Seasonal variation in microhabitat of salamanders: environmental variation or shift of habitat selection?

<p>Demographic heterogeneity can have big effects on population dynamics, but for most species we have limited understanding of how and why individuals vary. Variation among individuals is of particular importance for stage-structured populations, and/or where species have ‘complex life-cycles’. This is especially relevant in the case of amphidromous fishes that typically spawn in river mouths and estuaries, develop at sea and return to freshwater to finish development. These fish face strong selection pressures as they negotiate challenges around dispersal and development in order to reproduce successfully. Quantifying variation amongst individual fish can improve understanding of their population dynamics and suggest possible drivers of variation. I evaluate patterns and sources of variation in demographic attributes of the New Zealand smelt (Retropinna retropinna). R. retropinna is an amphidromous fish that is endemic to New Zealand. While most populations have a sea-going larval stage, a number of landlocked freshwater populations occur, with the largest landlocked population residing in Lake Taupo. Here R. retropinna are presented with a variety of littoral feeding/spawning habitats and environmental conditions that may vary across distinct regions of the lake. In addition, the protracted spawning period for this species in Lake Taupo (occurring over eight months of the year) provides additional scope for seasonal variation to influence demographic attributes of individuals. I sampled R. retropinna from discrete coastal habitats (beach or river) that were located in the eastern, southern and western regions of the lake. I evaluated patterns of variation in the size-structure, age-structure and morphology of R. retropinna among habitats and/or regions across Lake Taupo. I used otoliths to reconstruct demographic histories (ages, growth rates, hatch dates) of individuals, and used a set of statistical models to infer spatial variation in demographic histories. I found differences in size and age structure between regions, and a temporal effect of hatch date on larval/juvenile growth rates. In addition, I obtained samples of R. retropinna from a sea-going population at the Hutt river mouth (sampled fish were presumed to be migrating upstream after their development period in Wellington Harbour and/or adjacent coastal environments). While Lake Taupo is large, deep, fresh, oligotrophic and strongly stratified for 8-9 months outside of winter, Wellington Harbour is less than a sixth of the area, shallow, saline, eutrophic and never stratified. These greatly differing environmental conditions led me to expect that these systems’ R. retropinna populations would carry significantly different demographic attributes. I compared the hatching phenology, recruitment age, body morphology, and individual growth histories (reconstructed from otoliths) of R. retropinna sampled from Lake Taupo and Wellington Harbour. I explored the relationships between demographic variation and environmental variation (water temperature, chlorophyll a) for the two systems and found that this additional environmental information could account for much of the seasonal variation in daily otolith increment widths of R. retropinna. My results also suggest that while the two sampled populations likely share similar hatching and spawning phenologies, individuals from Lake Taupo tend to grow more slowly, particularly during winter, and end up smaller than sea-going fish sampled near Wellington. I speculate that these differences reflect variation in food supply (zooplankton may be limited in Lake Taupo over winter). Overall, my results demonstrate a high degree of variation in morphological and life-history traits within a single species, potentially driven by an interaction between environmental variation and timing of development. My work contributes to a growing body of literature on demographic heterogeneity, and may help to inform the management of landlocked populations of R. retropinna in Lake Taupo.</p>

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Seasonal variation in the habitat associations of Atlantic cod (Gadus morhua) and American plaice (Hippoglossoides platessoides) from the southern Gulf of St. Lawrence

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f98-122 ◽

1998 ◽

Vol 55 (12) ◽

pp. 2548-2561 ◽

Cited By ~ 36

Author(s):

D P Swain ◽

G A Chouinard ◽

R Morin ◽

K F Drinkwater

Keyword(s):

