A. O. Nicholls

Habitat fragmentation and its lasting impact on Earth's ecosystems

Urgent need for conservation and restoration measures to improve landscape connectivity. We conducted an analysis of global forest cover to reveal that 70% of remaining forest is within 1 km of the forest’s edge, subject to the degrading effects of fragmentation. A synthesis of fragmentation experiments spanning multiple biomes and scales, five continents, and 35 years demonstrates that habitat fragmentation reduces biodiversity by 13 to 75% and impairs key ecosystem functions by decreasing biomass and altering nutrient cycles. Effects are greatest in the smallest and most isolated fragments, and they magnify with the passage of time. These findings indicate an urgent need for conservation and restoration measures to improve landscape connectivity, which will reduce extinction rates and help maintain ecosystem services.

Diversity of Eucalyptus species predicted by a multi-variable environmental gradient

SummaryChanges in species diversity are examined in relation to a multidimensional environmental gradient using Eucalyptus species in south-eastern Australia. By fitting a generalized linear model, the response of the community parameter, species diversity, is shown to be related to three environmental variables, mean annual rainfall, mean annual temperature and a relative measure of solar radiation. The effects of rainfall and temperature were both statistically significant and large, solar radiation was significant but small. However, the influence of the two major variables was not independent but interacted in a complex way that prevents adequate description of species diversity as a function of either variable alone. Possible biological explanations of the complexity are discussed in terms of limiting conditions at low temperatures, and competition between guilds of species at high temperatures and medium to high rainfall.

Colonisation of native tree and shrub plantings by woodland birds in an agricultural landscape

Tree planting has become a cornerstone strategy for natural resource management in agricultural landscapes, yet its contribution as habitat for woodland birds has not been fully investigated. A case study from the Holbrook region in southern New South Wales was used to assess woodland birds in young plantings of native trees and shrubs. Ground-foraging insectivorous woodland birds were under-represented in the plantings, partly due to a lack of native forb diversity (wildflowers) and leaf litter. Of 69 woodland bird species recorded over a three-year period, 48 species (70%) occurred in planted sites, 59 species (86%) occurred in remnant woodland, and 34 species (49%) occurred in adjacent paddock sites. The greater diversity of birds in planted sites relative to paddock sites was mostly due to understorey birds. The proportion of mist-netted birds recaptured was similar in both planted (15%) and remnant woodland (16%) sites, suggesting that individual birds were staying in planted sites. The proportion of woodland birds showing breeding activity (as measured by the presence of a brood patch) was slightly lower in planted sites (24% of all woodland species) than in remnant woodland (29%). Birds such as the superb fairy-wren, red-browed finch and southern whiteface were more likely to occur in planted sites, suggesting that plantings provide unique, transitional-stage habitat within agricultural landscapes. Restoring native forbs, as part of a broader strategy of woodland management, will help to reverse the decline of ground-foraging insectivorous woodland birds in agricultural landscapes.

Do tour boats affect fur seals at Montague Island, New South Wales?

) and tour boats at Montague Island were investigated between November 1997 and November 1998. The fur seals were in four haul-out sites, which are referred to here as colonies. The study was instigated by the manage-ment requirement of the National Parks and Wildlife Service of New South Wales to determine effects of disturbance from tour boats on the fur seal colonies. At each of 84 inspections, distance between the boat and the colony was measured and seal behavior (or response) was recorded 11 times at 15-second intervals as the boat moved toward the seals. This period of 2.5 minutes was approximately the time tour boats stayed at a colony. Behavior of the fur seals ashore was recorded in four catego-ries of increasing disturbance from “Resting” to “Many moving.” From analyses using multinomial models, the probability of observing a given response by the fur seals and the pattern of the responses as a function of distance from the colony were both infl uenced by the colony under observation. In general, fur seals’ responses were signifi cantly correlated with distance between the study boat and the colony, and with the size of the colony (i.e., number of fur seals visible ashore). In all cases, the probability of the colony remaining in the “Resting” category decreased as the distance between the colony and the study boat decreased. Similarly the probability of the colony showing the maximum response (“Many moving”) increased as the distance decreased. The probability of New Zealand fur seals “Resting” was higher than for Australian fur seals. Tour boats approaching the colonies had a relatively small effect on the fur seals; few or none of them ran to the sea. Based on results from this study, we recommended that the minimum approach distance of tour boats to the fur seal colonies at Montague Island should be 40 m; other recommendations involved how tour boats approach the fur seal colonies. The former has been gazetted as a government regulation and the other recommendations have been incorporated into the license conditions for the tour boats operators.Key words: Fur seals; Tour boats; Wildlife tourism; Wildlife interactions

