The Unexpected Presence of Elysia chlorotica (Gould, 1870) in Tampa Bay, Florida, U.S.A. with Notes on Seasonal Population Decline

The Unexpected Presence of Elysia chlorotica (Gould, 1870) in Tampa Bay, Florida, U.S.A. with Notes on Seasonal Population Decline

Suitability modelling and mapping methods were developed to predict spatial distributions and population abundance of fish and macroinvertebrate species in Florida estuaries and coastal zones. Habitats were mapped in Pensacola Bay, Tampa Bay, and Charlotte Harbor using data from fisheries‐independent monitoring. Starting in 1997, suitability functions from habitat suitability index models were linked to habitat grids to create seasonal maps for early‐juvenile, juvenile, and adult life‐stages. After 2003, habitat suitability models (HSM) were linked to seasonal habitat grids to create seasonal maps validated by reciprocal transfer of suitability functions between estuaries. A quantitative method was used with five factor models and models with fewer environmental factors for four species in 2005 and for 11 species by life‐stages in 2009. In 2006, suitability functions transferred from Charlotte Harbor were linked with habitat grids for Rookery Bay and Fakahatchee Bay and HSM maps produced for three time periods to test transferability to estuaries lacking long‐term monitoring. Analyses in 2012 demonstrated that HSM maps for Tampa Bay derived independently from earlier suitability functions were almost identical to HSM maps created using recent suitability functions. Salinity was the most significant environmental variable for predicting abundance in models for species life‐stages in the Peace River and Charlotte Harbor, although nutrient concentrations from upriver may have influenced species’ abundances associated with low (<5 psu) to moderate (5–10 psu) salinities. Population abundance estimates for Charlotte Harbor were derived from seasonal HSM maps created in 2019 and 2021. The 2021 paper compared changes in seasonal population numbers between Baseline and Minimum Flows associated with projected water withdrawals from the Peace River. Electronic logbooks were developed in 2001 and 2004 to collect data on shrimp fishing vessels and HSM maps for the West Florida Shelf created for 16 months in 2004–2005. Methodologies evolved as enabling technology became available.

For declining wild populations, a critical aspect of effective conservation is understanding when and where the causes of decline occur. The primary drivers of decline in migratory and seasonal populations can often be attributed to a specific period of the year. However, generic, broadly applicable indicators of these season-specific drivers of population decline remain elusive. We used a multi-generation experiment to investigate whether habitat loss in either the breeding or non-breeding period generated distinct signatures of population decline. When breeding habitat was reduced, population size remained relatively stable for several generations, before declining precipitously. When non-breeding habitat was reduced, between-season variation in population counts increased relative to control populations, and non-breeding population size declined steadily. Changes in seasonal vital rates and other indicators were predicted by the season in which habitat loss treatment occurred. Per capita reproductive output increased when non-breeding habitat was reduced and decreased with breeding habitat reduction, whereas per capita non-breeding survival showed the opposite trends. Our results reveal how simple signals inherent in counts and demographics of declining populations can indicate which period of the annual cycle is driving declines.

The McKay’s Bunting (Plectrophenax hyperboreus) is endemic to Alaska, breeds solely on the remote and uninhabited St. Matthew and Hall islands (332 km2) in the central Bering Sea, and is designated as a species of high conservation concern due to its small population size and restricted range. A previous hypothesized population estimate (~2,800 to 6,000 individuals) was greatly increased (~31,200 individuals) after systematic surveys of the species’ entire breeding range in 2003, establishing McKay’s Bunting as one of the rarest passerines in North America. In 2018, we replicated the 2003 surveys and used density surface models to estimate breeding season densities, distributions, and population change over the intervening time period. Our results indicate that the McKay’s Bunting population declined by 38% (95% CI: 27 to 48%) from ~31,560 to 19,481 individuals since 2003. Spatial model predictions showed no areas with an increase of birds on either St. Matthew or Hall islands but revealed declines across 13% (42 km2) of St. Matthew Island. Declines disproportionately occurred both in marginal habitats with reduced rocky nesting substrate and in high-density hotspots along the coast of St. Matthew Island. The total area occupied by breeding adults decreased by 8%, and high-density hotspots shifted inland from the coast of St. Matthew Island to higher elevations on both islands, the latter potentially responses to exceptionally warm weather and reduced spring snow cover in 2018. Additionally, we observed low numbers of predators and interspecific competitors in 2018, suggesting that these did not cause the decline. Our findings indicate that McKay’s Bunting meets international standards for elevating its conservation status from Least Concern to Endangered based on the International Union for Conservation of Nature Red List of Threatened Species ranking criteria. Additional population monitoring and studies to identify the causal mechanisms of the recent population decline of this rare species could assist future population assessments.