Seasonal Variation ◽

Habitat Selection ◽

Gadus Morhua ◽

Atlantic Cod ◽

Statistical Significance ◽

Habitat Associations ◽

Practical Implications ◽

Hippoglossoides Platessoides ◽

Trawl Surveys ◽

Selection Of

We compared habitat associations of southern Gulf of St. Lawrence Atlantic cod (Gadus morhua) and American plaice (Hippoglossoides platessoides) between the summer feeding season on the Magdalen Shallows and the overwintering period in the Cabot Strait. Data were from bottom trawl surveys conducted in September 1993, 1994, and 1995 and January 1994, 1995, and 1996. Both species occupied much deeper, warmer water in winter than in summer. The effect of cod age on temperature distribution reversed between the two seasons, with younger cod occupying warmer water than older cod in summer and colder water in winter. Selection of both depth and temperature by cod tended to be more significant in September than in January. The reduced statistical significance of habitat selection by cod in winter was associated with a more aggregated distribution in this season. The contrast between seasons in habitat associations was particularly strong for plaice. The median habitats occupied by plaice were 58-67 m and -0.1 to 0.3°C in September and 374-426 m and 5.2-5.4°C in January. Habitat selection by plaice was significant in both seasons, but significance tended to be greater in January. Degree of aggregation in plaice distribution was similar between the two seasons. Female plaice occupied significantly warmer water than males in September but not in January. The ecological and practical implications of this striking seasonal variation in habitat associations are discussed.

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Seasonal Variation in Habitat Selection by Free-Ranging Feral Horses Within Alberta’s Forest Reserve

Rangeland Ecology & Management ◽

10.2111/rem-d-12-00081.1 ◽

2013 ◽

Vol 66 (4) ◽

pp. 428-437 ◽

Cited By ~ 11

Author(s):

Tisa L. Girard ◽

Edward W. Bork ◽

Scott E. Nielsen ◽

Mike J. Alexander

Keyword(s):

Seasonal Variation ◽

Habitat Selection ◽

Forest Reserve ◽

Feral Horses ◽

Free Ranging

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Diet and habitat-niche relationships within an assemblage of large herbivores in a seasonal tropical forest

Journal of Tropical Ecology ◽

10.1017/s0266467412000302 ◽

2012 ◽

Vol 28 (4) ◽

pp. 385-394 ◽

Cited By ~ 20

Author(s):

Farshid S. Ahrestani ◽

Ignas M. A. Heitkönig ◽

Herbert H. T. Prins

Keyword(s):

Seasonal Variation ◽

Habitat Selection ◽

South India ◽

Niche Breadth ◽

Niche Overlap ◽

Dry Season ◽

Wet Season ◽

Large Herbivores ◽

Axis Axis ◽

Habitat Niche

Abstract:There is little understanding of how large mammalian herbivores in Asia partition habitat and forage resources, and vary their diet and habitat selection seasonally in order to coexist. We studied an assemblage of four large herbivores, chital (Axis axis), sambar (Cervus unicolor), gaur (Bos gaurus) and Asian elephant (Elephas maximus), in the seasonal tropical forests of Bandipur and Mudumalai, South India, and tested predictions regarding the species’ seasonal diet browse : graze ratios, habitat selection and habitat-niche preference and overlap. Field data collected for the study included the seasonal variation in grass quality, the seasonal variation in δ13C in the species’ faeces and the seasonal variation in the species’ habitat selection and overlap using a grid-based survey. Results of the δ13C analyses showed that the chital was more of a grazer in the wet season (−17.9‰ to −21.6‰), but that it increased the proportion of browse in its diet in the dry season (−25.6‰ to −27.7‰); the gaur was a grazer for most of the year (−15.3‰ to −18.6‰); the sambar preferred to browse throughout the year (−21.1‰ to −30.4‰); and that the elephant was a mixed feeder (−14.2‰ to −21.4‰). Elephant habitat-niche breadth was high (0.53 in wet and 0.54 in dry) and overlapped equally with that of the other species in both seasons (0.39–0.94). The gaur had the most restricted habitat-niche breadth in both seasons (0.25 in wet and 0.28 in dry), and it switched from the moist deciduous habitat in the dry season to the dry deciduous habitat in the wet season. These results offer the first insights into the seasonal variation in browse : graze diet ratios and the habitat-niche overlap amongst the common largest-bodied mammalian herbivore species found in South India.

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Seasonal variation in habitat selection for a Neotropical migratory songbird using high‐resolution GPS tracking

Ecosphere ◽

10.1002/ecs2.3421 ◽

2021 ◽

Vol 12 (3) ◽

Author(s):

Calandra Q. Stanley ◽

Michele R. Dudash ◽

Thomas B. Ryder ◽

W. Gregory Shriver ◽

Kimberly Serno ◽

...

Keyword(s):

Seasonal Variation ◽

High Resolution ◽

Habitat Selection ◽

Gps Tracking ◽

Selection For ◽

Migratory Songbird

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