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Theories Dealing with the Ecology of Landbirds on Islands
Abstract
This chapter discusses notable contributions to the knowledge of the ecology of island landbirds, mainly in the northern hemisphere along with the research on Galapagos finches and landbirds on Australian islands. The protocol for future ecological studies of island landbirds is presented. Interspecific competition represents interactions between species for any shared resource likely to be in limited supply. The diversity of resources available is usually considered less on islands than on mainland areas. The degree of saturation of an island landbird fauna refers to the extent to which an island is stocked with landbird species relative to the area of the island and the variety of resources that it offers. Coupled with this last concept are two processes: how often do species of landbirds immigrate to islands and once there, how frequently do populations become extinct. The chapter discusses the frequency of the change in the composition of the breeding landbird fauna of a particular island changes.
... However z-values are also dependent on elevation, and archipelago distance from the mainland (Wright 1981), should they be correlated with area. The effect of area on species richness is generally more substantial for islands further from the mainland (Abbott 1980), although occasionally the opposite has applied for birds (Schoener 1976). This concept is intuitively illustrated in the original theory of island biogeography (p. ...
... The two variables, although similar in nature, therefore designate different relationships with species richness. Abbott (1980) discusses the differences between plant diversity and habitat diversity as predictors. The negative correlation between geological diversity and small mammal species richness supports the presumption that more complex systems are less invasible, although geological diversity is only just significant, and the relationship between geological diversity and floral complexity is only assumed, not tested. ...
... Area and elevation were found to be most significant, but it was concluded that the islands were under "non-equilibrium" status. Abbott (1980) It should be noted that because detrending the avian species richness estimates may have removed some natural variability, the values used for exotic landbird species richness are the raw estimates. To partial out the bias of sampling effort the number of cards returned, and the number of grid squares an island covers, are included as explanatory variables. ...
... Some of this discussion has centred on turnover rates in avifauna on islands and the methods of evaluating these rates (Diamond 1969(Diamond , 1971Power 1972;Terborgh and Faaborg 1973;Hunt and Hunt 1974;Lynch and Johnson 1974;Jones and Diamond 1976;Diamond and May 1977;McCoy 1982) and particularly regarding the interpretation of what constitutes a 'natural' immigration or extinction (see Lynch and Johnson; Jones and Diamond for discussion of these points). Abbott (1980) summarized the basic viewpoints current in ecological studies of landbirds on islands. Those relevant to changes in species composition are: MacArthur and Wilson's (1967) view that immigrations and extinctions of landbird species on islands are frequent for most species, resulting in frequent changes in the composition of breeding landbird populations; Lack's (1969Lack's ( , 1971Lack's ( , 1976 view that immigrations and extinctions are very frequent, as is turnover in breeding species; Diamond's (1969Diamond's ( , 1970aDiamond's ( , 1970bDiamond's ( , 1975 view that immigrations and extinctions are infrequent for most species, but frequent for a few, which results in turnover being very frequent; 0310-7833/85/030467$02.00 and Abbott's (1978Abbott's ( , 1980 view that for islands round Australia and New Zealand, immigrations and extinctions are infrequent and turnover of breeding species is also infrequent. ...
... Abbott (1980) summarized the basic viewpoints current in ecological studies of landbirds on islands. Those relevant to changes in species composition are: MacArthur and Wilson's (1967) view that immigrations and extinctions of landbird species on islands are frequent for most species, resulting in frequent changes in the composition of breeding landbird populations; Lack's (1969Lack's ( , 1971Lack's ( , 1976 view that immigrations and extinctions are very frequent, as is turnover in breeding species; Diamond's (1969Diamond's ( , 1970aDiamond's ( , 1970bDiamond's ( , 1975 view that immigrations and extinctions are infrequent for most species, but frequent for a few, which results in turnover being very frequent; 0310-7833/85/030467$02.00 and Abbott's (1978Abbott's ( , 1980 view that for islands round Australia and New Zealand, immigrations and extinctions are infrequent and turnover of breeding species is also infrequent. Abbott maintains that water acts as a substantial bamer to the movement of landbirds onto islands (as does Diamond) but that most potential immigrants do reach islands occasionaily. ...
... Our results for Rottnest I. give an average of 0.12, nearly a fifth of the lowest figure for the Channel Is. Our results for Rottnest I. support the view put forward by Abbott (1978Abbott ( , 1980) that for Australian islands, immigrations and extinctions are infrequent and turnover of breeding species is also infrequent. ...
The avifauna of Rottnest Island, W.A., has been surveyed four times between 1904 and 1983: by Lawson
in 1904, Glauert (1928), Storr between 1953 and 1962, and ourselves between 1981 and 1983. There were
three recorded extinctions and 10 immigrations in the 79-year period, but none of the extinctions and only
three of the immigrations could be regarded as valid for calculating natural turnover rates. The remainder
had been influenced by human activity; therefore the avifauna extinction rate for Rottnest Island was 0,
the immigration rate was 0.04% per year for non-marine species of bird and the relative turnover rate for
the 79 years was 0.12% per year. These results for Rottnest I. support the view of Abbott (1978, 1980)
that for Australian islands, immigrations and extinctions are infrequent and turnover of breeding species
is also infrequent. There have been 109 sightings of vagrants recorded for the island between 1905 and 1983;
only one of these had individuals present in sufficient numbers during the breeding season to establish a
breeding population. The data show that for one Australian island natural extinctions of both passerines
and non-passerines are rare. Water does act as a barrier and although birds do cross water and often appear
as vagrants, they very rarely do so in sufficient numbers or at the right time to establish breeding populations.
... The rationale which follows from the niche theory and the dynamic equilibrium theory is that island habitats are saturated with fewer species than mainland ones with the resuit that extra-resources become available for more conspecifics. Several other hypothèses have been proposed to explain larger population densities, including reduced prédation (Higuchi 1976, Abbott 1980, Nilsson et al. 1985, Williamson 1981, and reduced dispersai, the so-called "fence effect" (MacArthur et al. 1972b, Tamarin 1977. Reduced prédation may also resuit in a release in habitat sélection because camouflage is less important in the absence of predators, favouring niche expansion in suboptimal habitats. ...
... Reduced prédation may also resuit in a release in habitat sélection because camouflage is less important in the absence of predators, favouring niche expansion in suboptimal habitats. Unfortunately, very few rigorous attempts have been made to test thèse hypothèses (Abbott 1980, George 1987, including the hypothesis of a causal relationship between species richness and population density. One exception has been provided by George (1987) who experimentally demonstrated that higher densities of small land birds on the Coronados islands, Mexico, resulted from lower prédation rates than on the nearby mainland. ...
This paper reviews ecological and evolutionary processes that operate among and within insular communities, species and populations. Being basically non-evolutionary the MacArthur and Wilson's paradigm of island biogeography holds well in explaining processes that operate on the short ecological time, and proved to be helpful in explaining such issues as colonisation-extinction processes, species richness at equilibrium and species turnover. But several limitations make it insufficient as a modern tool for explaining evolutionary changes on islands. Colonising an island necessarily entails rapid evolutionary changes as a response to both non-selective and selective evolution. This results in a cascade of changes of life history traits, the so-called insular syndrome. Components of this syndrome include changes in morphology (size and shape), demography (age-specific fecundity, survival, dispersal) and behaviour. Shifts in behaviour are among the most spectacular features in insular vertebrates. Surprisingly few systematic and broad-scale analyses of demographic changes on islands have been designed to document the classical tenet of evolutionary shifts from high reproductive rates and short life span towards the opposite combination of life history traits as a result of high intraspecific competition in crowded insular populations. Examples of shifts in life history traits are given from a detailed case study on the biology of Blue tits in the island of Corsica, and most of these changes fit the predictions of an insular syndrome. An interesting trend resulting from shift from dispersal to sedentariness and habitat fidelity in islands is the potential for population differentiation at much smaller spatial scales than on mainland regions. This results in enhancing within-species diversity which counterbalances the species impoverishment of insular biotas. Although ecological adjustments and evolutionary changes make insular communities self-regulating assemblages of species that are resistant face to the risks of spontaneous extinction and invasion, insular communities are among the most vulnerable biota on Earth. The most important threats to island birds are discussed and some directions are given for promoting studies that could contribute to fill the most important gaps in our knowledge on evolution on islands and contribute to conservation issues.
... Niche shifts, such as increasing niche breadth in foraging strata and substrate, are considered an evolutionary adaptation to changes in food availability (Abbott et al. 1977, in Abbott 1980Blondel 1985;Grant 1998;Kleindorfer et al. 2006), suggesting that food abundance is greater on KI than in MLR. In this study we did not measure size or abundance of prey, so are unable to compare niche shifts in relation to food availability. ...
... bill and tarsus) and adaptation to local environmental conditions (such as vegetation structure) by the process of natural selection. For example, increased tarsal length may allow more efficient foraging on a wider variety of substrates (Grant 1965(Grant , 1971, and longer bills may allow the intake of a greater range or size of food items (Grant 1965;Abbott 1974aAbbott , 1980, an adaptation to generalist foraging in the absence or reduction of interspecific competition , or an adaptation to increased size of food items (Abbott 1977). In this study we found that island fairy-wrens had significantly longer tarsi and foraged on a wider variety of substrates than their mainland counterparts. ...
Understanding patterns of adaptive divergence is a cornerstone for understanding the process of speciation. The theory of ecological speciation predicts that natural selection shapes adaptive divergence. In this observational study, we examined the first phase of ecological speciation, namely adaptive divergence in foraging behaviour and morphology across populations (island and mainland sites) of the sexually dimorphic Superb Fairy-wren (Malurus cyaneus) that have been separated for approximately 9000 years. Current island theory predicts larger body-size in island species, as well as more generalist foraging and occupation of a wider ecological niche that is favoured by large body-size. We examined the vegetation structure across replicate study areas on Kangaroo Island and the mainland Mount Lofty Ranges in South Australia and found significant differences in vegetation structure important for Superb Fairy-wrens (percentage bare earth, shrub size and shrub abundance). Compared with mainland birds, island birds of both sexes: (1) occupied a wider niche breadth; (2) were significantly larger in body-size; and (3) varied less in morphology. Between the sexes: (1) there were few inter-sexual foraging differences; (2) males had a larger body-size and bill-length at both island and mainland locations; and (3) females had larger bill-width and bill-depth at both locations. These findings support the hypothesis of adaptive divergence in this species, with evidence that vegetation structure is important in their foraging behaviour and affects their morphology across locations (niche breadth was potentially favoured by a different interspecific community). The lack of consistent sexual differences in foraging ecology suggests that the patterns of sexual dimorphism may be shaped by reproductive roles rather than vegetation structure in this species. The categorisation of the Kangaroo Island population as a separate subspecies (M. c. ashbyi) is supported by these findings.
... Log-log transformation has been the most common transformation used in the literature to describe the species-area relationship because of its higher explanatory power compared to other types of transformations (Watling and Donnelly 2006 ). In the ETIB, log-log transformed relationship [species (S) – area (A)], log S = log k + z log A, where the z value, corresponding to the slope of the regression line, has been indicated as a coefficient suggesting a biological meaning in respect to the isolation degree of the archipelago (Preston 1962, Connor and McCoy 1979, Abbott 1980). If the islands are isolated, z values might be even larger (Schoener 1976) and indeed have been used to indicate degrees of perceived isolation of the samples for the target group (Kitchener et al. 1980, 1982, East 1981). ...
... Our data widely support this pattern, because chance (i.e. the percentage of unexplained variance) contributed in a more substantial way to the area-species relationship, to its fit and to its z-value for vagrants than for the other assemblages studied (see also Woolhouse 1983 for the study of the effect of chance on bird assemblages in habitat fragments). These arguments on vagrants could be limited to the northern hemisphere , where migrant non-breeding species (i.e., vagrants ) are an important component of landbird faunas (Abbott 1980). ...
