Dynamics of Cane Toads in Australia

To predict the spread of invasive species, we need to understand the mechanisms that underlie their range expansion. Assuming random diffusion through homogeneous environments, invasions are expected to progress at a constant rate. However, environmental heterogeneity is expected to alter diffusion rates, especially by slowing invasions as populations encounter suboptimal environmental conditions. Here, we examine how environmental and landscape factors affect the local invasion speeds of cane toads (Chaunus [Bufo] marinus) in Australia. Using high-resolution cane toad data, we demonstrate heterogeneous regional invasion dynamics that include both decelerating and accelerating range expansions. Toad invasion speed increased in regions characterized by high temperatures, heterogeneous topography, low elevations, dense road networks, and high patch connectivity. Regional increases in the toad invasion rate might be caused by environmental conditions that facilitate toad reproduction and movement, by the evolution of long-distance dispersal ability, or by some combination of these factors. In any case, theoretical predictions that neglect environmental influences on dispersal at multiple spatial scales may prove to be inaccurate. Early predictions of cane toad range expansion rates that assumed constant diffusion across homogeneous landscapes already have been proved wrong. Future attempts to predict range dynamics for invasive species should consider heterogeneity in (1) the environmental factors that determine dispersal rates and (2) the mobility of invasive populations because dispersal-relevant traits can evolve in exotic habitats. As an invasive species spreads, it is likely to encounter conditions that influence dispersal rates via one or both of these mechanisms.

The invasive round goby Apollonia melanostoma (Actinopterygii: Gobiidae) - a new intermediate host of the trematode Neochasmus umbellus (Trematoda: Cryptogonimidae) in Lake Erie, Ohio, USA

The invasive round goby Apollonia melanostoma (Actinopterygii: Gobiidae) - a new intermediate host of the trematode Neochasmus umbellus (Trematoda: Cryptogonimidae) in Lake Erie, Ohio, USA

Pollination Ecology and Seed Production of Rhododendron Ponticum in Native and Exotic Habitats

Alien plants may be reproductively limited in exotic habitats because of a lack of mutualistic pollinators. However, if plants are adequately served by generalist pollinators, successful reproduction, naturalisation and expansion into exotic habitats may occur. Rhododendron ponticum is very successful, ecologically damaging invasive plant in Britain and Ireland, but is in decline in its native Iberian habitat. It spreads locally by sending out lateral branches, but for longer distance dispersal it relies on sexually produced seeds. Little is known about R. ponticum's pollination ecology and breeding biology in invaded habitats. We examined the flower-visiting communities and maternal reproductive success of R. ponticum in native populations in southern Spain and in exotic ones in Ireland. R. ponticum in flowers are visited by various generalist (polylectic) pollinator species in both native and exotic habitats. Although different species visited flowers in Ireland and Spain, the flower visitation rate was not significantly different. Insects foraging on R. ponticum in Spain carried less R. ponticum pollen than their Irish counterparts, and carried fewer pollen types. Fruit production per inflorescence varied greatly within all populations but was significantly correlated with visitation at the population level. Nectar was significantly depleted by insects in some exotic populations, suggesting that this invasive species is providing a floral resource for native insects in some parts of Ireland. The generality of the pollination system may be factor contributing to R.ponticum's success in exotic habitats.

A conceptual framework for comparing species assemblages in native and exotic habitats

Exotic (nonnative) species are known to have a wide variety of impacts on native biota. One potential set of impacts that have been poorly studied are the effects of replacing native habitat‐providing species with exotic ones, e.g. when native trees that compose a woodland are replaced by an exotic tree plantation. Here we develop a graphical model that can be used to explore how multiple taxonomic components (such as birds, mammals and plants) respond to such changes. We suggest that four categorical responses are possible, with respect to changes in species richness (or other quantitative measures) of taxonomic groups within species assemblages. First, that each taxonomic group compared between habitats will be relatively unchanged, e.g. have equivalent values of species richness. Second, that a decrease (for example in species richness) of one group will be compensated for by an increase (in species richness) of another group. Third, that one or more groups will decrease without any compensated increases in other groups. Fourth, that one or more groups will increase without any compensated decreases in other groups. We provide empirical support for 3 of these 4 responses, with respect to measures of species richness, with much evidence for equivalency between habitats. These types of comparisons should provide a valuable tool for evaluating 1) the efficacy of environmental mitigation efforts that artificially create or restore habitats and 2) the types of changes that have occurred over time or across space as native habitat‐producing species are replaced by exotic ones. Finally, this conceptual framework should help to broaden the range of possible changes considered by ecologists who study the impacts of exotic species.

