Successive Extinctions Research Articles

Contrasting population trends at seabirds colonies: is food limitation a factor in Norway?

Norwegian Northern Gannet Morus bassanus populations exhibit contrasting trends on a regional scale, with several colony extinctions having occurred in recent decades. In an attempt to understand the ecological drivers of such variability, we tested whether resource availability is a factor limiting the current development of gannetries in the Lofoten/Vesteralen area. Between 2007 and 2010, we recorded arrival and departure times of breeding Northern Gannets from two colonies from regions showing contrasting population growth rates during the past two decades. We also recorded the duration of joint attendances by Northern Gannet parents at the nest, performed opportunistic diet sampling and counted numbers of occupied nests. Finally, we compiled ring recoveries over a 30-year period to assess inter-colony movements. Norwegian Gannet parents spent more time together, attending their chick, and performed shorter foraging trips than those in British and French colonies of similar size. This suggests that, despite some annual variations, their foraging effort was relatively low. Diet samples from both colonies mainly constituted fish of high energetic value, such as large herring Clupea harengus, mackerel Scomber scombrus, and saithe Pollachius virens, prey that are relatively abundant within the study area. Data from ringed birds revealed a northward movement of adults ringed as breeding birds and chicks from extinct Lofoten colonies that established a growing colony close to the North Cape. Recorded foraging features (trip duration, joint attendance and prey quality) during our study does not indicate food availability as a limiting factor explaining successive extinctions and re-colonisations of breeding sites in Lofoten/Vesteralen. White-tailed Eagles Haliaeetus albicilla are known to predate opportunistically on Northern Gannet adults or chicks and their populations are growing in the Lofoten area. Their potential impact on the Norwegian Northern Gannet population dynamics should be further investigated.

Stability Analysis of Injection-Locked Multimode Oscillators

This paper presents an in-depth stability analysis of injection-locked multimode oscillators. The various types of bifurcations, or qualitative stability changes, occurring in these systems when varying the input power are studied in detail. It is shown that, for low injection power, each stable injection-locked oscillation coexists with as many two-fundamental quasi-periodic solutions as the number of stable periodic oscillations in the original free-running circuit. The mechanisms leading to the successive extinctions of these undesired stable quasi-periodic solutions are investigated in-depth, as well as the possible stabilization of periodic oscillation modes that were originally unstable in free-running conditions. The overall study enables a thorough understanding and anticipation of the complex nonlinear dynamics of these multimode systems. It is demonstrated that, by changing the injection frequency, together with control of the bias voltage, it is possible to switch between the various injection-locked oscillations, obtaining a reconfigurable system. The study is illustrated through application to a demonstrator, consisting of a ring oscillator in which six stable oscillation modes were measured at different operation points and frequencies comprised between 9.4 and 15.4 GHz.

Successive extinctions of muricate planktonic foraminifera (Morozovelloides and Acarinina) as a candidate for marking the base Priabonian

Successive extinctions of muricate planktonic foraminifera (Morozovelloides and Acarinina) as a candidate for marking the base Priabonian

Twinkling lights or turning down the dimmer switch? Are there two patterns of extinction debt in fragmented landscapes?

The decline and local extinction of many woodland birds across southern Australia is continuing and seems likely to continue for a long time even though broad-scale clearing has ceased in many regions. The small proportion of remaining vegetation and its fragmented and degraded nature will probably mean that a long-term extinction debt will have to be paid. For some species this will be through the process of successive extinctions of sub-populations and lack of recolonization due to poor dispersal ability, leading to ultimate extinction of the metapopulation. However, many bird species in Australia travel locally and regionally to exploit resources that vary in time and space (rich-patch nomads), and appear to be quite capable of dispersing in fragmented landscapes. Many of these too are declining and we need to understand the processes involved in their decline. Making the matrix more hospitable may reverse the declines of the poor dispersers. However, a different approach may be needed to assist the rich-patch nomads, such as re-establishing key resources. This will involve a better understanding of their natural history.

Faut-il avoir peur des introductions d'espèces ?

Should we be afraid of species introduction ? The question of the introductions of species often suffers from exaggerated fears of security and from hasty generalizations. With the concepts of balance and stability of the ecosystems, a static vision of nature was established. Now it is clear that populations proceed by invasions and successive extinctions, with some cases of spectacular, but cyclical proliferations. The author decides to demonstrate that there is no typical profile of invasive species, but that the resilience of the ecosystem, in its current climatic context, is only in question.