Wetlands are naturally patchy habitat types that in fragmented landscapes are usually immersed inside a sea of anthropogenic habitat matrix. Decrease in patch size area and increase of patch isolation are two important components of wetland fragmentation. We investigated the effects of fragment area on bird species richness at four-level assemblages in a highly fragmented Mediterranean wetland system of Central Italy. Our results indicate that fragment area influenced differently the species richness for distinct assemblages in wetland fragments, Area was significantly correlated to total species richness, vagrant, breeding and Phragmites-related breeding species (PBS). A comparison of the various 2 regression equations showed that the log-log relationship was the best-fitted model and the amount of variation (R of log-log regression line) was much higher for PBS and breeders than for vagrants. This pattern confirmed that when including vagrants in studies based on the equilibrium theory of island biogeography, the 'insularity of islands' is reduced. We also found that higher z-values (regression slope) were associated with PBS and breeding birds, supporting the idea of a 'matrix effect' on the studied species.
... The article by Vakhrushev and Rautian (1993) even drew an analogy between the establishment and growth of urban bird populations and the consequences of large-scale biocenotic crises, examples of which are provided by the paleontological record. More obvious are the analogies with one of the main biocenotic principles formulated by Thienemann (1939) and with the concept of population density compensation on oceanic islands, which is supposed to be due to the reduced species richness of these islands compared to similar continental habitats (MacArthur et al., 1972;Abbott, 1980;Faeth, 1984;Wiens, 1989a;etc.). This explanation cannot be considered universal. ...
... The life histories of oceanic island species are shaped by selective pressures which may result in adaptations such as niche expansion as a consequence of release from interspecific competition (Crowell 1962, MacArthur et al. 1972, Abbott 1980, Baker-Gabb 1986, Blondel 2000. Island species are exposed to local stochastic events (e.g. ...
Reliable estimates of life history parameters and their functional role in animal population trajectories are critical, yet often missing, components in conservation and management. We developed seasonal matrix population models of the Red‐tailed Hawk in the upper and lower forests of the Luquillo Mountains, Puerto Rico, to describe the influence of early life stages (nestling and clutch survival) on population growth. Modeled populations exhibited positive discrete rates of growth in forests above 400 m (λ highlands = 1.05) and in forests below 400 m (λ lowlands = 1.27) of the Luquillo Mountains. Further, adult survival was the parameter with the highest proportional effect and direct contribution to the population growth. Besides survival of adults, our results identified that nestling survival had the second greatest influence on λ, stressing the importance of this life stage for the population growth rate of Red‐tailed Hawks in our study area. Seasonal matrices are not commonly used to describe population dynamics of birds. However, these may be a useful tool to analyze the influence of life stages in the annual cycle to better address conservation and management needs, especially for species inhabiting oceanic islands.
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... This is probably because most seabirds have large foraging, wandering and dispersal areas, and the competition for limited resources. It corresponds to the theoretical suggestions that closely related taxa tend to reduce each other and that one generalist of a taxonomic or ecological group tends to replace two or more specialists on islands; small niches are not occupied by a specialist species but covered by a generalist (lAck, 1969;diAmond, 1974;ABBott, 1980). However, all taxonomical ratio values are still higher than those of the South-eastern Pacific Juan Fernandez Islands off Chile (hAhn et al., 2009). ...
Following an isolation gradient in West-Mexico the avifauna of three study areas is investigated, on mainland reserve and two island groups. The avifaunas are described and analysed regarding species richness, environmental attributes, ende-mism, broader ecological niches, and brood status. The taxonomical composition is determined on different hierarchy levels. Most species records come from mainland Chamela (262), followed by the coastal Marias (191) and the oceanic Revilla-gigedos (148). Thereof 139 bird species breed in Chamela, 61 on Marias and only 29 on the Revillagigedos. In total, in the three study areas 364 species were recorded, which belong to 22 orders. On island groups generally less taxa per hierarchy level are present than on the mainland, especially on the remote Revillagigedos. Here, on average 1.7 species are found per genus, 2.2 genera per family, and 2.5 families per order. In the analysis of the taxonomical hierarchy relations to each other an isolation gradient is identified: from mainland Chamela via the coastal Marias to the oceanic Revillagigedos the degree of relatedness decreases on average. The results support the theoretical hypothesis that on islands closely related taxa tend to exclude each other and that one generalist tends to replace several specialists. Small ecological niches are often not occupied by specialist species on islands, but are used by generalists.
... This is the rationale for using island distributions to assess conservation suitability of mainland tracts of different sizes. Yet forest islands are not exactly like oceanic islands, and inferring processes from oceanic island distributional data is rarely convincing (Abbott, 1980). Species lists for potential forest reserves would be a sounder basis for conservation decisions than would lists for island analogs. ...
We quantify the notion of predictable species loss from progressively smaller islands, and apply the quantification to the indigenous forest-dwelling birds of a series of New Zealand islands and to the passerines of the Cyclades Archipelago in the Aegean Sea. The analysis focuses on the reasons why the species-area relationship deviates from a perfect rank-correlation. For both avifaunas, most species are found remarkably predictably: they approximate a pattern in which each species occupies all those and only those islands larger than some species-specific minimum area. However, a minority of species in each avifauna do not conform to this pattern. Possible reasons for non-conformance include habitat differences among islands, anthropogenous extinctions, and equilibrium turnover. To the extent that the first two forces predominate, it would be far better to base conservation decisions on species lists from particular tracts that are potential refuges than on island occupancy patterns.
... 28 PACIFIC CONSERVATION BIOLOGY Four species (Rock Parrot, White-browed Scrubwren, White-fronted Chat, and Golden Whistler) have populations on the island which are isolated from those on the mainland, but no research has been conducted to establish if the birds differ from their adjacent mainland relatives. Analysis of vagrants to the island indicates that most of the species occurring on the adjacent mainland show a marked reluctance to cross open water and colonize the island or re-colonize in the event of the island's population being extirpated (Abbott 1980;Saunders and de Rebeira 1985b). Accordingly, special attention should be paid to these seven species, with monitoring programmes dedicated to them and attention paid to maintenance of their habitat and extending habitat where appropriate. ...
The avifauna of Rottnest Island, off the southwest coast of Western Australia, has been studied by three authorities from 1953-1963, 1980-1992 and 1998-2007. In addition, several annotated bird lists have been published since 1905. Over the period 1905 to 2007, 101 species have been recorded from the island, including 41 species of vagrant (species rarely seen with no pattern of occurrence) that have not changed in status over the 102 years. Of the 60 species recorded as part of the island's avifauna, 24 have apparently not changed in status over that period. Thirty-five species have changed in status and/or abundance, including nine species of transequatorial migrant; all Charadriiformes. Seven of these species were formerly absent or vagrants but now are regular visitors, several possibly as a result of range extensions. Two species of transequatorial migrant, formerly regarded as members of the island's avifauna, have become vagrants. Six passerine and one non-passerine species have resident populations that are isolated on the island with no populations on the adjacent mainland. Populations of three of these species are sufficiently different from mainland populations to constitute conservation management units. Rottnest Island is managed as a holiday resort. In the past this management has compromised some of the conservation values. Recommendations for dedicated monitoring programmes and management for the conservation of the island's avifauna are provided.
... Many studies have reported that species-rich assemblies contain specialized species and species-poor assemblies contain more generalist species (MacArthur 1955;Mac-Arthur et al. 1966;Lister 1976;Schoener 1977;Abbott 1980;Grant 1986;Kolasa and Li 2003;Carnicer et al. 2008;Weiner and Xiao 2012). Our results, at the metacommunity level, confirm this negative relationship between species richness and niche breadth. ...
Abstract Disentangling the mechanisms mediating the coexistence of habitat specialists and generalists has been a long-standing subject of investigation. However, the roles of species traits and environmental and spatial factors have not been assessed in a unifying theoretical framework. Theory suggests that specialist species are more competitive in natural communities. However, empirical work has shown that specialist species are declining worldwide due to habitat loss and fragmentation. We addressed the question of the coexistence of specialist and generalist species with a spatially explicit metacommunity model in continuous and heterogeneous environments. We characterized how species' dispersal abilities, the number of interacting species, environmental spatial autocorrelation, and disturbance impact community composition. Our results demonstrated that species' dispersal ability and the number of interacting species had a drastic influence on the composition of metacommunities. More specialized species coexisted when species had large dispersal abilities and when the number of interacting species was high. Disturbance selected against highly specialized species, whereas environmental spatial autocorrelation had a marginal impact. Interestingly, species richness and niche breadth were mainly positively correlated at the community scale but were negatively correlated at the metacommunity scale. Numerous diversely specialized species can thus coexist, but both species' intrinsic traits and environmental factors interact to shape the specialization signatures of communities at both the local and global scales.
... These nutritional challenges are expected to exert a strong influence on physiology mediating the interaction between the performance of the organism and the environment, with feedback to variation in reproductive success, survival and other life-history traits and demography (Ricklefs and Wikelski 2002). The link between nutritional physiology and life history through environmental constraints on food resources has, however, received scarce attention in island birds, despite the fact that it is often argued to be the mechanism behind resource-driven shifts of island population biology (Abbott 1980). Its study is therefore fundamental for explaining contemporary functional changes and their ontogenetic and population effects in island birds and, from a biogeographical point of view, to test for the drivers of the insular syndrome. ...
... The site-specific studies use theoretical principles in conservation biology that are often inadequately tested in the field. These principles are being used as a framework to guide management plans, with obvious limitations of being applicable in the spatial context (Abbott, 1980). Application of landscape ecological principles for prioritizing biodiversity-rich sites has the advantage of integrating spatial information, non-spatial information, and horizontal relationships in space and time. ...
The geospatial presentation of habitat status has become a key issue in conservation planning. The biodiversity character of the habitat provides the basis for prioritizing sites in the conservation effort. Since India is identified as one of the 17 megadiverse countries in the world, this task is of great significance. The Eastern Ghats are recognized as a diverse region with respect to flora and fauna. Landscape fragmentation and large-scale deforestation have been identified as the major reasons for the loss of biodiversity here. This paper uses landscape ecological principles for biodiversity characterization. Satellite remote sensing data has been used for the characterization of the landscape and stratification for ground inventory. A geographic information system has been used to spatially model the disturbance regimes and to integrate the ground-based non-spatial data with the spatial characters of the landscape. A spatial model incorporating ground-based biodiversity attributes of the landscape elements, land-use change patterns, disturbance regimes of the landscape, and terrain complexity have been used to delineate the spatial pattern of biological richness. The present approach is for prioritizing the biodiversity rich sites (with medicinal plants, ecologically and economically important species, RET species) has the advantage of integrating spatial and non-spatial information and horizontal relationships. The information is finally presented in space and time. This approach will facilitate conservation prioritization, systematic inventory, and continuous monitoring.
... These nutritional challenges are expected to exert a strong influence on physiology mediating the interaction between the performance of the organism and the environment, with feedback to variation in reproductive success, survival and other life-history traits and demography (Ricklefs and Wikelski 2002). The link between nutritional physiology and life history through environmental constraints on food resources has, however, received scarce attention in island birds, despite the fact that it is often argued to be the mechanism behind resource-driven shifts of island population biology (Abbott 1980). Its study is therefore fundamental for explaining contemporary functional changes and their ontogenetic and population effects in island birds and, from a biogeographical point of view, to test for the drivers of the insular syndrome. ...
Adaptation to insular environments often arises from changes and innovations in feeding behaviour allowing expanded foraging habits and an increased niche breadth. These shifts and innovations have traditionally been thought to be related to community-wide processes, but could also be the direct result of environmental constraints determining the abundance, availability and suitability of a particular food providing specific nutrients for survival, growth and reproduction. The link between environmental constraints on nutrients and life-history of insular organisms can help in understanding the convergent set of adaptations sustaining the ‘island syndrome’. We tested whether a potential insular nutrient shortage can drive diet shifts, nutritional biochemistry and growth stress, thus contributing to the modulation of life-history traits in a large passerine bird, the red-billed chough (Pyrrhocorax pyrrhocorax). Results supported the insular nutritional challenge hypothesis, linked to an insular insect shortage. An insect shortage may in turn have determined the reduced consumption of this source of protein but increased consumption of other arthropods, and notably fruits, by insular nestlings and fully-grown individuals. Island birds showed comparatively low circulating levels of nutrients and metabolites associated with the consumption of protein-rich animal matter as opposed to carbohydrate-rich vegetal matter, as well as high growth stress reflected in poor feather quality. We propose that feeding shifts derived from an insular insect shortage may exert a strong influence on the allocation of limited time, energy and nutrients among competing functions associated with physiological changes and investment in reproduction and self-maintenance. Traits and patterns generally defining the insular syndrome could thus be linked to particular insular nutrient constraints forcing feeding shifts and nutritional challenges with physiological, demographic and life-history consequences.
