A multi-scale analysis of western spruce budworm outbreak dynamics

Context

Forest insect outbreaks are influenced by ecological processes operating at multiple spatial scales, including host-insect interactions within stands and across landscapes that are modified by regional-scale variations in climate. These drivers of outbreak dynamics are not well understood for the western spruce budworm, a defoliator that is native to forests of western North America.

Objectives

Our aim was to assess how processes across multiple spatial scales drive western spruce budworm outbreak dynamics. Our objective was to assess the relative importance and influence of a set of factors covering the stand, landscape, and regional scales for explaining spatiotemporal outbreak patterns in British Columbia, Canada.

Methods

We used generalized linear mixed effect models within a multi-model interference framework to relate annual budworm infestation mapped from Landsat time series (1996–2012) to sets of stand-, landscape-, and regional-scale factors derived from forest inventory data, GIS analyses, and climate models.

Results

Outbreak patterns were explained well by our model (R ² = 93%). The most important predictors of infestation probability were the proximity to infestations in the previous year, landscape-scale host abundance, and dry autumn conditions. While stand characteristics were overall less important predictors, we did find infestations were more likely amongst pure Douglas-fir stands with low site indices and high crown closure.

Conclusions

Our findings add to growing empirical evidence that insect outbreak dynamics are driven by multi-scaled processes. Forest management planning to mitigate the impacts of budworm outbreaks should thus consider landscape- and regional-scale factors in addition to stand-scale factors.

     

Legacy effects of past land use on current biodiversity in a low-intensity farming landscape in Transylvania (Romania)

Context

Ecological impacts of past land use can persist for centuries. While present-day land use is relatively easy to quantify, characterizing historical land uses and their legacies on biodiversity remains challenging. Southern Transylvania in Romania is a biodiversity-rich area which has undergone major political and socio-economic changes, from the Austro-Hungarian Empire to two World Wars, communist dictatorship, capitalist democracy, and EU accession—all leading to widespread land-use changes.

Objectives

We investigated whether present-day community composition of birds, plants, and butterflies was associated with historical land use.

Methods

We surveyed birds, plants, and butterflies at 150 sites and classified those sites as forest, arable land, or managed grassland for six epochs using historical maps from the 1870s, 1930s, and 1970s, satellite imagery from 1985 to 2000, and field visits in 2012. Sites were labelled permanent if they had the same land use at all epochs and non-permanent otherwise. We used clustering and PERMANOVA based on community similarity to test for associations between community composition and land-use history.

Results

We found significant differences (p = 0.030) in bird communities between permanent and non-permanent forest sites, and permanent and non-permanent grassland sites (p = 0.051). No significant associations were found among plants or butterflies and land-use history.

Conclusions

Bird communities were associated with historical land use, though plants and butterflies were not. Historical land-use change in our study area was likely not sufficiently intense to cross relevant ecological thresholds that would lead to legacy effects in present-day plant and butterfly communities.

     

Leaf and seed yield of jute mallow (Corchorus olitorius L.) accessions under field conditions for two consecutive growing seasons

Jute mallow is a nutritious leafy vegetable used by many people in Africa. The purpose of this study was to select accessions with high leaf yield and seed yield. We investigated seven agronomic traits that are related to leaf yield and seed yield and how they correlate with each other. The results indicated significant differences among the accessions in all traits. Leaf fresh weight ranged from 18.3 to 121.3 g/plant in accessions TOT 6747 and TOT 8532, respectively. The highest variability between the accessions was also observed in seed yield. It ranged from 1.0 g/plant in accession TOT 7980 to 35.5 g/plant in TOT 7866. Eight other accessions had a seed yield of 1.0 g/plant. Significant and positive correlations were observed between leaf fresh weight and leaf dry weight (r = 0.84), leaf area (r = 0.33), and number of leaves (r = 0.40). A significant correlation was observed in seed yield and weight of pods per plant (r = 0.83). The evaluation of these agronomic traits for leaf and seed yield in this germplasm has revealed useful information for breeders in their efforts to improve the yield as well as selection of accessions with good agronomic traits.     