Although food has been proposed as a possible factor on population regulation of small mammals, evidence of food restriction in field conditions is still lacking. Food restriction is generally thought to occur in high-density years of oscillating populations of small mammals. By using two body condition indices (muscle protein concentration and cleaned carcass index), we investigated variations of body condition of the greater long-tailed hamster (Tscherskia triton) and the striped hamster (Cricetulus barabensis) in the Raoyang County of the North China Plain during a population decline- and low-phase from 1998 to 2003. Our laboratory experiments showed that food restriction reduced muscle protein concentration and cleaned carcass index of greater long-tailed hamster. We found there were significant differences in body condition of hamsters over the six years. Both the muscle protein concentration and cleaned carcass index of T. triton were significantly and positively correlated with its yearly trap successes, which reflected yearly population densities. Muscle protein concentration of C. barabensis was positively correlated with the total yield of the wheat. This observation supported the hypothesis on the in-phase relation between food resources or availability and rodent abundances. During the four seasons, muscle protein concentration of two species was highest in autumn, and lowest in summer. These two body condition indices of wild T. triton in summer and in low phases were similar to 60% food restricted animals raised in the laboratory, but significantly lower than nonfood- restricted animals. Our results indicated that malnutrition occurred in summer when food was not abundant, and in low density years with low grain production (an index reflecting food abundance of rodents) in our study region. Therefore, we concluded that food limitation may play an important role in seasonal and inter-annual population fluctuation of these two hamster species.

Allee effects driven by predation can play a strong role in the decline of small populations but are conventionally thought to occur when generalist predators target specific prey (i.e. type II functional response). However, aside from direct consumption, fear of predators could also increase vigilance and reduce time spent foraging as population size decreases, as has been observed in wild mammals living in social groups. To investigate the role of fear on fitness in relation to population density in a species with limited sociality, we exposed varying densities of Drosophila melanogaster to mantid predators either during an experimental breeding season or non-breeding season. The presence of mantids in either season decreased the reproductive performance of individuals but only at low breeding densities, providing evidence for an Allee effect. We then used our experimental results to parametrize a mathematical model to examine the population consequences of fear at low densities. Fear tended to destabilize population dynamics and increase the risk of extinction up to sevenfold. Our study provides unique experimental evidence that the indirect effects of the presence of predators can cause an Allee effect and has important consequences for our understanding of the dynamics of small populations.

The field study investigates the seasonal incidence and population dynamics of the mustard aphid, Lipaphis erysimi (Kalt.), and its natural predator, Coccinella septempunctata Linn., on mustard (Brassica juncea L.) during the Rabi seasons of 2022–23 and 2023–24 at Research Farm of College of Agriculture, Sumerpur. The results revealed that aphid infestation commenced in the last week of December (52nd, SMW) and persisted until mid-March (10th SMW). The aphid population peaked in the 5th Standard Meteorological Weak (SMW) (137.90 aphids per plant) in 2022–23 and in the 6th SMW (138.40 aphids per plant) in 2023–24, coinciding with temperatures ranging from 11.9°C to 25.6°C and moderate relative humidity (36.1%–45.2%). Correlation analysis indicated a significant negative relationship between aphid population and temperature, while relative humidity exhibited a weak positive association. The predatory C. septempunctata population followed a similar trend, peaking in the 5th SMW (9.20 beetles per plant) in 2022–23 and the 6th SMW (9.35 beetles per plant) in 2023–24, with a strong correlation (r > 0.94) between predator and aphid densities. The findings confirm that temperature plays a crucial role in regulating aphid incidence, with higher temperatures (>30°C) leading to a sharp decline in population. The study highlights the potential of C. septempunctata as a biological control agent and emphasizes the importance of integrating weather-based pest forecasting models into sustainable pest management strategies.