... The site speci®c studies use theoretical principles in conservation biology which are often inadequately tested in the ®eld. These principles are being used as a framework to guide management plans, with obvious limitations of being applicable in the spatial context ( Abbott, 1980). Application of landscape ecological principles for prioritizing the biodiversity rich sites has the advantage of integrating spatial information, non-spatial information and horizontal relationships in space and time. ...
Geospatial presentation of habitat status has become a key issue for planning conservation. Biodiversity characters of the habitat provide the basis of prioritizing sites in conservation efforts. Since India is identified as one of the 12-mega biodiversity countries in the world, this task is of great significance in the country. Biogeographers have long since recognized Northeast India as one of the most diverse regions with respect to flora and fauna. Since historic times, human interventions have influenced the land use and land cover in this region. Deforestation is mainly attributed to shifting cultivation and commercial logging of timber. This has resulted in fragmentation of the landscape, and landscape fragmentation and degradation have been identified as fundamental reasons for the biodiversity loss that has occurred. The paper uses landscape ecological principles for biodiversity characterization in the Meghalaya region of NE India. Satellite remote sensing data have been used for characterization of the landscape, and stratification for ground inventory. A geographic information system has been used to spatially model the disturbance regimes and to integrate the ground based nonspatial data with the spatial characters of the landscape. The vegetation types and land use have been mapped using Indian remote sensing (IRS) time series data. The various parameters (viz. patch shape, patch size, number of patches, porosity, fragmentation and juxtaposition) have been analysed on the most recent land cover map to spatially present the disturbance regimes. A spatial model incorporating ground based biodiversity attributes of the landscape elements, land use change patterns, disturbance regimes of the landscape and terrain complexity, have been used to delineate the spatial pattern of biological richness. This has been achieved using the landscape analysis package (LAP) developed at the Indian Institute of Remote Sensing. Habitat evaluation using ground based data and their spatial organization have been found to provide reliable information on the biodiversity distribution pattern. This approach for prioritizing the biodiversity rich sites has the advantage of integrating spatial and non-spatial information and horizontal relationships, so that the information is finally presented in space and time. This approach will facilitate conservation prioritization, systematic inventory and continuous monitoring.
... Despite having larger bills than its mainland counterparts in Spain (Cramp & Perrins 1994) and England (Newton 1966), the Azores Bullfinch consumes a higher proportion of small size foods: seeds less than 0.5 mm depth (Ramos 1995) and fern sori less than 4 mm length (Ramos 1996b). It also exploits a wider range of food types (fern fronds and moss tips; Ramos 1994b Ramos ,1995),and shows wider local movements (Ramos 1996a) than mainland Bullfinches (Newton 1964& 1967,Crocker 1987).A different distribution of habitats (Ramos 1996a) and feeding resources (Ramos 1995) seems to be important in explaining this niche expansion, a major ecological theme for island populations with fewer resources (Abbott 1980). Monthly weight variations of the Azores Bullfinch were slight, more closely resembling those of tropical birds (Ward 1969aWard , 1969b). ...
Information on biometrics, weights, breeding and moulting seasons is presented for several passerines, namely Chaffinch, Fringilla coelebs moreletti, Azores Bullfinch, Pyrrhula murina, Goldcrest, Regulus regulus azoricus and Blackcap, Sylvia atricapilla atlantis, captured from mid to high altitudes in S. Miguel island, Azores. The Chaffinch is the only species presenting sexual dimorphism in bill measurements, the Azores Bullfinch and the Goldcrest are sexually dimorphic in wing‐length, while the Blackcap showed no sexual dimorphism. All species bred between June and August and started moulting in August. Predominantly granivorous birds seemed to start breeding slightly later than predominantly insectivorous birds.
We studied the breeding biology of Tahiti Monarch Pomarea nigra , a ‘Critically Endangered’ forest bird endemic to Tahiti (French Polynesia). Nest activity was monitored from 1998 to 2002, and again from 2008 to 2015. During these 12 years, only 2–13 breeding pairs per year produced hatchlings. Egg-laying occurred all year, but usually increased between August and January, peaking around November. Of the 200 nests monitored, 33 (16%) were abandoned shortly after construction, 71 had an egg laid immediately after the nest were completed (34 %) and 96 nests (46 %) had a pre-incubation phase of 18.9 ± 1.9 days (3–62 days; n = 47 nests), during which the birds visited the nest on an irregular basis. Half (49 of 96) of these nests were abandoned before an egg was laid, with incubation subsequently commencing at the remaining nests ( n = 47). Although both sexes incubated for an average of 13.6 ± 0.3 days (range 13–15), the female usually spent more time incubating than the male. Only one young per nest was ever observed. The average nestling phase was 15.5 ± 0.7 days (range 13 to 20 days). Parents continue to feed the young after fledging for 74 ± 4.7 days (range 42–174). As with many tropical island endemics, the Tahiti Monarch has low reproductive productivity as indicated by the fact that: 1) only 56% of pairs attempt to lay an egg in any one year, 2) most pairs attempt only one brood per year and 3) the considerable length of the nesting and fledging phases. Because of its low productivity, maximising the reproductive success of the Tahiti Monarch is essential to secure its recovery.
In communities and biotic systems, diverse phenomena that may be interpreted as a compensation for species depletion of the biota are observed. The following kinds of compensatory mechanisms that limit the species diversity under extreme conditions are considered: raising the density of species populations; expansion of ecological niches; increase in the intraspecies diversity and multidominance, i.e. the predominance of one species within a wide spectrum of communities, assemblages, and guilds; increase in a relative (share of the total fauna or flora of a natural zone, region, etc.) species richness of taxocenoses, communities, particular floras and faunas; intense microevolutionary processes, intraspecies adaptive radiation, "explosive" species formation; canalized evolution (on the background of taxonomic depletion of the biota) leading to a high degree of morphological and ecological differentiation, i.e. increase in the amplitude of species differences within genetic groups. These phenomena are suggested to be a probable factors promoting the elevated rates of evolution in ancient ecosystems and at early developmental stages of phyletic groups.
Ten diurnal raptor communities (Falconiformes) were studied in continental and peninsular situations, and on landbridge and oceanic islands of various sizes, from Southern India to Southern Vietnam and from Sri Lanka to Java. An index of abundance was derived from 1-km(2) sample plots. A consistent decrease of species richness occurred from continent to peninsulas and to large landbridge islands, then more abruptly to oceanic islands. The impoverishment process was much faster for open habitat raptors than for forest species. and for rarest and most specialized raptors than for common and more generalist species. Large taxa survived on islands as well as smaller species. Specific habitat requirements, historical factors and forest fragmentation were probably more important determinants of community composition than land area itself. An insular syndrome was documented in forest species on islands, including significant examples of habitat niche expansion, interspecific segregation and density compensation. Some cases suggested that interspecific competition was involved. Such relaxation of habitat and density constraints may enhance the survival probability of these species on islands.
Marine ecological biodiversity research is a scientific field with few observational data to support a weak theory largely borrowed from terrestrial ecology and lacking in experimental verification. The relative lack of scientific interest and effort until recently was a consequence of the general feeling that marine biodiversity is far less threatened than terrestrial biodiversity. This view is not sustainable. There is now ample evidence of widespread changes in most coastal habitats in populated areas around the world (coral reefs, mangroves, seagrass fields, intertidal rocky shores and subtidal sediments on the continental shelf and margin) due to exploitation of marine resources, introduction of exotic species and the increased pressure from mariculture and fisheries. The sustainable exploitation of the seas requires development of a sound theoretical framework for marine biodiversity, including genetic, species and habitat diversity and especially the relationships between them. At the present state of knowledge such a general theory is still far from being reality. In this paper an overview is given of the main elements that an ecological theory of species diversity should include and what aspects of human pressure on the biodiversity of marine ecosystems should be given priority attention.
One familiar statement one hears about data analysis in ornithology is that traditional ornithologists accumulated facts, but did not make generalizations or formulate causal hypotheses (Emlen, 1981; Wiens, 1980). The approach of modern ornithologists, on the other hand, is said to be more theoretical. Modern ornithologists formulate hypotheses, make predictions, check the predictions with new data sets, perform experiments, and do statistical tests. Proponents of the modern approach frequently state their position in a condescending tone, and this is guaranteed to arouse the ire of those more committed to empirical research (Olson, 1981). In this essay, we hope to lessen the differences of opinion on this subject as they were recently expressed in the commentary section of The Auk (Austin et al., 1981). We agree with Popper (1959, 1972, 1983) that the goal of science is to develop better explanatory theories about processes in nature, but it does not follow that advances are made only by hypothesis testing.
One of the most important developments in modern ecology is the recognition that heterogeneity, or spatial pattern, is a key part of the structure and functioning of nature. No person working to understand the natural world or to manage natural resources can afford to neglect the fact that habitats, physical environments, resources, organisms, and other ecological objects have a complex spatial diversity (Bell et al. 1991 Caldwell and Pearcy 1994). However, ecologists and wildlife biologists have recognized spatial heterogeneity primarily at coarser scales. Coarse scale heterogeneity appears in such patterns as elevational gradients of plant and animal distribution, the contrast between different climatic zones with latitude, and contrasts between such community types as bogs and uplands, grassland, and forest (McIntosh 1991).
To do science means to construct theories and to adopt theoretical concepts in order to explain facts of nature (or man); if the world were what it looks like, science would be unnecessary. But how are the prevailing concepts in science in general, or in ecology in particular, vindicated?
The odonate fauna of five islands within the west coast of Peninsular Malaysia, namely Besar Island
(Melaka), Carey Island (Selangor), Pangkor Island (Perak), Penang Island (Penang) and Langkawi Island (Kedah)
were surveyed. A total of 54 species belonging to 12 family groups were identified. The highlights of the
collection is an endemic species of Pulau Langkawi and one new record for Peninsular Malaysia. Although
no other endemics were found in Besar Island, it was first record for the island.
This chapter is concerned with the change in communities caused by environmental fluctuations and the connection between observable change and change over longer periods of time in the past. Seasonal and annual fluctuations in environmental conditions over periods about decades are well known from direct observation and measurement. Fluctuations in climate, especially temperature, are probably the best known fluctuations for the longest period. In recent years, the records have been extended backward in time through analysis of tree rings, alluvial deposits, ice cores, and coral cores, and it has become apparent that temperature fluctuations display two patterns: periodic or quasi-periodic oscillations and state shifts. The chapter also suggests that the community has a core of species, and that other species are sometimes added or subtracted according to the environmental circumstances. Thus, the biological consequences of extreme climatic conditions experienced during the long-term study provide a view of community dynamics in the historical and prehistorical past.
Land birds breeding on 44 islands (size range 0.5-582ha) in the Vargskar archipelago of the Aland Islands (SW Finland) were censused. The islands were divided into 5 size classes and expected population sizes of land birds were estimated on the basis of habitat composition and population densities in equivalent habitats in Main Aland. Observed densities of most of the 56 species studied did not deviate from expected values; 11 species were more abundant on the islands than expected, including dominant generalists and species favoured by edges and bushy, heterogeneous habitat structure; 14 species had smaller populations on the islands than expected, but only 7 of them consistently so. The only species possibly showing density compensation is the dominant generalist Fringilla coelebs. Its populations on small islands are about doubled compared with expectation. Total densities are also higher than expected on small islands, but in most cases chaffinch contributes less than half to the increase. Autecological population responses rather than density compensation seem a plausible explanation of excessive population sizes of single species such as chaffinch. In these northern conditions island communities are assemblages of species colonizing the islands according to their autecological (especially habitat) requirements. -from Authors
Small, shallow seepage lakes in northern Wisconsin that have both low winter oxygen concentrations and low pH possess depauperate fish assemblages containing primarily or exclusively central mudminnows, Umbra limi, and yellow perch, perca flavescens. Six times during three years I determined the total densities of fish in five lakes by mark-recapture and catch-per-effort methods. The richness of the fish assemblages in these lakes varied from one to three species in a nested pattern. While seasonal variations in density occurred within and among lakes due to variations of growth, mortality, and recruitment, total densities overall were independent of species richness. the pattern, called complete density compensation, suggests that total densities are expressions of the lakes' similar abilities to support fish and that the species interact rather than being independent. An intense negative correlation between perch and mudminnow densities was found, suggesting a strong interspecific population dominance of perch over mudminnows. There was also indirect evidence that both competition (exploitation and interference) and predation by perch regulate mudminnow populations when the species co-occur. Because these assemblages were unpredictably variable in time and space, conclusions from single censuses would have been unreliable. An exercise simulating single seasonal censuses from each richness class showed that less than one-half of such single censuses would have produced the pattern of complete compensation that was observed in the field study. In general, my results support the idea that the relative importance of the factors that determine community structure, or even the factors themselves, can differ not only from assemblage to assemblage at any one time, but even from season to season or year to year within a single assemblage.