Fragmentation affects plant community composition over time

&NA; Habitat fragmentation can lead to major changes in community composition, but little is known about the dynamics of these changes, or how community trajectories are affected by the initial state of habitat maturity. We use four landscape‐scale experiments from different biogeographic regions to understand how plant community composition responds to fragmentation over decades. Within each experiment, we consider first whether plant communities in the most‐fragmented treatments diverge in composition from plant communities in the least‐fragmented treatments. Second, because communities embedded in different fragments may become more similar to one another over time (biotic homogenization), we asked whether beta diversity – compositional variation across space – declines among fragments over time. Third, we assessed whether fragmentation alters the degree to which temporal change in fragmented landscapes is due to ordered species losses and gains (nestedness) versus species replacements (turnover). For each of these three questions, we contrasted patterns of compositional change in mature communities following fragmentation (disassembly; n = 2 experiments) with patterns in newly‐developing plant communities in fragments cleared of vegetation (assembly; n = 2 experiments). In the two studies where communities were disassembling, community composition in the most‐fragmented habitats diverged from that in least‐fragmented habitats. Beta diversity within a fragmentation treatment did not change over time at any of the four sites. In all four experiments, temporal patterns of compositional change were due mostly to species turnover, although nestedness played a role in the least‐fragmented sites in two of the studies. Overall, the impacts on community composition varied among landscape experiments, and divergence may have been affected by the maturity of the plant community. Future comparisons across ecosystems that account for species identities (vs simply richness) will be critical for predicting the effects of fragmentation, managing mature plant communities in remnants, and restoring plant communities where habitat has been lost.

Female-biased dispersal in a spatially restricted endemic island bird

Dispersal of individuals before their first breeding attempt or between subsequent attempts facilitates spatial and temporal gene flow within and among populations. However, in species on oceanic islands, dispersal is often restricted to a single island, and thus, the risk of inbreeding is particularly high in those small, closed, and isolated populations. One of the mechanisms that may prevent inbreeding within island populations is sex-biased dispersal, which results in close kin of the opposite sex not being in the same area for breeding. In this study, we investigated dispersal patterns, and their costs and benefits, in the Chatham Island black robin, a small passerine confined to two small islands. We found that black robins practice a resource defense mating system as male black robins were more likely to divorce than change territory between breeding seasons. Natal dispersal was female-biased in both the proportion of birds dispersing and the distance dispersed. Bird density in the natal year increased the proportion of birds dispersing in both sexes. Breeding success was reduced for females after natal dispersal. Breeding dispersal was rare and female-biased in proportion only. Regardless of sex, black robins were more likely to disperse after losing a mate, but females dispersed further than males. This study suggests that in closed populations of island species with limited habitat, sex-biased density-dependent dispersal may be a mechanism that minimizes inbreeding.Significance statementDispersal of individuals facilitates gene flow within and among populations. However, in species on oceanic islands, dispersal is often restricted to movement within a single island. Few studies have investigated dispersal and its costs and benefits in spatially restricted species. Here, we studied the endangered Chatham Island black robin, a songbird confined to two small islands. We found that on an island, where habitat is extremely limited, males are highly territorial and they are more likely to change partners than territories. Bird density in the natal year forces both young males and females to move, but females are more likely to disperse and move further than males. Sex-biased density-dependent dispersal may be a mechanism that minimizes inbreeding. This is particularly important for threatened island endemic species where maintaining high genetic diversity ensures the population’s long-term viability.