Anthropogenic degradation of natural habitats is a global driver of wildlife population declines. Local population responses to such environmental perturbations are generally well understood, but in socially structured populations, interactions between environmental and social factors may influence population responses. Thus, understanding how habitat degradation affects the dynamics of these populations requires simultaneous consideration of social and environmental mechanisms underlying demographic responses. Here we investigated the effect of habitat degradation through commercial forestry on spatiotemporal dynamics of a group-living bird, the Siberian jay, Perisoreus infaustus, in boreal forests of northern Sweden. We assessed the interacting effects of forestry, climate and population density on stage-specific, seasonal life-history rates and population dynamics, using long-term, individual-based demographic data from 70 territories in natural and managed forests. Stage-specific survival and reproductive rates, and consequently population growth, were lower in managed forests than in natural forests. Population growth was most sensitive to breeder survival and was more sensitive to early dispersing juveniles than those delaying dispersal. Forestry decreased population growth in managed forests by reducing reproductive success and breeder survival. Increased snow depth improved winter survival, and warmer spring temperatures enhanced reproductive success, particularly in natural forests. Population growth was stable in natural forests but it was declining in managed forests, and this difference accelerated under forecasted climate scenarios. Thus, climatic change could exacerbate the rate of forestry-induced population decline through reduced snow cover in our study species, and in other species with similar life-history characteristics and habitat requirements.

I present data on the Mariana Crow for an extensive but previously unavailable set of population and habitat surveys from 1992 to 1993. From these, I (1) compute a series of population estimates from that period during which Mariana Crow numbers were first entering a precipitous decline, (2) quantitatively assess the habitats occupied by individual birds and thereby provide a view of the range of habitats occupied during a time when the species was still widespread, and (3) provide the first direct wet-dry season comparisons of populations and habitat occupancy. Surveys yielded significantly different wet (943) and dry season (459) population estimates, which suggested wet season courtship activity preceding dry season nesting when birds became more secretive. Moreover, they indicated that the critical turning point in population decline was after 1995. Forest was the principal habitat type occupied during both wet and dry seasons, with savanna present less than half as often as forest, although birds occupied a range of additional habitats. The species was more versatile in habitat use than is often assumed, as rates of habitat occupancy and availability were similar. Versatility is an advantage for populations confined to small islands that periodically suffer catastrophic habitat damage due to typhoons.

Capsule At both landscape and local scales, breeding persistence in a declining Hawfinch population was greatest where broadleaved woodland cover was high, while at a fine scale, nest sites were associated with openings in the woodland canopy.Aims To assess which components of habitat are associated with Hawfinch occupancy at landscape (10-km), local (tetrad) and fine (nest) spatial scales, during a period of population decline and range contraction.Methods Bird Atlas 2008–11 data were used to determine areas of Hawfinch loss and persistence over 20 years. Current habitat was measured and compared to look for correlates that helped explain the differing status at both 10-km and tetrad scales. Fine scale habitat data collected at nest sites were compared with random locations to investigate within-wood nest site selection.Results At both 10-km and tetrad scales, Hawfinch persistence is more likely where woodland cover is greater. Recent woodland management was less evident in tetrads where the species persisted. At the nest site scale, the only relationship detected was for nests to be close to canopy openings.Conclusions Maintaining and increasing broadleaved woodland area is likely to benefit Hawfinch. Within woods, maintenance and creation of open areas may enhance nesting opportunities.

Monitoring endangered wildlife is essential to assessing management or recovery objectives and learning about population status. We tested assumptions of a population index for endangered Laysan duck (or teal; Anas laysanensis) monitored using mark–resight methods on Laysan Island, Hawai'i. We marked 723 Laysan ducks between 1998 and 2009 and identified seasonal surveys through 2012 that met accuracy and precision criteria for estimating population abundance. Our results provide a 15-y time series of seasonal population estimates at Laysan Island. We found differences in detection among seasons and how observed counts related to population estimates. The highest counts and the strongest relationship between count and population estimates occurred in autumn (September–November). The best autumn surveys yielded population abundance estimates that ranged from 674 (95% CI = 619–730) in 2003 to 339 (95% CI = 265–413) in 2012. A population decline of 42% was observed between 2010 and 2012 after consecutive storms and Japan's Tōhoku earthquake-generated tsunami in 2011. Our results show positive correlations between the seasonal maximum counts and population estimates from the same date, and support the use of standardized bimonthly counts of unmarked birds as a valid index to monitor trends among years within a season at Laysan Island.

Investigations were carried out on the seasonal population fluctuations of the moth Cydia ptychora. The population increased from May to September and declined from November to April. Increasing temperatures and decreasing r.h. appeared to be associated with population decline, while the reverse seemed to favour population increase. From light trap catches, sex ratios of adults showed considerable variation from month to month. The overall ratio was 2:1, in favour of the males, but there was a tendency for adjustment towards an apparently female-biased ratio from March to August. Bracon (?) hancocki was found to be a major parasite. Other biotic factors contributing to population regulation included 13 hymenopterous parasites and three predators (Philodicus temerarius, Bactria sp. nr. guineensis and Chrysopa sp.)