Cocos Island, Costa Rica, is a small and lushly forested island in the tropical eastern Pacific Ocean between Costa Rica and the Galapagos Archipelago. During two expeditions there, I quantified the stomach contents, available food (i.e., foliage-inhabiting arthropods sampled with sweep nets), foraging behavior, and morphology of the endemic Cocos Island Flycatcher (Nesotriccus ridgwayi, Tyrannidae). Nesotriccus individuals captured a diversity of arthropods in proportion to their availability (P » 0.1), using diverse foraging tactics. Stages of the birds' annual cycles differed during the two expeditions, but diet and foraging behavior were remarkably consistent. Fulgoroid Homoptera dominated stomach contents (43-64% of prey individuals), and probably explain why Nesotriccus foraged regularly with acrobatic pursuits (11-12% of all feeding tactics) much like a mainland Homoptera specialist, Terenotriccus erythrurus. Nesotriccus is morphologically and behaviorally distinct from its primarily frugivorous mainland relatives, Phaeomyias and Capsiempis; its wings and tail are structurally convergent with those of Terenotriccus, but its bill is comparatively longer and probably evolved for the capture of non-homopteran insects. Nesotriccus is a food specialist or generalist depending on one's frame of reference--available food, mainland insectivorous flycatchers, closest mainland relatives, or other resident land birds on the island. The diet and adaptations of Nesotriccus, in combination with other evidence, strongly support the hypothesis that insufficient abundance of many resource types precludes persistence in Cocos Island forests by virtually all but the endemic land birds. High endemism of the depauperate land bird fauna on the island appears to have resulted as much from this ecological impoverishment as from a lack of potential immigrants. /// La Isla del Coco es una isla costarricense pequeña y densamente arbolada en el océano Pacífico tropical, entre Costa Rica y el Archipiélago de las Galapagos. Durante dos expediciones a la isla cuantifique los contenidos estomacales, alimento disponible (es decir artrópodos habitantes de los follajes muestreados con redes a mano), comportamiento de forraje y morfologia del atrapamoscas endémico (Nesotriccus ridgwayi, Tyrannidae) de la Isla del Coco. Individuos de Nesotriccus utilizan diversas tacticas de forraje para capturar una diversidad de artrópodos en proporción a disponibilidad (P » 0.1). Las etapas del ciclo anual de las aves fueron diferentes durante las dos expediciones, pero la dieta y el comportamiento de forraje fueron consistentes de manera remarcable. Los contenidos estomacales estuvieron dominados por Homoptera (Fulgoroidae, 43-64% de los individuos presa) y probablemente eso explique porque Nesotriccus forrajea regularmente con cazas acrobáticas (11-12% de todas las tácticas de alimentación) de manera muy similar a la especialista en Homoptera del continente Terenotriccus erythrurus. Nesotriccus es morfológicamente y por su comportamiento, distinto de sus parientes del continente, primariamente frugívoros, Phaeomyias y Capsiempis; sus alas y cola son de estructura convergente con aquellas de Terenotriccus pero su pico es comparativamente mas largo y probablemente ha evolucionado para capturar insectos no-homopteros. Nesotriccus se alimenta como un especialista o no-especialista, dependiendo del marco de referenda en el que se lo ubique--comida disponible, los atrapamoscas insectívoros del continente, parientes más cercanos del continente u otras aves terrestres residentes en la isla. La dieta y adaptaciones de Nesotriccus, en combinación con otra evidencia, apoya fuertemente la hipótesis de que las aves, con exceptión de las terrestres endémicas, al no disponer de manera abundante de muchos tipos de recursos se les hace imposible la permanencia en bosques de la Isla del Coco. El alto endemismo de la paupérrima fauna de aves terrestres de la isla, parece haber resultado tanto por su empobrecimiento ecológico como por la falta de inmigrantes potenciales.
Huge numbers of Willow Warblers winter in East Africa, and at Lake Naivasha the Willow Warbler becomes the most abundant species in its guild; in some habitats half the individuals in the guild are Willow Warblers, and most likely such numbers influence the ecology and behaviour of the local species in the guild. In a four-month study restrictions/displacements in the presence, and releases in the absence, of Willow Warblers were observed in several of the local species. In the course of the autumn the Willow Warblers also changed their habitat distribution from groves to woodland, presumably because of interference from the numerous local birds in the grove-habitat. Shortly after arrival the habitat and microhabitat distributions (and foraging behaviour) of the Willow Warblers were almost identical to those of local species such as the Black-bellied Apalis. However, in the course of the autumn and winter clear divergences occurred between the two groups in several ecological and behavioural parameters.
Land birds were censused on 44 islands (size range 0.5-582 ha) in the archipelago of Aland, SW Finland. Species-abundance relations in the data of the 7 island type groups, defined on the basis of habitat composition, show statistically significant deviations from each other as assessed. Within each group the distributions were similar irrespective of sample size. A sampling metaphor for insular colonization is elaborated. The expected mean population size of each species is determined by 1) average regional abundance of the species, and 2) 'sampling efficiency' of any given island. Habitat composition is an important determinant of 'sampling efficiency'. Results emphasize the stochastic nature of colonization events and warn against making conclusions concerning turnover proneness of different species without data on population numbers - less abundant species are expected to turn over frequently. -from Author
(1) The breeding ecology of blue tits and coal tits shows very different patterns in Provence and in Corsica. For both species the onset of the breeding season is delayed by c. 3 weeks on the island and the clutch size is reduced by c. 30%. Furthermore Corsican tits never have second broods whereas 26% of blue tits and 60% of coal tits do have second broods on the mainland. (2) Breeding success is 6.4 young raised per pair for the blue tit and 9.5 for the coal tit on the mainland, as compared with 2.6 and 3.0 respectively in Corsica. The proportion of breeding adults older than 1 year is only slightly higher on the island. (3) These results which illustrate a lower population turnover on the island are discussed in the light of current theories dealing with the evolutionary significance of clutch size and associated life history parameters. (4) Insular characteristics of the food supply and its variability on a year round basis are shown to be important factors responsible for these differences in population ecology. (5) Comparisons of the growth rates of nestlings and of feeding frequencies between the mainland population and the Corsican population do not support the hypothesis that low reproductive rates on the island could be attributed to intraspecific competition. Nor do these results support the view that breeding ecology is determined through mechanisms of optimization of reproductive effort in a trade-off between clutch size and associated life history parameters. Rather they fit Ashmole's hypothesis on the significance of clutch size. (6) It is concluded that a low amount and only a small surplus of food supply during the breeding season are sufficient to explain why the breeding ecology of Corsican tits is so different from that of the continental ones.
Interspecific competition has influenced the distribution and morphology of Darwin's finches, but data do not support the hypothesis of competitive exclusion in 2 particular cases; the exclusion of G. fortis from Genovesa and G. magnirostris from Espanola by G. conirostris. The absence of fortis and magnirostris from the 2 islands cannot be explained by the lack of suitable foods or by the failure of the species to reach these islands. Geospiza fortis may be absent because of a combined (diffuse) competitive effect of magnirostris, conirostris and difficilis. A breeding population of magnirostris may be lacking on Espanola because whenever magnirostris arrive, in small numbers, they die, depart or hybridize with conirostris. -from Authors
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 rarefaction, 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 individuals, and several other abundant mainland species were scarce on the islands as well. Two species (Cychrus caraboides and sterostichus 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 autecological characteristics of the species, such as dispersal ability and habitat preferences.
Marsh Harriers Circus aeruginosus in New Zealand have undergone both niche expansion and niche shifts. Niche expansion has occurred in the range of habitats hunted over and nested in, because Marsh Harriers in New Zealand ex- ploit all of the range of habitats used by Australian Marsh Harriers as well as hunting over short grass and frequently nesting in tall vegetation well away from wetlands. Harriers in New Zealand have shifted from exploiting the traditional Marsh Harrier food of waterfowl to consuming more of the abundant Sheep Ovis aries carrion and road-killed animals. These niche changes and increases in the density of the island population have been facilitated by ecological release from diffuse interspecific competition and differences in resource availability. The interspecific ecological changes observed in New Zealand are vrobablv the result of behavioural and ecological flexibility within the species rather than recent genetic change.
Two hundred and forty-three species of birds have been recorded from the Torres Strait. Of these 87 are resident and breed on the islands, 26 remain for the wet or dry season only, 73 cross the Strait on a regular or irregular basis and 57 are vagrant visitors or await confirmation. The number of land bird species found on islands is more a function of the area of forest or woodland than of the total area of the island. Both oceanic and land bridge islands are present in the Torres Strait. Some species found on land bridge islands appear to have been stranded there when sea levels rose. The ranges of some birds found only on land bridge islands are mutually exclusive of several wide ranging species found on most other islands., Evidence is presented that competition has determined the nature of the avifauna on some Torres Strait islands. The Torres Strait apparently represents a barrier to the movements of 28% of the species, including 38% of the land birds, that are shared by Australia and New Guinea. Many populations of Australian birds cannot, therefore, be replenished from New Guinea. Nearly half the birds seen in the Torres Strait are migratory. The most numerous Palaearctic passage migrants are the Mongolian Plover and the Grey-tailed Tattler. Many passage migrants breed in Australia and over-winter in New Guinea. Half of these cross the Strait at low altitudes and several appear to need the Torres Strait islands as resting places, especially when travelling south into the prevailing adverse trade winds. Seven migrants breed on Torres Strait islands. Human effects on the avifauna are localised although introduced species, the House Sparrow and the Common Mynah, have become resident on three islands within the last four years. Apart from these introductions, the avifauna of only Murray Island changed naturally during the study period between 1977 and 1982.
Theory suggests that the persistence of metapopulations will be influenced by the degree of synchrony in the dynamics of their component populations. Various studies have shown that climate can promote synchrony in the size of adjacent populations linked by dispersal, but fewer studies have examined the effects of climate on underlying demographic rates. We studied annual variation in the timing of breeding and reproductive rates in Song Sparrow (Melospiza melodia) on islands linked by dispersal to determine whether biotic factors acting at local scales or climatic factors acting at a regional scale were more influential of variation in demography. The onset of egg laying varied markedly among years but was roughly synchronous across islands within years. Despite this synchrony, island populations varied markedly in reproductive rate, mainly from spatial variation in nest depredation and brood parasitism. In general, populations farther from Vancouver Island and with fewer resident predators experienced less nest depredation and brood parasitism, and higher reproductive rates, than populations closer to Vancouver Island. Our results show that even when climate acts regionally to synchronize reproductive timing in adjacent populations, its effects on reproductive rate may be overridden by biotic factors that vary among populations.