Age structure and growth of the woody legume weed Cytisus scoparius in native and exotic habitats: implications for control

Summary To be successful, integrated weed management (IWM) requires sufficient knowledge of the ecology of the weed and the invaded system to allow prediction of the outcome of control efforts. We studied the age and size structure of both native and exotic populations of Scotch broom Cytisus scoparius to test predictions regarding why it is invasive in exotic habitats and, consequently, to determine management priorities. Particular emphasis was given to the efficient selection of biological control agents. A minimum of 30 plants was harvested per site in Europe (seven sites), New Zealand (20 sites) and Australia (11 sites). Age, determined by counting annual growth rings, stem diameter and height were recorded for each plant. The area cleared was recorded to calculate plant population density. Stem diameter and height were significantly correlated with age, but there was considerable variation in size for any given age and no major differences were apparent between the growth rates of plants from native and exotic populations. This may be because population densities of exotic stands were significantly higher than native stands, and intraspecific competition has previously been demonstrated to limit plant growth. The age structures of many populations were described by regressions between loge(number of plants m−2) and loge(age). However, the proportion of populations described by this regression varied significantly between countries and was highest in Australia and lowest in Europe. Departure from this relationship was most common at roadside sites and recently cleared commercial forestry plantations, indicating that large‐scale artificial disturbance can promote pulses of seedling establishment. Disturbance‐related establishment was found to be most common in Europe, indicating that large‐scale disturbance is unlikely to explain increased weediness in exotic habitats. The maximum age of plants sampled did not vary between native and exotic habitats, indicating that, as for the related weed Ulex europaeus, increased longevity of exotic plants is unlikely to explain why exotic populations are weedier than native populations. Significantly higher population densities recorded in exotic habitats may be a consequence of a paucity of specialist insect herbivores. Such higher density populations are more likely to exclude competing vegetation so, in the absence of major disturbance, exotic broom stands are more likely to regenerate than European populations, and therefore to persist for generations. Synthesis and applications. The data support the hypothesis that natural enemies regulate native populations of Scotch broom and, consequently, that invasive exotic populations are suitable targets for biological control. Agents should be sought that (i) reduce plant fecundity and therefore seedling densities and (ii) defoliate established plants, enabling competing vegetation to establish beneath stands and reduce seedling survival. These results are potentially applicable to other invasive introduced legume shrubs.

Development of an ecological mapping methodology for urban areas in New Zealand

At present there is no ecologically based mapping system designed for application to urban areas in New Zealand. New Zealand’s ecological structure is particularly interesting as it combines indigenous habitats comprising significant numbers of endemic species with a vibrant imported ecology comprising habitats characteristic of their primarily European and Australian origins. In New Zealand, the focus to date in habitat mapping has been on developing vegetation mapping techniques for application to predominantly indigenous habitats in rural areas. Thus, they omit reference to the type of mixed exotic-indigenous vegetation associated with habitats common to urban areas, such as cliff faces, disused quarries, private gardens and grounds, river and rail corridors. A project was undertaken in conjunction with the Dunedin City Council to develop a habitat map of the city. The aim was to produce a map that would accommodate the diverse highly modified habitats characteristic of Dunedin and that would incorporate all types of urban open space ranging from indigenous habitats, such as forest to exotic habitats such as lawns, and residential gardens. The project developed a land use and habitat classification hierarchy applicable to the New Zealand urban context, including a classification system for private gardens. This paper describes the classification system that was developed, its benefits, limitations and application. The map is the first attempt to record all natural land uses, including gardens in any New Zealand city at a detailed level, i.e. at a scale of 1:3000. In all 1100 separate habitat parcels were mapped. The map revealed that whilst Dunedin is a city rich in natural vegetation very little of this is indigenous or even predominantly indigenous vegetation. A Geographic Information System was used to map the urban habitats and store the habitat data. The habitat map and associated data will be used by the council in developing an open space strategy for the city.

Death assemblages of molluscs on St Martin's Flats, Isles of Scilly: a surrogate for regional biodiversity?