Comparing the landscape level perceptual abilities of forest sciurids in fragmented agricultural landscapes*

Perceptual range is the maximum distance from which an animal can perceive the presence of remote landscape elements such as patches of habitat. Such perceptual abilities are of interest because they influence the probability that an animal will successfully disperse to a new patch in a landscape. Furthermore, understanding how perceptual range differs between species may help to explain differential species sensitivity to patch isolation. The objective of this research was to assess the perceptual range of eastern chipmunks (Tamias striatus), gray squirrels (Sciurus carolinensis), and fox squirrels (Sciurus niger) in fragmented agricultural landscapes. Animals were captured in remote woodlots and translocated to unfamiliar agricultural fields. There they were released at different distances from a woodlot and their movements towards or away from the woodlot were used to assess their ability to perceive forested habitat. Observed perceptual ranges of approximately 120 m for chipmunks, 300 m for gray squirrels, and 400 m for fox squirrels, suggest that differences in landscape-level perceptual abilities may influence the occurrence of these species in isolated habitat patches.     

Effect of partial or total replacement of forage fish by a dry diet on the quality of reproduction in pikeperch, Sander lucioperca

The aim of this preliminary study was to evaluate the influence of different feeding regimes on the quality of reproduction in pikeperch. Three diets were tested: forage fish (FF), a commercial dry feed (DD) and a mix of both (FD).  The diets were given to fish throughout a complete reproductive cycle. During the spawning season, couples were injected with human chorionic gonadotropin (hCG) and let to spawn on nests. Proportion of running males, spawning and hatching success and larval quality (weight, length, body protein, total lipid, fatty acid and lipid class compositions and resistances to osmotic shock and starvation stress tests at hatching) were evaluated. The proportion of running male was lower in the DD group than in the FF and FD groups (54% for DD against 76–89% for FF and FD). In addition, 25%, 62.5% and 75% of injected couples gave spawning that hatched in DD, FF and FD groups respectively. Larval quality parameters were not significantly different between treatments. The results indicate that overall quality of reproduction was higher in FF and FD treatments than in DD. It suggests that the dry feed used was not totally adequate for pikeperch reproduction. Relations between breeder reproductive performances and the feed compositions are discussed.     

Ecosystem controls of juvenile pink salmon (Onchorynchus gorbuscha) and Pacific herring (Clupea pallasi) populations in Prince William Sound,Alaska

Five years of field, laboratory, and numerical modelling studies demonstrated ecosystem‐level mechanisms influencing the mortality of juvenile pink salmon and Pacific herring. Both species are prey for other fishes, seabirds, and marine mammals in Prince William Sound. We identified critical time‐space linkages between the juvenile stages of pink salmon and herring rearing in shallow‐water nursery areas and seasonally varying ocean state, the availability of appropriate zooplankton forage, and the kinds and numbers of predators. These relationships defined unique habitat dependencies for juveniles whose survivals were strongly linked to growth rates, energy reserves, and seasonal trophic sheltering from predators. We found that juvenile herring were subject to substantial starvation losses during a winter period of plankton diminishment, and that predation on juvenile pink salmon was closely linked to the availability of alternative prey for fish and bird predators. Our collaborative study further revealed that juvenile pink salmon and age‐0 herring exploit very different portions of the annual production cycle. Juvenile pink salmon targeted the cool‐water, early spring plankton bloom dominated by diatoms and large calanoid copepods, whereas young‐of‐the‐year juvenile herring were dependent on warmer conditions occurring later in the postbloom summer and fall when zooplankton was composed of smaller calanoids and a diversity of other taxa. The synopsis of our studies presented in this volume speaks to contemporary issues facing investigators of fish ecosystems, including juvenile fishes, and offers new insight into problems of bottom‐up and top‐down control. In aggregate, our results point to the importance of seeking mechanistic rather than correlative understandings of complex natural systems.     