Breeding failure and nestling body mass as a function of age of breeding females in the endangered Carnaby's Cockatoo, Calyptorhynchus latirostris

The ecology of a population of the endangered Carnabys Cockatoo, Calyptorhynchus latirostris, was studied from 1969 to 2015, with breeding data collected for 28 of those years. Data were available on the known breeding failure rates of females of known age (banded as nestlings in the study area) and females of unknown age (banded as adults), and on the condition of their nestlings, as assessed by the nestlings’ body mass and age. Females in their first two breeding years had failure rates four times that of older and more experienced females. Younger females (4 to 6 years old) were more likely to nest up to three weeks later than older females (7 to 27 years old), and the oldest females in the study area were more likely to nest three weeks later than those at least 10 to 19 years old. There was a trend for oldest females to produce lighter nestlings than young females. Despite the length of the study, few data are available on longevity in the species, other than one known age female breeding in her 27t...

Fur seals and sea lions (family Otariidae) on the breakwaters at Adelaide’s Outer Harbor, South Australia

Long-nosed fur seals (Arctocephalus forsteri) and Australian sea lions (Neophoca cinerea) on the breakwaters at the mouth of the Port River estuary at Adelaide’s Outer Harbor were counted from 2004 to 2015. Observed counts were modelled using a generalised linear model. Fur seal numbers have been increasing since 2011; for sea lions there was a small discernible annual trend in counts. Counts of fur seals varied seasonally; most annual maxima were in August or September with modelled peak numbers around 9–11 September. The maximum count of fur seals was 79 in September 2015. For sea lions, the model predicts annual peaks in the period 28 August to 19 September. The maximum count of sea lions was nine in September 2009. The haulout sites on the Outer Harbor breakwaters are easily accessible by boats, including pleasure craft. In particular, the seaward end of the outer breakwater is a popular spot with recreational anglers whose lines are often within a few metres of the seals. We propose that a management plan should be developed involving a study of the effect of boat approaches on seals utilising the Outer Harbor area followed by education coupled with enforcement.

Trajectories of floristic change in grassland: Landscape, land use legacy and seasonal conditions overshadow restoration actions

Questions How does ground-layer plant composition respond to the imposition of woodland habitat restoration treatments following the removal of long-term pastoral management? Do different vegetation types have different trajectories of change? Location A long-term ecological research site comprising temperate eucalypt grassy woodland and forest in south-eastern Australia converted from pastoral use to conservation management. This has involved the implementation of habitat restoration treatments in addition to the cessation of livestock grazing and fertilizer inputs. Methods We surveyed ground layer floristic composition over a 4-year interval, in 96 1-ha sites that had been subjected to combinations of restoration treatments aimed at improving the condition of the woodland habitat for fauna: 1) Reduced kangaroo grazing intensity; 2) Addition of coarse woody debris; and 3) Burning. We used nonmetric multidimensional scaling to plot the sites, and to analyse the average trajectories of floristic change for each of six initially identified vegetation types, and the restoration treatments. We partitioned Bray and Curtis dissimilarity measures to rank individual species’ contributions to floristic change in each vegetation type between 2007 and 2011. Results The identities of the six vegetation types identified at time zero was strongly retained over the four-year observation period. There was generally a uniform change across the vegetation types that was the result of increases in biomass of the characteristic dominant perennial grasses, and increases in some native forbs. The two vegetation types with evidence of past fertilization showed some convergence with native vegetation types due to the decrease in some exotic species. The restoration treatments had no significant influence on species composition. Conclusions The native herbaceous vegetation in the woodland was largely resistant to compositional change, although seasonal conditions increased the biomass of the perennial grasses defining the different vegetation types. However, sites with an evident history of past fertilization and notable amounts of exotic pasture species changed slightly but significantly, with some pasture species declining and floristic convergence with native vegetation over four years. These rates of change need to be considered in the application of vegetation offsetting policy. This article is protected by copyright. All rights reserved.