We test the hypothesis that the biodiversity of the death assemblage of shelled molluscs (gastropods and bivalves) on a single sandflat is representative of the biodiversity of the regional living fauna from the complete spectrum of habitat types, and can therefore be used as a surrogate for the purposes of rapid biodiversity assessment. Two biodiversity indices considered appropriate for such an assessment are average taxonomic distinctness (Δ+) and the variation in taxonomic distinctness (Λ+), which are, respectively, measures of the degree to which the species are taxonomically related to each other (i.e. the average taxonomic spread), and the degree to which taxa are over or under represented (i.e. the evenness of the distribution across the taxonomic tree). In each case, measured values were compared with the regional living species pool using a randomisation test. Collections and identifications of shells were made by both a non-expert in mollusc taxonomy and by taxonomic experts, the latter using microscopic examination of sediment samples as well as simple surface searches for macro-species. In all studies, Δ+ for the gastropods in the death assemblage was fully representative of the regional living fauna, but for bivalves it was significantly lower. This is because most of the bivalves were characteristic of the sandflat habitat, which introduced a bias, whereas post-mortem transport of gastropods, characterising exotic habitats, is more random. For gastropods, in all studies but one, Λ+ was significantly higher than expected from a random sample of the regional species pool, and for bivalves this was the case for all studies, suggesting the over-representation of some taxa and the under-representation of others. For the total shelled molluscan fauna (gastropods + bivalves) all Δ+ values were below, and all Λ+ values above, expectation. Results obtained by experts and a non-expert in mollusc taxonomy did not differ. In general, death assemblages at a single location are only likely to be representative of a wider region if there is randomisation as a result of post-mortem transport processes.

Domesday, here at last!

‘Ecotourism’ usually conjures up such images as jungle treks to far away places. However, natives of the UK no longer need to travel abroad to ‘ecotour’: some of the most exotic habitats are now available on their doorstep. The showpiece of the Eden Project, situated in a disused clay pit in Cornwall (SW England), comprises two geodesic domes (‘biomes’) that are home to plants – and many animals – from warm and tropical regions. It is hoped that the collection will not only help to conserve and preserve endangered species, but also act as a valuable resource for research, education and the pure, unadulterated delight of looking at plants. [http://www.edenproject.com/] NC

The invertebrate fauna on broom, Cytisus scoparius,in two native and two exotic habitats

This study quantifies the invertebrate fauna found on broom, Cytisus scoparius, L. (Link), in two countries where it grows as a native plant (France and England) and two countries where it grows as an alien plant (New Zealand and Australia). The data are used to test three hypotheses concerning the predicted differences in invertebrate community structure in native versus exotic habitats: (1) Are generalist phytophages dominant in exotic habitats and specialist phytophages dominant in native habitats? (2) Are there empty phytophage niches in exotic habitats? (3) As a plant species accumulates phytophages, do these in turn accumulate natural enemies? The broom fauna was sampled at five sites in each country by beating five broom bushes per site. The sampling efficiency of beating was quantified at one field site and it was shown to collect 87 % of invertebrate abundance, 95 % of invertebrate biomass and 100 % of phytophagous species found on the branches. Generalist phytophages were dominant on broom in exotic habitats and specialists dominant on broom in the native habitats. Thus, the two countries where broom grows as a native plant had higher numbers of total phytophage species and a higher abundance of specialist phytophages per bush. There was no significant difference in the average abundance of generalist phytophage species found per bush in native and alien habitats. Phytophages were assigned to seven feeding niches: suckers, root feeders, external chewers, flower feeders, seed feeders, miners and pollen feeders. Empty niches were found in the exotic habitats; species exploiting structurally specific parts of the host plant, such as flowers and seeds, were absent in the countries where broom grows as an alien plant. The pattern of niche occupancy was similar between native and exotic habitats when just the generalist phytophages were considered. As phytophage abundance and biomass increased, there were concomitant increases in natural enemy abundance and biomass. Thus, it appears that as plants accumulate phytophages, the phytophages in turn accumulate natural enemies and a food web develops around the plant. Moreover, in the native countries, the history of association between the natural enemies and their prey has been sufficient for specialist predators and parasitoids, feeding on the specialist phytophages, to have evolved.