Reproductive cycle of the Amazonian planktivorous catfish Hypophthalmus marginatus (Siluriformes,Pimelodidae)

We evaluated the annual process of oocyte and ovarian development of the planktivorous Amazonian catfish, the mapará (Hypophthalmus marginatus), aiming to support captive reproduction for domestication. A total of 149 females were captured from the Tocantins River at the Tucuruí Dam (3°49'55"S, 49°39'9"W) in 13 sampling events. For each individual, we evaluated ovary histology and plasma steroid concentrations. Two annual reproductive cycles, with similar characteristics, including a long period of rest, a short vitellogenic stage and a well‐defined spawning season from November to March, were described. A 17β‐estradiol (E₂) rise and a 17α,20β‐dihydroxy‐4‐pregnen‐3‐one (DHP) peak were associated with vitellogenesis and spawning season, respectively, in the first cycle but not in the second reproductive cycle. In conclusion, the studied species presents a reproductive cycle similar to that of other migratory total spawners; however, unusually for this group of fish, there were three (but not two) batches of vitellogenic oocytes in “in maturation” and “mature” stage ovaries, pointing to the possibility of more than one spawn during the spawning season.     

Osmoregulatory and endocrine relationships with chloride cell morphology and density during smoltification in coho salmon (Oncorhynchus kisutch)

Chloride cell morphology and density in the gill and opercular membrane of coho salmon (Oncorhynehus kisutch) were examined during the 1982 and 1983 smolt-seasons for structural correlates to smoltification-associated changes in hypoosmoregulatory ability and plasma hormone levels. Although not synchronous in the two years, plasma thyroxine levels displayed two peaks each year. In 1982, changes in gill Na⁺,K⁺-ATPase activity were preceded by elevations in plasma thyroxine. In 1983, the increase in enzyme activity corresponded with the April increases in plasma thyroxine and prolactin. Seawater (SW) acclimation experiments showed discrete increases in SW tolerance which coincided with changes in gill enzyme activity. Although these data suggest a relationship between SW tolerance and plasma thyroxine levels, the patterns in the two years were different. A significant peak in plasma prolactin levels in April suggests possible involvement in the parr-smolt transformation.

Chloride cells were studied in the opercular membrane, a chloride cell-containing epithelium lining the branchial side of the operculum, and the gill epithelium. Opercular membrane chloride cells (1982), marked with a mitochondrion-specific fluorescent stain, increased nearly two-fold in late May, concurrent with the second increase in gill Na⁺,K⁺-ATPase activity and SW tolerance. Gill morphology was examined (1983) with scanning and transmission electron microscopy and light microscopy. Initially, the gill filament surface appeared rough but became smoother during smoltification and rough again toward the end of smoltification. Two mitochondrion-rich (chloride) cell types were present in the gill epithelium during smoltification. The electron-lucent type I cell contained large, circular mitochondria while the electron-dense type II cell contained thin, elongate mitochondria. Ultrastructurally, many type I cells appeared disrupted which may indicate cellular degeneration or a special response of type I cells to fixation. However, it was unusual to find either intact or disrupted type I cells after March. Chloride cell density (type I plus type II) remained constant during smoltification. The inability to distinguish between these cell types with the light microscope may have obscured changes in their individual densities. The data from both the opercular membrane and the gill epithelium and their relationship with gill Na⁺,K⁺-ATPase activity suggest that the development of SW tolerance during smoltification is partially due to changes in chloride cell enzyme activity and density. The presence of two mitochondrion-rich cell types is discussed with regard to their possible role in the hypoosmoregulatory changes which occur during smoltification.     

Analysis of the impact of trap-neuter-return programs on populations of feral cats

OBJECTIVE: To evaluate 2 county trap-neuter-return (TNR) programs for feral cat population management via mathematical modeling. DESIGN: Theoretical population model. ANIMALS: Feral cats assessed from 1992 to 2003 in San Diego County, California (n = 14,452), and from 1998 to 2004 in Alachua County, Florida (11,822). PROCEDURE: Data were analyzed with a mathematical Ricker model to describe population dynamics of the feral cats and modifications to the dynamics that occurred as a result of the TNR programs. RESULTS: In both counties, results of analyses did not indicate a consistent reduction in per capita growth, the population multiplier, or the proportion of female cats that were pregnant. CONCLUSIONS AND CLINICAL RELEVANCE: Success of feral cat management programs that use TNR can be monitored with an easily collected set of data and statistical analyses facilitated by population modeling techniques. Results may be used to suggest possible future monitoring and modification of TNR programs, which could result in greater success controlling and reducing feral cat populations.