ABSTRACTMottled ducks (Anas fulvigula) are endemic to the Gulf Coast of North America, and their range stretches from Alabama to the Laguna Madre of Mexico, with a distinct population in peninsular Florida and an introduced population in South Carolina. As one of the few non‐migratory ducks in North America, mottled ducks depend on a variety of locally available habitat throughout the annual cycle, and threats to these landscapes may affect mottled ducks more acutely than migratory species. Annual population monitoring has revealed declines in mottled duck populations in Texas and Louisiana since 2008, and the genetic integrity of the Florida population has been muddled by the presence of large numbers of feral mallards (Anas platyrhynchos) resulting in hybridization. Similar to other closely related dabbling ducks, mottled duck populations are influenced by recruitment and breeding season survival, so changes in these factors may contribute to population decline. Accordingly, researchers have attempted to address various aspects of mottled duck breeding season ecology and population dynamics since the 1950s. We conducted a literature review on this topic by searching a combination of key terms using Google Scholar, including mottled duck, nesting ecology, habitat use, breeding incidence, nest success, brood, and breeding season survival, and followed citation trees to eventually aggregate information from nearly 50 publications on mottled duck breeding ecology. Our review concluded that mottled ducks use brackish and intermediate coastal marsh, including managed impoundments, and agricultural land during the breeding season. Their nests can be found in pastures, levees, dry cordgrass marsh, cutgrass marsh, spoil banks, and small islands. Nesting propensity and nest success estimates are often lower than other waterfowl species that are characterized by stable or increasing populations. Broods use wetlands composed of a mix of open water with submerged and emergent vegetation. Breeding season survival is higher for the Florida population than the western Gulf Coast population, but adult survival in both geographies is comparable to (or higher than) that of other dabbling duck species. Breeding habitat use, breeding season survival, and nest‐site selection and success have been studied extensively in mottled ducks, whereas information on nesting propensity, renesting intensity, and post‐hatch ecology is lacking. © 2021 The Wildlife Society.

The Pismo clam (Tivela stultorum) has experienced substantial population decline in California over the past century, extinguishing most public participation in a once-iconic recreational fishery before the end of the 20th century. A subsequent decrease in data collection has led to uncertainty about the current population status of this species. We conducted 6 years of intertidal Pismo clam population assessment surveys in Orange, San Diego, and southern Los Angeles Counties to provide a current dataset that could help guide research and management efforts in southern California. Pismo clams were observed at 19 out of 27 study sites during 57 days of surveys. Average clam bed density was low (mean 2.0 ± 1.1 clams/m2, median 0.1 ± 0.7 clams/m2, n = 21 sites), especially when considering larger clams ≥ 35 mm (mean 0.3 ± 0.1 clams/m2, median 0.1 ± 0.4 clams/m2), and varied greatly between sites (0.0–98.5 clams/m2), with Orange County densities approximately one order of magnitude lower than those in San Diego County. Juvenile recruitment was generally low or undetectable, except for consistent recruitment within a < 10 km beach area in San Diego County and a much larger, widespread recruitment event in 2022. Multi-year observations at several sites failed to indicate any consistent seasonal or inter-annual population trends. Densities and abundances were similar to recent historic data (< 30 years old), but are substantially lower than populations prior to the 1980s. We conclude that the Pismo clam persists on many southern California beaches at generally low densities and that recruitment is occurring throughout the southern California region with high spatial and temporal variability. This study provides foundational data to help inform Pismo clam conservation management decisions and to which additional monitoring, ecological research, and fishery data collection should be added.

Two seasonal population peaks of Xiphinema americanum were observed in an ornamental spruce nursery. One cycle extended from April to August and the other from September to January. These peaks became less obvious in the larvae and non-gravid adult populations as sampling depths increased. The gravid adult population, however, showed two distinct cycles at all sampling depths. Large numbers of nemas became tesselated and transparent in July; this was followed by a sharp decline in the nematode population. Eggs and third and fourth stage larvae were apparently the only stages to survive winter temperatures; adults disappeared at all sampling depths from 0-50 cm even though the soil was never frozen below 33 cm and the temperature never dropped below 1° C at 46 cm. There appeared to be an antagonism between X. americanum and Criconemoides xenoplax since C. xenoplax declined and X. americanum increased in number in two ornamental blue spruce plantings.