Cyzenis albicans(Diptera: Tachinidae) Does Not Prevent the Outbreak of Winter Moth (Lepidoptera: Geometridae) in Birch Stands and Blueberry Plots on the Lower Mainland of British Columbia

In the late 1980s, a new outbreak of the introduced winter moth, Operophtera brumata (L.), occurred in Richmond, on the lower mainland of British Columbia. This was accompanied by the introduced parasitoid, Cyzenis albicans (Fallen). Populations were monitored at 2 birch woodlands and 2 blueberry plots between 1989 and 1993. Parasitism by C. albicans and predation by generalist predators were important mortality factors during the outbreak. Predation of moth pupae increased at all sites between 1989 and 1990. Parasitism by C. albicans caused significant mortality each year reaching a maximum in 1991 and remaining high through to 1993 at birch sites. The winter moth populations collapsed simultaneously in 1992 at all study sites, despite different levels of parasitism and 2 very different host plants. As the outbreak collapsed at Richmond, the moth continued to increase in numbers and cause severe defoliation of birch at new sites in southern Vancouver where parasitism remained low. C. albicans is unable to prevent the initial outbreak of winter moth even when the 2 species are introduced simultaneously. The parasitoid requires high density host populations before becoming well established, but may contribute sufficient additional mortality to prevent subsequent prolonged outbreaks. The control of high density winter moth populations in North America by C. albicans supports the hypothesis that natural enemies that are rare in their native habitat will be effective control agents when released into exotic habitats without competitors or their own natural enemies.

Breeding Ecology and Behavior of the Hawaiian Hawk

We studied the ecology of the endangered Hawaiian Hawk (Buteo solitarius) on the island of Hawaii for three breeding seasons. Their breeding strategy is a prime example of a K-selected species characteristic of many birds in tropical environments: clutch size was one and brood-rearing was among the longest reported for any diurnal raptor. Twenty-eight nests were found in a variety of native and exotic habitats. Incubation lasted 38 days, nestlings fledged after 59-63 days, and parents cared for fledglings for an average of 30.2 weeks, which was 2.5 to 10 times longer than similar-size temperate zone raptors. Males assisted females with incubation, but only females brooded young. Radio-tagged juveniles remained within 0.63 km of their nests for the first two months after fledging, after which dispersal distances expanded gradually. Avian (45%) and mammalian (54%) prey dominated the diet of nestlings. There was no evidence that avian malaria, introduced predators, or environmental contaminants were affecting their population. Based upon estimates of population size, the availability of suitable nesting habitat, and reproductive success, we suggest the species be considered for downlisting from endangered to threatened status.

French Colonial Film before and after Itto: From Berber Myth to Race War

French cinema's wave washed over the colonies as well as the metropole, and filmmakers were soon carting their cameras off to remote corners of the empire to record exotic habitats and peoples for display to audiences at home. Colonial staffs and film crews cooperated in making the documentaries, gravitating toward each other as cobearers of the civilizing mission. Narrative fictional film shot on location in the colonies, cinema's other first wave, arrived in 1921 with LAtlantide. Its million-dollar budget, surreal plot, hypnotic Saharan scenery, and intrepid Foreign Legion heroes caused a sensation at its Paris premiere. Filming on location became de rigueur, and the visionary proconsul of Morocco, Marechal Louis-Hubert Lyautey, who founded the protectorate in 1912, put its resources at the disposal of French directors. By providing them with logistical support and schooling them in the realities of Moroccan society and culture, he supported a trend in French film toward authenticity and verisimilitude that gave it an advantage over Hollywood back-lot productions. Quick to see film's potential for capturing the public imagination and promoting his agenda, he sponsored films that encouraged mutual respect between cultures. Lyautey's star waned after he failed to anticipate or cope with the Rif uprising of 1925-26, and cinetma colonial found new sponsors in settler-dominated

Biological Control of Scotch Broom: Modelling the Determinants of Abundance and the Potential Impact of Introduced Insect Herbivores