Depredación de Nidos, Parasitismo de Cría y Variación Reproductiva en Poblaciones Isleñas de Melospiza melodia
Habitat expansion is a commonly recognized feature of the insular syndrome. It has been explained either by restricted dispersal, intraspecific spillover resulting from density inflation, benign and predictable climate, or by the ecological release that results from species impoverishment. The latter hypothesis has been frequently invoked to explain shifts and/or broadenings of elevational ranges on islands. In this paper, we compared the elevational distribution of 85 terrestrial breeding bird species on a Mediterranean island (Corsica) with their mainland counterparts in a control area of similar altitude, latitude, and climate (Eastern Pyrenees). We calculated specific altitudinal amplitudes in both areas from the upper and lower limits of the bird ranges in the breeding season. We then calculated Island/Mainland Amplitude Ratio (IMAR) for each species. The ratios we found showed an overall trend in favor of range compressions on Corsica, despite a lower number of species on the island than on the mainland. However the well-differentiated subspecies-level endemics are the ones more likely to expand their ranges on the island. Their frequency is highest in the middle of the elevational gradient, in the cool forests situated between 1400 m and 2000 m. The non-Mediterranean and non-alpine nature of endemism on Corsica, together with the niche broadening of the endemic forms, can be explained by taking into account Pleistocene glacial-interglacial cycles. The resulting up and down and back again shift of the bioclimatic belts tended, in turn, to eliminate the lower ranging and the higher ranging species from the elevational gradient. The belt that persisted throughout the cycles was the mid-altitude belt, where differentiation processes had sufficient time to lead to endemism. This mechanism also tended to broaden the species ranges, both by selecting among the colonizers those that already had wide ranges on the mainland and by exerting selective pressures on the residents in favor of the broadening of their ranges. More recently, human activities on the island have favored the immigration of undifferentiated species whose elevational ranges are still relatively low.
Information on plant-food resources is crucial for assisting the conservation of the Azores bullfinch Pyrrhula murina. This bird is confined to part of the native cloud forest in eastern S. Miguel (Azores), which is currently facing considerable changes.The diet is described and the time of food scarcity identified. Floristic variation in areas with and without birds is examined. The diet presents marked seasonal variations, from invertebrates and herbaceous and fleshy-fruit seeds in summer and autumn to fern sporangia, tree seeds, fern fronds and flower buds in winter and spring. The bird needs a mosaic of vegetation types, and seems heavily dependent on flower buds of Ilex perado at a time of food scarcity. Areas without birds have significantly lower densities of the food plants that are consumed during this period. Large-scale invasions of exotic species are threatening some of the forest mosaics. The implications for understanding the distribution and abundance of the Azores bullfinch are discussed and conservation measures proposed.
The effects of patch size on the abundance of sessile invertebrates were investigated for 2 kinds of patchiness in a subtidal habitat in southern Australia: discrete pieces of substratum that were surrounded by water (isolated patches), and areas that were cleared within a background of other sessile organisms (nonisolated patches). The species composition of nonisolated patches following reoccupation was independent of patch size. Vegetative growth of organisms adjacent to the patches was the major means of reoccupation. Most larvae that recruited into the patches were overgrown, so that the species composition of the patches reflected the outcomes of interference competition among residents of patches. As a result, sponges and colonial tunicates were the most common taxa, with bryozoans and serpulid polychaetes being excluded. Occupation of isolated patches was strongly size-dependent. On small substrata, species' abundances reflected their ability to colonize substrata by planktonic larvae, with a small number of patches containing tunicates, which have the potential to monopolize such patches. Larger substrata had a higher probability of being colonized by tunicates and sponges, in addition to bryozoans. Species compositions and abundances in these large patches were influenced most strongly by interference competition, rather than by recruitment.-from Author
Populations of the lesser white-toothed shrew, Crocidura suaveolens (Pallas, 1811), from Corsica show an increase in adult body size associated with a decrease in litter size. The average number of embryos in wild Corsican females is smaller (mean 2.6, n = 62) than in mainland females (mean 4.6, n = 173). A breeding experiment was run for 4 years, yielding three generations. Under standard breeding conditions, the differences between island and mainland populations were maintained and were significant (median litter size was 2 for Corsica and 5 for the mainland). These differences in life-history traits were therefore proved experimentally to be genetically determined. Hypotheses concerning the mechanisms responsible for these differences are discussed.
Live weight, morphological measurements, and moult of about 400 birds of 16 species of native Fijian passerines are described. Morphological changes associated with sex, age, and geographical distribution are reported. Heavier and presumably more terrestrial subspecies (Lamprolia v. victoriae, Pachycephala pectoralis torquata, and Myiagra a. azureocapilla) are found on Taveuni. Three species — Pachycephala pectoralis, Petroica multicolor, and Zosterops lateralis — are compared with the same species found in Australia and New Zealand. Birds moult in all months, but mainly between September and April. Wing moult was commonest in December. Ten of 13 species show seasonal moult. Circumstantial evidence indicates that about 25% of the species moult body feathers while breeding.
Patterns of taxonomic differentiation and geographical distribution of West Indian birds suggest that taxa may pass through phases of increasing and decreasing geographical range. Such sequences are referred to as taxon cycles. Although decline may often lead to extinction, new phases of expansion, accompanied by increased or shifted habitat distribution are also possible. The taxon cycle is a historical hypothesis, but its existence was formerly inferred from contemporary, indirect evidence. Molecular studies of land birds in the West Indies now provide relative ages for taxa based on genetic differentiation among island populations. These age estimates confirm that older populations tend to have restricted geographical and ecological distributions. That ecology and geography are strongly correlated with age across taxa also suggests that the time course for evolutionary change through the taxon cycle is relatively consistent among independently evolving populations. Because young taxa have continuous distributions within the West Indies, gaps in the ranges of older taxa indicate extinctions of island populations. Starting from this premise, one may estimate exponential extinction rates of about 50% per million years for island populations in the Lesser Antilles, which indicates an average population life span of two million years. The relative timing of expansion phases suggests that cyclic dynamics of populations are not driven by extrinsic factors such as climate and associated habitat change during glacial cycles. Alternatively, such cycles may be intrinsic, perhaps driven by lags in the evolutionary responses of host and parasite populations. This is suggested by observed variation in the prevalence of blood parasites among island populations of the same species. The taxon cycle concept provides a useful paradigm for understanding variation among species in geographical range, ecological distribution, and vulnerability to extinction.
The resident avifauna of a coastal scrub community on St. Kitts, West Indies, was surveyed in 1982 in order to examine what factors may be influencing its composition. Fifteen species were observed, three of which (Dendroica petechia, Tiaris bicolor and Columbina passerina) accounted for over 61% of the total observations. The results are briefly discussed in light of some current theories on avian community structure.
A 1960-71 study of populations of color-banded ant-following antbirds of three species on a tropical-forested lowland reserve, Barro Colorado Island, showed that the small species (Spotted Antbird, Hylophylax naevioides) remained stable at about 20 pairs/km^2. A medium-sized species, the Bicolored Antbird (Gymnopithys bicolor), decreased from about 3 pairs to 1.5 pairs/km^2. A large species, the Ocellated Antbird (Phaenostictus mcleannani), declined from 1.5 pairs/km^2 to near extinction--only one female remained in early 1971. Two of three other species that regularly follow army ants showed relatively stable populations, but a third large species (Barred Woodcreeper, Dendrocolaptes certhia) declined from two pairs to local extinction. Prior to 1960 a very large ground-cuckoo that follows ants had already become extinct there. Thus, the three largest of the seven original species that regularly followed ants were gone or nearly gone by 1970. The decrease in numbers of regular ant-following birds was not made up by increases in occasional followers. Detailed studies of antbirds showed no clear reasons for declines, except that annual mortalities of adults were high in Ocellated Antbirds (about 30%) compared to Spotted Antbirds (15%-17%) and nest losses perhaps higher in the former (96% compared to 91%). Nest mortalities were slightly lower (88%) and adult mortalities intermediate (about 25%) in Bicolored Antbirds. Female Ocellated Antbirds had higher mortalities than males. The antbirds renest repeatedly during long nesting seasons, up to 14 times per year for Ocellated Antbirds. However, to replace females of this species under Barro Colorado conditions 19 nestings per year would be needed. Concurrent listing of all birds of the island showed that 45 species of breeding birds, 22% of the avifauna present when the island was made a reserve, had disappeared by 1970. No new species replaced them. Of the lost species 13 are forest birds, in danger if forests are cut elsewhere. The other species, second-growth and forest-edge birds, have been crowded out by growth of the forest. Loss of species from this tropical reserve, especially the part apparently caused by the small size and isolation of the reserve, poses problems for conservation and ecological studies of tropical biotas. It is suggested that large future reserves have corridor zones to each other, that is, that intensive human use not preempt too much area nor interrupt immigration of animals or plants from one refuge to another.
This paper analyzes factors determining the extent of density compensation on islands: i.e., is the summed population density of individuals of all species on islands equal to the summed mainland density as a result of niche expansions and higher abundances of island species compensating for the absence of many mainland species? In addition, a method is described for estimating bird population densities based on analysis of the time dependence or mist-netting yields. Puercos Island in the Pearl Archipelago off Panama has less than one-third as many resident birds species as comparable mainland habitats. Analysis of the Pearl avifauna suggests that about one-quarter of the island species may be relicts of the Pleistocene land bridge and that the remainder are subsequent over-water colonists. The successful colonists are a highly nonrandom sample of the mainland avifauna in such respects as family composition, social structure, and second-growth habitat origin. Song-based censuses and analysis of mist-netting show that Puercos has a slightly density of individuals than the mainland. Niche shifts between islands and mainland, or among different islands, include habitat expansions, wider ranges of vertical foraging strata, abundance increases checkerboard distribution patterns, and decreased morphological variability. Comparison of the present study with other studies shows that summed population densities on islands may be higher than, comparable to, or less than mainland levels, depending upon the particular island, habitat, and group of animals studied. Among factors affecting the extent of density colonists less appropriate to the vacated habitat, tending to lower island densities; and underrepresentation of large species on islands, tending to increase island population densities for a given biomass.
Seton rock shelter (35⚬ 59'S, 137⚬ 03'E) is located in the southwest of Kangaroo Island, South Australia. Excavation of the late Pleistocene deposit in the rock shelter has provided a rich assemblage of mammal, bird and reptile remains dating from more than 16 000 BP to about 10 000 BP. Analysis of these remains shows that the late Pleistocene fauna of Kangaroo Island was more extensive than the depauperate island fauna of today. The disappearance of many species reflects a reduction in open vegetation probably due to a combination of climatic change, the separation of the island postglacially by rising sea level, and the disappearance of a human population within the last 5000 years. The deposit also provides evidence for the contemporaneity of man and one of the extinct Pleistocene kangaroos, Sthenurus cf. gilli, at 16 000 BP.
A recurrent theme in science is that the utilitarian harvest from new theoretical developments comes after some delay and often in unanticipated quarters. So it can be said of modern island biogeography whose founders, MacArthur and Wilson (1963), perceived the simplicity and analytical tractability of isolated ecosystems. Now it is becoming increasingly apparent that the methods and the way of thinking they developed are extensible to a much larger range of situations, including the design of faunal preserves.
It is commonplace for islands to have fewer bird species than adjoining mainlands. In this respect Tasmania is no different to other islands. Lack (1969) has pointed out that until recently this was attributed to difficulties of dispersal, a view which he rejected. The two most recent studies of the Tasmanian avifauna (Ridpath & Moreau, 1966; Kikkawa & Pearse, 1969) both attributed the low number of species breeding in Tasmania to the barrier effect of Bass Strait. In this chapter it is argued that the barrier effect alone is inadequate and that additional factors must be taken into account if the impoverishment of the Tasmanian avifauna is to be explained adequately. The comprehensive theory of island biogeography proposed by Macarthur
&
Wilson (1963, 1967) is believed to provide this explanation.
Niche breadth varies with competitive pressure. When most of the pressure experienced by a species is from a single close competitor, its niche tends to be broader in the absence than in the presence of the competitor. When ‘diffuse competition’ (the combined effects of numerous more distant competitors) is more significant, the niche tends to be broader on islands with few than with many species. We summarize all known examples of such niche shifts for New Hebridean birds, based on comparing conspecific populations on different New Hebridean islands or New Hebridean populations with those in another archipelago. The commonest niche shifts are spatial ones affecting type of habitat, altitude or vertical foraging range. Other shifts affect size and number of islands inhabited: shifts from small to large islands and shifts in ‘incidence’. The remaining types of shifts are in diet and in abundance. We conclude that competition is the proximate cause of distributional limits for most New Hebridean species. We hypothesize that rapid behavioural responses of colonists to altered competition mainly affect spatial parameters of niches. Subsequent slower genetic changes modify foraging technique and diet and may produce shifts into forest and montane forest according to so-called taxon cycles. Further work is needed to test directly this proposed sequence of behavioural and genetic changes in colonists and to compare the importance of interspecific aggression and depletion of resources as proximate mechanisms of competitive exclusion.
