Demography of the land snail Tikoconus (Tikoconus) costarricanus (Stylommatophora: Euconulidae) in tropical low montane and premontane forests, Costa Rica

Abstract

Abstract. Introduction: Ecology and natural history of neotropical land snails is almost unknown. Objetive: In this paper I analyse the population dynamics of Tikoconus (Tikoconus) costarricanus Barrientos, in prep., an understory endemic euconulid. Methods: I compared T. costarricanus’ demography patterns in tropical montane forests in central Costa Rica in three habitats with different restoration techniques: a mature forest, a secondary forest and a Cuppressus lusitanica plantation. I collected data in three month periods during a year. I analysed population size in relation with habitat, sampling date, leaf litter humidity, depth and quantity; and specimen size in relation with habitat and sampling date. I also kept some specimens in terraria and described part of their natural history. Results: The species is more abundant in mature forest (Ø = 0.174 ind/m2). The number of specimens in each habitat was constant throughout the year (Kruskall-Wallis = 2.0118, p = 0.57, NS) and hatching occurs in the middle and last months of the rainy season (Kruskall-Wallis = 17.3061, p = 0.00061, **). Number of specimens is related with leaf litter humidity (Spearman correlation, r = 0.3524, n = 232, p = 0.000, **), amount (Spearman correlation, r = 0.3922, n = 232, p = 0.000, **) and depth (Spearman correlation, r = 0.2543, n = 232, p = 0.000, **). This relationship is explained by the high and stable humid environment provided by leaf litter. During the drier months some specimens migrate from the foliage to the leaf litter. Eggs (Ø = 1mm) are laid on moss or soil and the young spend the first 2 or 3 weeks of their life on moss. Egg masses are small (Ø = 4 eggs), and shells look bubbly. Egg development time (20 days) was longer than in other tropical species. Adult pigmentation appears around two months after hatch. In the only case observed egg laying began 5 months after hatching and the specimen lived 9 months. Conclusions: Although no conclusive, these data point to a fragile species susceptible to habitat and climate change. Restorations techniques should consider leaf litter features in order to protect endemic neotropical humid dependent diversity.

Selección de microhábitat, y actividad diaria y estacional del caracol Tikoconus costarricanus (Stylommatophora: Euconulidae) en el sotobosque de bosques tropicales húmedos de montaña.

“…In contrast to most land snails, the neotropical snail T. costarricanus has the same abundance throughout the year, is active at any time of the day or night and spends most of time on leaves (Barrientos, 2019b). However, some of its behaviors and preferences are seasonal and also vary along the day.…”

“…Many active T. costarricanus snails seem to avoid leaves´ upper side, even though food is more abundant there and their pigmentation help them camouflage with epiphytes, suggesting that there are difficulties on this side of the leaves (Barrientos, 2019b(Barrientos, , 2020. Besides this, snail frequency on the upper side of leaves changes with season and daytime.…”

“…Water surface tension of drops may trap and drown snails, but also drops´ kinetic energy may throw the snail from the leaves into the leaf litter. If this happens, they may: 1) fall into a flooded area and drown; 2) fall on leaf-litter that has lost their protection function against predators and weather due to rainfall compaction effect; T. costarricanus has been found in the leaflitter only during the dry season (Barrientos, 2012(Barrientos, , 2019b; or, 3) have to spend extra energy to get back onto the leaves where they feed. Therefore, when water drops may fall, it is more convenient to stay in a protected place, in this case, the closest rain protected spots are leaves´ underside (Pesquero, Corrêa, Pesquero, & de Paula, 2014).…”

“…All specimens considered were adults or sub adults with a well pigmented cephalopodium and a shell diameter of 3.5 mm or more (Barrientos, 2019b). Whenever I found an individual I observed the specimen for less than 15 s, disturbing it as little as possible and took note of: season, time, activity, behaviour, temperature and relative moisture inside the forest (only during dry season samplings due to logistic problems), part of the leaf, plant height (five categories: 0-0.5 m, 0.6-1.0 m, 1.1-1.5 m, 1.6-2.0 m, 2.1-2.5 m) and weather.…”

“…In arid Mediterranean regions the choice is regulated by humidity and temperature, but in humid places only temperature is meaningful (Moreno-Rueda et al, 2009). However, other researchers state that litter moisture and litter level, shading, ground water level and abundance of some plants are also important in microhabitat selection (Willig, Sandlin, & Gannon, 1998;Barrientos 2000;Książkiewicz, Kiaszewicz, & Gotdyn, 2013;Barrientos 2019b). Regarding microhabitat selection of tropical arboreal snails, Hernández-Quinta (2013) found that most Cuban species prefer branches and trunks, although some species can be found on leaves, except for Jeanneretia bicinta which is restricted to leaves.…”