Simulation and analytical models are developed for the European shrub Scotch broom Cytisus scoparius Link (Fabaceae). The simulation model is spatially explicit and allows us to explore not only changes in population size but also the proportion of ground covered by the weed. The simulation model incorporates spatially local density-dependent competition, asymmetric competition between seedlings and established plants, a seed bank, local seed dispersal and an age-structured established plant population. This model is designed to incorporate much of the known population biology of broom. The analytical models are simple approximations of the simulation. The basic model contains nine parameters: the probability a site is disturbed, p dist ; the probability a seed becomes a seedling, g; the probability a seedling survives the first year, s; the probability a seed is lost from the seed bank, d; the minimum age for reproduction, A min ; maximum plant age, A max ; seed production per site, F; the probability a seed is retained in the parental site, fh; and the probability a site becomes suitable for colonization after broom senesces, p so . We review published data on the demography of broom from studies around the world, and also present some previously unpublished data. These data suggest that broom in some exotic habitats can achieve higher fecundities and live longer than in its native range. Analytical approximations provide a good description of the simulation results over a wide range of biologically reasonable parameter values. Specifically, the analytical modekls work well when plants are long-lived or highly fecund. Analysis of the models indicates that when broom colonizes all suitable sites with probability one, that the fraction of sites occupied by broom is determined by only three parameters: the probability of disturbance, p dist the probability a site becomes suitable for colonization following plant senescence, p so ; and maximum longevity, A max . In exotic habitats, where individual broom plants can produce several thousand seeds, differences in these parameters are the most likely reason why broom populations are more weedy than in the native range. The impact of insect herbivores, which reduce plant fecundity, on broom abundance is explored for several environmental scenarios. This analysis suggests that potential biological control agents are most likely to have a substantial impact if the disturbance rate is high, plant fecundity is low, and seedling survival is low. Even herbivores that reduce seed production by only 75% can have a dramatic impact on broom abundance, in contrast to several published predictions. Extensions to the models to allow for arbitrary patterns of age-dependent senescence, and site-specific probabilities of disturbance are presented.

Fertility control of mammal pests and the conservation of endangered marsupials.

Populations are bounded by negative feedbacks operating through fertility or mortality, termed population regulation. If fertility is artificially reduced, the average size of the population is also reduced, but only under certain conditions. If (i) juvenile survival or (ii) adult survival improve due to lower fertility, or (iii) territoriality limits populations, the effects of lower birth rate will not change population size unless such reduction exceeds the effects of these processes. Published data on population trends and birth rates have allowed a comparison among species of instantaneous rates of change. The intrinsic rate of increase, rm, and population variability are both related to body size, because birth rates and survivorship are also related to body size. These rates are trade-offs as adaptations. Populations of species in exotic habitats may fluctuate more than when they are in their indigenous habitats. Fertility control could reduce such fluctations. Marsupials have lower birth rates than eutherians, and so rely more on survivorship, perhaps as an adaptation to unpredictable environments. Compromising survival by either habitat change or increased predation will affect marsupials more than eutherians. This explains why many marsupial populations are declining towards extinction.

Survival of Arbuscular Mycorrhizal Fungi Following Reciprocal Transplanting Across the Great Basin, USA

Mycorrhizal fungi are transplanted into exotic habitats to aid in agriculture and land restoration. However, different taxa have different effects on hosts, and little is known about their survival or spread. The fate of arbuscular mycorrhizal fungi was examined in a reciprocal transplant experiment of a single host shrub species, Artemisia tridentata subspecies tridentata between two semiarid sites. The sites were located near Reno, Nevada, and San Diego, California, in the western United States. The experiment was a complete factorial design: two plant populations, A. tridentata ssp. tridentata from the Reno and the San Diego sites, and five fungal treatments (Acaulospora elegans from San Diego, Scutellospora calospora from Reno, a whole‐soil inoculum from San Diego, a whole‐soil inoculum from Reno, and uninoculated soil). Based on fluorescein isothiocyanate‐labeled antiserum studies, neither fungus declined over three growing seasons at the site of origin with the plant population of origin. Survival of the fungi always declined in association with the exotic host population and at the exotic site. Spore density of fungi that had been inoculated was generally very low. However, when significant differences between treatments were observed, spore density of the fungus was higher in association with plants that had been inoculated with it than with uninoculated plants, and the fungus had higher survivorship in the site and with the host of its origin. Both fungi usually sporulated more often under inoculated than uninoculated host plants. Over three growing seasons, both A. elegans and S. calospora survived in their sites of origin and in the exotic location with both plant populations. The fungi spread throughout the root systems and between plants of the different treatments. These results show that, while there was higher survival by the arbuscular mycorrhizal fungi at the site and with the host of origin, these fungi survived and spread for at least three growing seasons, although they declined significantly at the exotic site and with exotic hosts.