A genus of Australian birds (Melithreptus, Meliphagidae) shows no significant geographic variation over extensive continental ranges but marked morphological shifts with isolation. The changes are investigated with respect to shifts in basic ecology of the species and relative to the associated avifauna in each case. The following findings were reached: 1) Commonly a larger, and a smaller, species of Melithreptus occur together, differing in mean linear measurements by 10%. In isolated Tasmania the differences are greatly exaggerated. In southwestern Australia (isolated forest segment) and on Kangaroo Island, from which the larger species is absent, a smaller species (different one in each case) has a longer bill and tarsus. 2) The smaller species are either foliage gleaners (M. lunatus, M. affinis), or else feed in the branches (M. brevirostris). The larger species (M. gularis, M. validirostris) are much less specialized in their choice of feeding zones. 3) Evolutionary shifts can only, in part, be explained by ecological shifts and interrelationships within Melithreptus. Significantly, they occur under conditions of marked impoverishment in the associated avifauna, e.g., Tasmania, Kangaroo Island, and southwestern Australia have only half the number of passerine species as the mainland of southeastern Australia. These faunas, particularly Tasmania, prove to be lacking, or deficient in, certain basic types of birds. Thus creepers (Climacteris) and nuthatches (Neositta) are absent. 4) Detailed feeding zone studies show that, in Tasmania especially, various species of birds have moved into the resultant vacant niches. Pre-eminent among these are Melithreptus validirostris, that has now become in part a trunk-prober and in part a bark-prizer, and has acquired corresponding morphological attributes. M. affinis, a foliage-gleaner, becomes more warbler-like in its shorter bill and hallux. Apart from M. validirostris three other species of birds have become part trunk-feeders in Tasmania and show morphological changes adapting them for this. These are another honeyeater, a thrush, and a warbler. The present study shows how impoverished insular faunas come to reach a state of ecological balance by a redivision of ecological niches and ways of life among the component species. This is achieved not by species abandoning their former way of life when they enter a new niche but by their becoming increasingly diversified, i.e., they occupy a wider spectrum. The changes in bill, tarsus, and hallux length that characterize insular populations of birds in different parts of the world are interpreted relative to this.
Foliage arthropod collections from Puerto Rico second growth vegetation are analyzed at five sites from sweep samples taken in the dry season (February 1972). Data on taxonomic composition, diversity, evenness, and trophic structure are presented for these sites and compared with published data for other tropical and temperate areas. We conclude that the second growth vegetation of Puerto Rico supports an arthropod community of comparable diversity to that of other Caribbean islands or a Kansas woodland. This diversity is far lower than that of continental Central America. Surprisingly, the proportion of predators in our island samples is high, sometimes approaching half of the individuals. A significant correlation was found between the number of adult insects and number of spiders, both for the Central American mainland and for the Puerto Rican samples. However, the ratio of spiders per insect is far higher for the island collections.
I studied the foraging of Yellow Warbler (Dendroica petechia) and American Redstarts (Setophaga ruticilla) on several small islands of varying vegetational composition off the coast of Maine. Both species used deciduous growth more than predicted by chance alone. Yellow Warblers foraged slightly lower than Redstarts; Redstarts used dead limbs and hawked for insects more often than Yellow Warblers. On islands with mixed forests both species fledged young regularly; there they set up largely exclusive territories. Partitioning appeared to be in response to certain vegetational characteristics; little evidence was obtained that direct interactions were of major importance in this regard. Most male Redstarts in the latter areas were adults; most males on small spruce-clad islands had first-year plumage. Only one species occupied any small spruce-clad island, and seldom did it fledge young. Usually a male did not attract a female in such cases. No clear correlation occurred between the size of the standing insect crop, the tendency of these species to occupy an island, and their ability to fledge young. While Parula (Parula americana), Myrtle (Dendroica coronata), and Black-throated Green (D. virens) warblers displayed a highly developed vertical division of space and a well-defined interspecific social hierarchy (Morse 1971), Yellow Warblers and Redstarts divided space horizontally and did not demonstrate a well-defined interspecific social hierarchy. Correspondingly, one may find up to three species of spruce-woods warblers on an island too small to support more than one pair of a given species, but never both Yellow Warblers and Redstarts in such a situation.
1. In North America and México there is a strong tendency for island birds to have a longer tarsus and bill than their mainland counterparts; but there is no such tendency for them to have a longer wing and tail. 2. Although climate and body-size are known to influence the size of tarsus and bill the larger dimensions on islands are considered to be adaptations primarily to ecological conditions. The bill is longer because it deals with a greater range of food-sizes, and the tarsus is longer because a greater variety of perches is used. 3. The differences in usage have arisen as a result of the absence, on the islands, of species with similar ecological requirements, which has permitted some of those present to extend their activities and occupy at least part of the vacant niches, sometimes in new habitats. 4. It is suggested that the same ecological conditions and responses have influenced the evolution of large body-size of island rodents in particular, and of mainland animals of several phyla in general.
This paper presents the results of an analysis of bill length differences among sympatric congeneric species associations of 46 bird families inhabiting tropical, subtropical, and temperate areas. The bill ratios of large to small species within these associations, called ratios of character difference are usually large (greater than 1.14) 1) among the members of certain families which appear to feed on food of relatively low abundance; 2) in sympatric congeneric species associations on islands, especially small islands; and 3) among birds whose body sizes are relatively large in proportion to the total abundance of their food. Large ratios are assumed to reflect significant differences in dimensional or physical properties of the food or its immediate environment. Models considering the distribution of food biomass with respect to size are used to argue that where the diversity of potentially competing species is low, due to low food abundance relative to the size of the feeding birds or for other reasons, food partitioning by size or dimensional property of the immediate food environment as a means of avoiding competition is feasible. In contrast, where a large number of potentially competing species occurs, as is likely to be the case for birds which consume relatively abundant food, rather than evolve the precise perceptual mechanisms necessary for discriminating small food size spans if food partitioning by size is to be utilized, species will consistently avoid competition by evolving differences in feeding habitat or foraging behavior. It is suggested that the most probable first step in the evolution of sympatric congeneric associations on islands and in some mainland situations is the partitioning of food by size, physical properties, or dimensional properties of its immediate environment, rather than by habitat. The first species to invade an area is likely to expand its habitat considerably, but still feed on a rather restricted range in dimensional or physical properties of the available food or its immediate environment, due to limitations of structure and efficiency on the individual bird, resulting in the most favorable opportunities for colonization by closely related species leading to coexistence to be for the invading species which utilize different ranges of these properties. The utilization of different food size ranges in many and overlapping habitats as opposed to taking similarly-sized food in different, more restricted habitats, being the more complete utilization of the available food supply for a small number of species, also favors the initial evolutionary step resulting in large ratios of character difference. Many insectivorous families, but only a small proportion of others, all of whose small-billed associations have small ratios of character difference, possess other associations in which the largest or larger species are separated from the other members by a relatively large character difference, and have still other associations, entirely composed of large-billed birds, with high ratios among all members. Two possible explanations are larger consuming biomasses for the larger species of an association and a food abundance distribution curve which decreases with increasing food size. The transition zone, defined as the range of bill length over which small ratios change to larger ones (greater than 1.14), begins at smaller bill lengths in insectivorous families than it does for more omnivorous groups. Insectivorous families in general show more large ratios in tropical areas than in temperate zones, related to the much greater number of large-billed tropical insectivorous birds. This preponderance can be explained by a lower consuming biomass of populations of tropical species and/or a less sharply declining food abundance distribution curve with increasing food size for insectivorous families in the tropics. Some implications of this study for the concepts of niche overlap and behavioral stereotypy are discussed.
(1) This paper deals with the underlying mechanisms of the hunting behaviour and selection of prey species by great tits feeding their young at the nest, and is based on observations made mainly in mixed broad-leaved woodland in Wytham near Oxford, England, and partly in larch plantations in Yamanaka, Japan, using both automatic cameras (41 000 photographs taken) at ten nests for 150 nestling-days and direct observations at six nests for 63 nestling-days. (2) A brief description of general tendencies in nestlings' diet as observed by various authors in different parts of the world is given first, as an introduction to this study. The major prey species in the breeding season are invariably Lepidoptera, particularly the larvae. (3) Apart from spiders taken during the first few days after hatching, the composition of prey species in the diet of nestlings has no particular relation to their age. It is suggested that spiders are of particular importance, from a nutritional point of view, at a certain stage of the chicks' growth. The nestlings were regularly fed with grit and snail shell, whose function seems to be related solely to mechanical grinding of food in the gizzard. (4) The seasonal succession of the prey species in the nestlings' diet throughout the breeding season is described, and the collection sites for many of the prey species are discussed. (5) Factors governing the utilization of prey species by tits to feed their young are highly complicated and are discussed first in terms of observed facts. On the whole, there seems to be no direct correlation between the biomass of the prey in the habitat and the tits' selection. The occurrence, in the nestlings' diet, of many lepidopterous species coincided with their time of pupation, which suggests that the behaviour of the prey has some importance in relation to their exposure to predation by tits. The effects of taste and conspicuousness of the prey species and of alternative prey occupying different micro-habitats are discussed in relation to the hunting efficiency of tits. (6) The factors governing the utilization of prey by tits are discussed further with the aid of a theoretical model. Tinbergen's theory of search images is critically reviewed, and an alternative theory proposed. The model is based on one fundamental assumption: that the predator tries constantly to maximize its hunting efficiency within its limited ability to perceive the abundance of food in various parts of the hunting area. (7) The concept of `profitability', defined as the amount of food the predator can collect for a given amount of hunting effort, is introduced into the model, and the relationship between the profitability and the density of a given prey species is investigated. From this model, some conclusions are drawn, and tentatively tested against the available observations. As the profitability of a prey species is determined not only by the density but also by the size of the prey and the method of hunting of the predator, and as the predator tries to get the most out of the whole complex of prey populations in the habitat, a direct correlation between the numbers of a given prey taken by the tits and its density cannot be expected. Instead, it is shown that the tendency expected from this model fits, without apparent contradictions, both Tinbergen's observations and my own. (8) It is also shown that the size of prey has some bearing on the selection of food by tits and influences differences in the composition between the diets of adults, fledglings and nestlings. (9) Some suggestions are made in concluding remarks as to the aspects of the problem which need to be considered in future studies.
Communities of breeding, non-raptorial land birds were studied in nine major habitat types (secondary grassland and scrub, young and old secondary forest, mature lowland forest, cloud forest, mangroves, savanna, residential land) in each of five Caribbean areas (Panama, Trinidad, Jamaica, St. Lucia, St. Kitts). In each habitat, the frequency of occurrence of individual species was determined in ten 20-min observation periods. Foliage height profiles were determined for all areas except St. Kitts. Data on frequency of occurrence were converted to indices of absolute abundance. Ecological release, involving both increase in the average number of habitats occupied per species and increase in within-habitat abundance, was extensive, and complete density compensation or overcompensation occurred in Jamaica, St. Lucia, and St. Kitts. Dropout of species along the species diversity gradient from Panama to St. Kitts appeared to be random with respect to generic or familial status. Habitat distribution appeared to shift from being strongly influenced by interspecific relations in Panama to being largely independent of such influence in St. Kitts. /// Исследовали комплексы гнездуйщихся нехищных наземных птиц в 9 основных типах местообитаний (вторичные луга и кусгарниковые заросли, молодой и сгарый вторичные леса, зрелый пойменный лес, горный лес, мангровые заросли, саванна, поселки) на каждой из пяти территорий на побережье Карибского моря (Панама, тринидад, Санта Лючия, Св. Киттс.). В каждом местообитании определяли встречаемость отдельных видов в течение 10 20-минутных наблюдений. Для всех территорий, кроме Св.Киттса, определяли профили высоты листвы. По данным встречаемости рассчитывали показатели абсолютного обилия. Экологическое высвобогдение, включающее как среднее число местообитаний, занятых одним видом, так и увеличение плотности внутри каждопо местообитания, было экстенсивным, и полная компенсация или сверхкомпенсация численности наблюдалась на Ямайке, Санта Лючия и Св.Киттс. Вьшадение видов по градиенту видового разнообраия от Панамы до Св. Киттса по-видимому случайно по отношению к их принадлежности к родам и семействам. Характер распреления по местообитаниям колеблется от строгой зависимости от межвидовых отношений - в Панаме до полной независимости от них - на Св.Киттсе.
