Conceptual Frameworks and Methods for Advancing Invasion Ecology

Invasion ecology has much advanced since its early beginnings. Nevertheless, explanation, prediction, and management of biological invasions remain difficult. We argue that progress in invasion research can be accelerated by, first, pointing out difficulties this field is currently facing and, second, looking for measures to overcome them. We see basic and applied research in invasion ecology confronted with difficulties arising from (A) societal issues, e.g., disparate perceptions of invasive species; (B) the peculiarity of the invasion process, e.g., its complexity and context dependency; and (C) the scientific methodology, e.g., imprecise hypotheses. To overcome these difficulties, we propose three key measures: (1) a checklist for definitions to encourage explicit definitions; (2) implementation of a hierarchy of hypotheses (HoH), where general hypotheses branch into specific and precisely testable hypotheses; and (3) platforms for improved communication. These measures may significantly increase conceptual clarity and enhance communication, thus advancing invasion ecology.     

Predictable annual mass release of gametes by the coral reef sponge Neofibularia nolitangere (Porifera: Demospongiae)

Mass release of gametes of the sponge Neofibularia nolitangere (Duch. & Mich., 1864) occurs simultaneosly along the leeward coast of Curaçao over a period of three subsequent days, without any apparent spatial pattern in the sperad of activity. A population of 99 individual sponges was monitored from August through November 1984 for development and subsequent release of gametes. Release started every day of 3 3-d period (12 to 14 October) at about 1400 hrs and lasted until just after sunset (1830 hrs). Ninety percent of the population showed reproductive activity. Exactly one lunar month later (11 to 12 November), a second release of gametes occurred. In the following year the same sequence of events was observed for the original population (2 to 4 October and 1 to 2 November, 1985). In all instances the first gamete release began on the third day after the full moon. These and earlier observations on this phenomenon show a strong correlation between moon phase and the time of gamete release. Histological and field observations show separate development and release of gametes (sex-ratio males: females 1.5:1) with external fertilization. No sex-reversal occurred in the population during release activity the following year, demonstrating a clear gonochoristic and oviparous type of reproduction for N. nolitangere. First development of oocytes and spermatocytes has been observed at 36 and 7 d, respectively, before the date of first release. In both males and females, a major part of the mesohyl of the total sponge was involved in gamete development. Spermatozoa are released through the osculum as a dense white smoke; eggs consisting of oocyte-nurse cell globules, reinforced with spicules, are separately released en masse with the outgoing water stream of the female sponge. Shortly after release the eggs become sticky and show a negative buoyancy. The reproductive strategy of N. nolitangere appears to be directed at maximizing the number of surviving recruits by maintaining a high reproductive output at a short specific time interval.