Variation in tarsus length was studied in 20 species of birds which occur on the Tres Marias islands and adjacent mainland of Mexico. Seventy-eight intraspecific comparisons were made of the variation exhibited in the two regions. In nine instances differences were statistically significant; in five of them the mainland sample was the more variable, in the remaining four instances the island sample was the more variable. Thus no clear trend exists towards greater or smaller variation in this dimension on the Tres Marias islands. Furthermore there is no evidence of morphological change in the island populations in the last hundred years. The differences in variation between island and mainland populations are not transitory, manifested only as the island populations are approaching new adaptive modes, but are the stable result of selection acting on either tarsus or total leg length differently in the two environments. Differences in intraspecific variation in tarsus length can be accounted for by an hypothesis put forward by Van Valen (1965) and which is restated as follows. Under spatially uniform environmental conditions, selection favours little inter-individual variation in feeding ecology and associated morphology by acting strongly against individuals departing widely from the average phenotype and under spatially varied (patchy) conditions, the opposite occurs. A prediction is made that differences in morphological variation, and associated differences in feeding ecology, exist between the sexes of some species. The morphological aspect of the prediction is shown to be correct, but data on the ecological aspect are lacking. What is not known is why the differences in variation between regions and between sexes occur in the observed directions, and why these species show differences in variation and others do not. Any general theory of morphological variation in birds should provide answers to these questions.
This study analyzes the circumstances under which certain lizards shift and fail to shift their habitats. At each of 20 localities, I measured the structural habitats utilized by all the diurnal arboreal lizard species as well as the availability of those habitats. I selected localities so as to include for four widespread species (Anolis grahami, A. sagrei, A. carolinensis, A. distichus) nearly all of the species-combinations in which they occur. Data were fitted to equations that (1) adjust for locality-specific differences in vegetation, and (2) estimate the direction and intensity of apparent interaction between sympatric forms. Shift was valuated both for species and separately for age and sex classes within species. Female-sized individuals shift more frequently than do adult @M @M. Linear equations that evaluate sympatric forms one at a time showed the strongest apparent competitors for a widespread from to be (1) adult @M @M rather than female-sized individuals, especially when adult @M @M represent the widespread species; (2) species of similar climatic habitat; (3) classes of similar size (especially against female-sized individuals of widespread species; and (4) classes of large size (especially against adult @M @M). The most abundant classes are the strongest apparent competitors for A. distichus but not for the other widespread species. These results are unchanged or strengthened when different habitat categories or nonlinear equations are used. Combining all sympatric forms into locality-specific linear equations supports Results 1 and 2 but is inconclusive for Results 3 and 4. The parameter proportional to the size of a refugium from interference is estimated for some cases to be significantly greater for female-size individuals than for adult @M @M. In general, results imply that animals similar to widespread forms in some niche dimension other than structural habitat are those most likely to cause shift in structural habitat. In addition, they suggest existence of a competition function with respect to size: in such a function intensity of competition is uniquely determined by the direction and amount of size difference, regardless of the competitors' absolute sizes. Competition intensity appears to (1) decrease overall with increasing difference in size, (2) be greater for a given size difference if the competitor is larger than if it is smaller, and (3) decrease at nonconstant rates, such that near complete size similarity there is a more rapid decline in intensity for smaller than larger competitors. Morphological differences between populations and short-term field observations suggest that both evolutionary and behavioral mechanisms regulate habitat shift.
We present an analysis of bird distribution in small islands in the northern Lesser Antilles colonized principally from Guadeloupe. In spite of great differences among the islands in soils, rainfall, and vegetation, their avifaunas are strikingly uniform. We found that species inhabiting coastal scrub on the source island performed better as colonists than inhabitants of interior rainforest, suggesting that humid forests in the target islands would hold drastically impoverished bird communities. This proved not to be the case. Diversities in the small-island rainforest communities were compensated by the substitution of coastal scrub species for missing forest counterparts and the expansion of vertical foraging zones. In progressing from species-poor to species-rich communities in equivalent habitat, the number of trophic guilds remains constant, while the number of species per guild and the tightness of species packing increase. We conclude that the faunal uniformity of islands colonized from Guadeloupe results from nonuniform dispersal abilities coupled with ordering ecological constraints: versatility in habitat occupancy, trophic status and size in relation to guild neighbors.
The densities of breeding birds on 39 small islands and in two mainland study plots were compared. The combined densities were similar on the mainland and on larger islands despite much reduced species number on the islands. On smaller islands combined densities were higher. Densities were positively correlated to shore length in three species foraging mainly along the shores and negatively to the number of other species in the willow warbler Phylloscopus trochilus and the chaffinch Fringilla coelebs. All these five species occurred in much higher densities on the islands compared to the mainland. In some guilds density compensation was found on the islands, where fewer species occurred. /// Сравнивали плотность гнездующихся птиц на 39 небольших островах и в 2-х участках материка. Уровни общей плотности сходны на материке и более крупных островах, несмотря на то, что видовой состав на островах сильно обеднен. На небольщих островах общая плотность птиц выше. Плотность находится в прямой зависимости от длины береговой линии у 3-х видов, питающихся преимущественно в прибрежной зоне, и в обратной зависимости - у некоторых других видов - Phylloscopus trochilus и Fringilla coelebs. Все эти 5 видов встречаются в гораздо большем количестве на островах в сравнении с материком. В некоторых сообществах отмечена компенсация плотности на островах, где видовой состав обеднен.
Four types of islands, which form a primary succession sere, have characteristic coastal bird communities (Anseriformes and Charadriiformes) on the Krunnit Islands (North Gulf of Bothnia, 65 degrees 25 prime N, 25 degrees 00 prime E). Recovery of the communities started after the island group was protected in 1936. Bird populations have been censused in twenty breeding seasons between 1939 and 1972. (1) The main changes observed were the increase of gull populations and related changes in the distribution of duck populations. Protection conferred a great advantage for the large gulls, but the effect was negligible on the wader populations. (2) Species diversity on the four island types differed consistently throughout the study period. Diversity increased with the successional stage of an island. (3) Protection caused a decrease of species diversity, because the re-established gull and tern populations now dominate in the communities. Thus, high species diversity does not always indicate a high conservation value of a bird community. (4) Recovery of the communities altered the relationship between island area and the number of species on small islands. (5) Rates of species turnover in the island group were of the order of 0.01 species per year. Calculations indicated that these northern islands are very rapidly--in less than 10 years--saturated with coastal bird species.
(1) This paper interprets the distributional ecology of breeding land and fresh-water birds of the New Hebrides, in the light of immigration-extinction equilibria. (2) The species-area relation has a lower slope (z=0.05) for the New Hebrides than for archipelagoes nearer the colonization sources of New Guinea and Australia. This difference is attributed to higher intra-archipelagal immigration rates in the New Hebrides, because superior overwater colonizing species are increasingly overrepresented among colonist individuals at increasing distances from the sources. (3) Isolated New Hebridean islands have fewer species than similar-sized central ones. The decrease in species number with distance is steeper on smaller islands. (4) Assignment of species to so-called incidence categories shows that most species are widely distributed geographically as well as ecologically within the archipelago. These categories are correlated with species' habitat preference and level of endemism. Few species have passed beyond the stage of recent colonists in a taxon cycle. (5) A model of incidence functions based on immigration-extinction equilibria for a single species may explain the otherwise puzzling restriction of some species to the larger islands. (6) Many species show untidy distributional gaps along the island chain, while other cases of tidy linear distributions cannot reasonably be attributed to arrested invasions. These patterns suggest that present-day distributions are simply one snapshot of a kaleidoscopic sequence of distributions, generated by immigrations and extinctions. Changes in the intra-archipelagal distributions of a few species on even medium-sized and large islands can be detected on a time scale of decades.
Microtus pennsylvanicus and M. ochrogaster are sympatric in southern Indiana grasslands. From June 1965 to August 1967 four populations were lived trapped, three of them in 0.8-hectare (2-acre) outdoor pens. Both species increased during 1965 and reached peak densities in summer 1966. Microtus ochrogaster declined abruptly that fall and remained low; M. pennsylvanicus declined the following spring. One of the fenced populations increased to a density about three times that of its unfenced control. By early fall 1966 it had nearly destroyed its food resources and then suffered a severe decline associated with obvious overgrazing and starvation. No such overgrazing has been seen on any unfenced grasslands in this area. Dispersal is probably necessary for normal population regulation in these voles, since fenced populations seem unable to regulate their density below the limit set by starvation. Both species bred extensively in the winter of 1965-66 during the phase of population increase. There was little or no breeding during the winter after the peak. Survival of females in the trappable population of both species was high and relatively constant until the end of the cycle. In males, periods of low survival punctuated the increase and peak phases, and these periods of low male survival did not occur at the same time in the two Microtus species. Some mortality processes are thus highly specific for sex and species. In the fenced populations survival rates were very high and no sporadic male losses occurred. Increasing and peak populations of M. pennsylvanicus and M. ochrogaster are characterized by adults of large body size. During the increase and peak phases some voles stopped growing at low weights (30-40 g) while others reached high asymptotic weights (45-55 g). The demography of these Microtus species in southern Indiana is similar to that of other cycle voles and lemmings in temperate and arctic areas.
In this paper I attempt to answer the question, "What (if any) differences occur in the foraging of isolated wood warblers (Parulidae) and ones in large multispecies populations?" Parula (Parula americana), Myrtle (Dendroica coronata), and Black-throated Green (D. virens) Warblers were studied on seven small spruce-clad islands off the coast of Maine, each island supporting one pair of one to three of these species. Data obtained were compared with earlier studies of these species in large adjacent populations. Though seasonally isolated, all individuals belonged to the large gene pools of the appropriate species on the adjoining mainland. While the insular forests resemble those of the mainland, they are in general shorter and more open. When only one species was present, it was always the Parula Warbler; when two species were present, they were always the Parula and Myrtle. Black-throated Green Warblers only occurred in the presence of the latter two species. diversity increased as the size of forest and proportion of foliage in tree crowns grew. Parula and Myrtle Warblers experienced greater nesting success than Black-throated Green Warblers. Black-throated Green Warblers foraged much as they did in large populations; however, Myrtle and Parula Warblers demonstrated considerably more plasticity in foraging. When Black-throated Green Warblers were absent, the two other species tended to modify their foraging. On the one island studied in detail where only Parula Warblers occurred, they appeared to expand their foraging range farther than where Myrtle Warblers were present. Overlap in foraging usually decreased as species compositions became more depauperate. Though variability occurred among individuals of each species, variability of an individual in two different years appeared as great. Black-throated Green Warblers dominate the other two species socially, and the implications of this situation upon distributions in larger populations and on small islands are discussed. I hypothesize that the stereotypy of the Black-throated Green Warbler represents an adaptation to the extremely high density it experiences in large populations, which make up the major part of the gene pool. The higher degree of plasticity seen in Parula and Myrtle Warblers may be appropriate to their subordinate roles.
Bird population densities on the island of Cañas, Pearl Archipelago, Panama, were estimated by regression analysis of mist net captures of resident birds. The Cañas mist net capture rate is very similar to those from adjacent Puercos, which is one seventh as big but otherwise similar. This not only confirms the main results of the Puercos study but also seems to rule out the action on these birds of the boundary phenomena described for mice by Krebs et al. in which confined populations greatly increased in density because of the small enclosure. The results are consistent with observations made by Diamond on southwest Pacific birds.
Adaptive evolution in island birds is investigated with special reference to the birds of Tasmania, a continental island 26.000 square miles in area that lies 140 miles off southern Australia. The avifauna is a typical insular one being numerically impoverished (only 43 species of passerine birds compared with 89 in equivalent habitats on the adjacent mainland), and lacking certain "basic kinds" of birds (e.g., true trunk feeders are absent) The study emphasizes shifts in vertical feeding zones and in morphological attributes associated with perching and feeding (e.g., bill, tarsus, hallux). The findings are as follows: 1. A series of island species have moved into the vacant trunk feeding and underexploited arboreal, foliage-gleaning, adaptive zones; 2. these are species that, on the adjacent Australian mainland, already feed to some slight extent in these zones; 3. the shifts invariably involve a broadening of, or increased diversity in, feeding; 4. there is a broad redivision of ecological roles and adaptive niches on the island; vacant niches are eliminated, and a new state of integration and balance is achieved within the avifauna.
Distribution, abundance, diet, and beak morphology of the six Geospiza finch species were studied at eight sites on seven Galapagos islands. The resulting information was used to test the theories of Lack and Bowman that interspecific competition (Lack) and floristic and food differences among islands (Bowman) determine the ecological and morphological characteristics of the finches. Both factors were found to be important in different aspects of finch ecology. Most of the 21 populations studied spent more time foraging for seeds and fruits than for insects. Most populations had generalized diets and nine out of 18 pairs of sympatric populations had diets overlapping by 50% or more. Diet breadth was positively correlated with variety of available foods (classified by an index comprising measures of size and hardness), but was not correlated with abundance or biomass of sympatric populations of finches (potential competitors). Competitive release, in the form of large population biomass on islands with few congeners, was not found. Nor was population biomass related to variety of available food. Overlap in diet between two species was greatest when the species were most similar in abundance and body size. Interspecific competition is indicated by the distribution and morphology of the finches. The absence of four combinations of species cannot be attributed to change: (1) G. conirostris and G. fortis, (2) G. conirostris and G. scandens, (3) G. difficilis and G. fuliginosa, and (4) G. scandens and G. difficilis. These absences cannot be attributed to the absence of suitable foods. and sites with similar floras and suites of food types do not necessarily have similar ground finch faunas. The ecological and morphological similarity of members of each of the four pairs suggests an inability to coexist for competitive reasons. In contrast, where only two species occur together on an island they tend to differ markedly in size (beak and body) and diet. Species with large beaks can eat larger and harder seeds and fruits than species with small beaks, and as a consequence they tend to have more diverse diets. Species with large beaks also eat medium-sized seeds and fruits quicker than species with small beaks. Species with small beaks may be able to deal with small soft seeds more efficiently than species with large beaks, but the data are not clear on this point. In addition, small species with small beaks have a metabolic advantage over large species with large beaks. Variety of available foods influences the large species more than the small species: the two largest species, G. magnirostris and G. conirostris, occur only on sites where plants producing large and hard seeds and fruits are plentiful. Food variety apparently does not influence the degree of diet overlap. The number of plant species on an island statistically determines the number of land-bird species in general, and Geospiza species in particular, which occur on that island. The influence is probably mediated through food supply, since 53% of the variation in Geospiza species diversity among the eight sites was accounted for in a multiple linear regression analysis by diversity of available seeds and fruits. We conclude that food supply and interspecific competition have jointly determined the ecological course of the radiation of Darwin's finches and the resulting pattern of species diversity. Interisland variation in vegetation favored the initial steps of differentiation. Competitive interactions among species influenced later stages by determining which ecological types could coexist on an island with a given array of foods.
A comparative study of chaparral and pine forest bird communities on Santa Cruz Island and adjacent mainland areas was made during 1969—72. Five fewer species occurred in the island chaparral bird community and four fewer species in the island pine forest bird communities. Changes in bird species composition occurred most notably in the island pine forest, which is utilized by species commonly found in the chaparral. No significant changes in niche breadths were observed for the communities in general; however, a slight tendency for increased foraging height diversities on the island was observed. Average niche overlap values between species present on both the mainland and the island are greater on the island, mainly because of an increased vertical habitat overlap. By use of the observed mainland densities and competition coefficients composed of mainland overlap values, island densities were predicted for four bird species that show greater densities in the island chaparral community. Hence, competitiv...
With the study of the equilibrium theory of island biogeography pioneered by MacArthur and Wilson (1963, 1967), increasing attention has been paid to the study of turnover rates (Mayr 1965; Diamond 1969, 1971; Power 1972; Terborgh and Faaberg 1973). The failure of bird species turnover rates to show the predicted negative correlation with island size in the California Channel Islands (Dia-mond 1969) raises questions as to what factors other than island size may be involved in determining species turnover. Previous studies of avifaunal turnover have treated faunas as a whole and have not differentiated turnover rates for rare species from those of common species. Since very large birds and species at high levels on the food chain often exist at relatively low densities, these organisms would be expected to have a greater probabil-ity of extinction on small islands than those species which maintain larger populations (Brown 1971). A theoretical basis for this hypothesis can be derived from Gilpin (1974). He has shown (pers. comm.) that extinction rates should be a negative exponential func-tion of K, and thus should be very sensitive to small population size. In this paper we present heretofore un-published data and a review of the literature on the avifauna of Santa Barbara Island (Channel Islands, Santa Barbara County, Cali-fornia). These data provide the bases for a comparison of the turnover rates of various groups of breeding birds, e.g., "birds of prey" and "songbirds." This comparison supports the hypothesis relating turnover rates to trophic levels. Santa Barbara Island is a volcanic island approximately 38 miles (61 km) from the nearest mainland and 24 miles (39 km) from the nearest large island, Santa Catalina Island. It is about 1.75 miles (3.8 km) long and 1.1 mile (IS km) wide and has a maximum ele-vation of 635 ft (193 m). Its surface area is approximately one square mile (2.6 km2). Corey (1954) and Valentine and Lipps (1967) presented different theories as to the geologi-cal history of the island and Philbrick (1972) provided an up-to-date account of the island' s vegetation. METHODS The authors made observations on 29 January, 24 March, and between 15 May and 23 July 1972. Other observations cited include those of E. Lowell Sumner, Jr., who visited the island in April 1939, and those of Tared Diamond who was on the island from 23 to 25July 1968. Dr. Diamond also provided records of other visitors in 1967 and 1968. In order to obtain percent turnover, a baseline of species' presence or -absence is needed. In light of the small size of Santa Barbara Island and the fact that there were early records for the two most cryptic species of small land birds listed as breeding, we feel that the work of Howell (1917), Willett (1933), and Maillard (1918) taken together provide an accurate baseline for determining extinctions and invasions of birds (see table 1). For the same rea-sons, we also have confidence in the data of Sumner and Diamond, whose censuses were designed specifi-tally to assess the species breeding on the-island: Although Lvnch and lohnson (1974) feel that data on gonadal conditions are important ' for proving nesting, for our own avifaunal records we felt that it was inappropriate to collect individuals from very small island populations in danger of extinction. Furthermore, we feel that behavioral criteria such as territorial defense or persistent use of burrows are preferable to gonadal data, since the gonads of migrants may show enlargement equivalent to that expected from resident breeding birds (Lofts and Murton 1973).
The number and identities of species coexist-ing at a particular locality are not fixed for-ever, but result from dynamic interplay be-tween local extinctions and immigrations. While this dynamic structure must apply to any local community, it is particularly con-venient to study on islands, because of their sharp boundaries. In their well-known theory of island biogeography MacArthur and Wil-son (1963, 1967) proposed that the number of species on an island approaches an equilibrium between extinctions and immigrations, and that populations are subject to turnover. It is likely that large differences in turnover rates will be found if one compares the same taxo-nomic groups on islands of different area, iso-lation, latitude, and habitat, or if one compares different species on the same island. The measurement and understanding of these dif-ferences is beginning to emerge as a major empirical and theoretical problem, as a problem in assessing the importance of group selection and understand-ing the evolution of social behavior (Levins 1975, Wilson 1975:1X-116), and as a major practical problem in conservation strat-egy (Terborgh 1974a, 197413, Diamond 1975, 1976, Wilson and Willis 1975, Sullivan and Shaffer 1975). A convenient situation for studying these problems is provided by the land and fresh-water breeding birds of the Channel Islands off the coast of southern California. The eight islands of this group vary in area (A) from 2.6 to 249 km2, in distance from the mainland (d) from 20 to 98 km, and in number of land and non-swimming water bird species breed-ing in a given year (S,,,,) from 7 to 39 (see Philbrick 1967, Power 1972, Johnson 1972, and Jones 1975 for maps and table of areas and dis-tances). As of 1917, when A. B. Howell' s monograph Avifauna of the Islands off the Coast of Southern California was published, 170 species of birds had been recorded from the Channel Islands. By 1976 this number had increased to 325. All but five of these 155 additions were of non-breeding visitors, re-corded principally by us and by other observ-ers since 1968. The reason is that most of the early ornithologists who visited these islands were collectors and oologists mainly interested in obtaining specimens or egg sets of the breeding birds, some of which are considered endemic or nearly endemic subspecies. Conse-quently, the breeding avifauna of all the Chan-nel Islands was more thoroughly documented by 1917 than was the non-breeding avifauna (see appendix p. 545 for discussion). In 1968 one of us (J. D.) visited each of the Channel Islands l-3 times, plus the nearby Mexican island group Los Coronados, to sur-vey the breeding avifaunas for comparison with the surveys summarized by Howell (1917). On each island he found that there had been turnover, reflected both in dis-appearances of some former breeding popula-tions and in breeding presence of some for-merly absent or non-breeding species. A brief account of the results, and of estimated turn-over rates in relation to A, d, and Serl, was pub-lished (Diamond 1969). One of Diamond' s findings was that some breeding populations had immigrated and become extinct several times on the same island between the early 1909' s and 1968. Thus, surveys separated by many decades must have underestimated turn-over rates and might only have revealed the tip of the iceberg of community dynamics (see Diamond and May in press for examples). For organisms as mobile as birds, and islands as close to the mainland as the Channel Is-lands, it is likely that there will always be a long waiting list of potential immigrants; many more unsuccessful attempts at colonization than attempts that succeed even briefly; and many more brief successes and rapid failures than foundings of a colonist population that survives a long time. Hence repeated surveys at one-year intervals were clearly required to reveal the dynamic structure of the avifauna more accurately. Such studies of turnover at one-year intervals have the further advantage of reducing interpretative problems associated with habitat changes and effects of man which develop over longer intervals.
Kangaroo Island has 54 per cent of the species of landbirds that breed on Fleurieu Peninsula, 14 km distant, and about 80 per cent of the species on Yorke or Eyre Peninsulas. Though often visited by ornithologists during the last 67 years, 55 species of landbirds known on the mainland hare never been recorded, 33 others have been recorded less than five times. The marked avifaunal impoverishment of the island is probably not because of differences in habitat or vegetation, but because these 88 species have immigrated very seldom to the island.The pattern of distribution of 226 species of landbirds over southern Australia, including Tasmania and the islands in Bass Strait, suggests that nearly 25 per cent of these arrived postglacially in coastal South Australia. Probably only 25 of the 90 species absent from Kangaroo bland were there in the past but have became extinct. Sixteen of these occur in Tasmania but not on any Bass Strait island and are presumably extinct there also. One native species has established itself on Kangaroo Island in the last 67 years.The theoretical expectation that island populations should have more variable bills or tarsi than mainland populations was confirmed respectively for male Acanthiza pusilla and female Phylidonyris pyrrhoptera.
Regulation is defined as the return of a population to equilibrium density. An operational definition of regulation is convergence to a single density by subpopulations which have been manipulated previously to different densities. The equilibrium density may be fixed or variable. If the equilibrium is variable then regulation may produce instability (numerical inconstancy) and non-density-dependence. Population inertia is the tendency for a population to resist changes away from its current density. If speed of regulation is defined as |s|, the speed of convergence to equilibrium, then inertia is 1/|s|. The evolution of mechanisms of inertia involves changes in the demographic functions, mediated through physiology or behavior, which keep the rate of numerical change low. It is not clear if populations are control systems or non-control systems, which makes the convergence experiment difficult to interpret theorectically. Experiments and observations are needed which will try to distinguish, among stable populations, between those with tight regulation and those with high inertia.