Food-web interactions govern the resistance of communities after non-random extinctions.

Growing concern about how loss of biodiversity will affect ecosystems has stimulated numerous studies. Although most studies have assumed that species go extinct randomly, species often go extinct in order of their sensitivity to a stress that intensifies through time (such as climate change). Here we show that the consequences of random and ordered extinctions differ. Both depend on food-web interactions that create compensation; that is, the increase of some species when their competitors and/or predators decrease in density due to environmental stress. Compensation makes communities as a whole more resistant to stress by reducing changes in combined species densities. As extinctions progress, the potential for compensation is depleted, and communities become progressively less resistant. For ordered extinctions, however, this depletion is offset and communities retain their resistance, because the surviving species have greater average resistance to the stress. Despite extinctions being ordered, changes in the food web with successive extinctions make it difficult to predict which species will show compensation in the future. This unpredictability argues for 'whole-ecosystem' approaches to biodiversity conservation, as seemingly insignificant species may become important after other species go extinct.

Cues to Decreasing Resistance to Extinction in Successive Acquisitions and Extinctions

Four groups of rats were used in a successive acquisition and extinction situation to determine which conditions, if any, produce a decrease in resistance to extinction across successive acquisitions and extinctions. Two groups experienced long N-R transitions (time from extinction to the subsequent acquisition) with all remaining transitions being short. The short transitions were: R-R (time between acquisition trials), R-N (time from the end of an acquisition until the subsequent extinction), and N-N (time between extinction trials). Two groups experienced long R-N and short N-R, N-N, and R-R transitions. Rats in one long N-R transition and one long R-N transition group had acquisitions and extinctions delineated by distinctive cues (blinking lights during acquisition or extinction trials). The other two groups had no such cues. The disparity in N-N versus N-R transition times combined with additional visual cues during extinction produced decreasing resistance to extinction across successive extinctions.

BEHAVIOR CHANGES DURING REPEATED EIGHT‐DAY EXTINCTIONS1

Pigeons were given repeated two-day conditionings alternating with eight-day extinctions using a trial procedure. One group had different key colors during each of the first five conditioning-extinction pairs; another group had the same key color throughout. Total extinction responses of both groups were quite constant over successive extinctions. This finding differs from the rapid declines found in most previous studies with bar-press and key-peck responses. The difference probably was due to our longer extinctions, because responses early in each extinction did decrease. However, that decrease was neutralized by increases in responses late in each extinction. The two opposite changes indicate the influence of two different factors during repeated extinctions, with neither factor having much stimulus specificity. The reduction of early responses may result from feeding changes confounded with extinction. The increase in later extinction responses may result from a decrease in the effect of unreinforced responses after their repeated occurrence.

Successive Acquisitions and Extinctions with Goldfish (Carassius Auratus) in a Swimway Situation

Goldfish were trained in a successive acquisition and extinction shuttle-swimway situation. Groups of 12 fish experienced alternating days of acquisition and extinction, extinction following immediately after each daily acquisition session, and acquisition following immediately after each daily extinction session. None of the groups produced decreasing resistance to extinction across extinctions within eight successive acquisitions and extinctions. A group of fish given 16 successive acquisitions and extinctions with alternating days of acquisition and extinction learned to decrease swimming speeds after eight successive extinctions. However, these fish also decreased acquisition speeds across the last 8 successive acquisitions.

The effects of overtraining and successive extinctions upon nictitating membrane conditioning in the rabbit

In Expt. I Group SAE ( N = 16) received four successive acquisitions and extinctions of a classically conditioned nictitating membrane response while Group OTC ( N = 8) received an equivalent amount of acquisition training followed by a single extinction session. Successive extinctions resulted in a decrease in resistance to extinction (Rn), but extended acquisition training had no significant effect. In Expt. II a total of 96 subjects participated in a factorial study of the effects of various amounts of overtraining at two different UCS intensities. When CR amplitude was asymptotic extended training had no significant effect upon Rn; when amplitude was below asymptote Rn was correspondingly reduced.

Determinants of rate of extinction in successive acquisitions and extinctions

Rats were used in an investigation of the conditions that are necessary to obtain a decrease in resistance to extinction across extinctions in a successive acquisition and extinction paradigm. Long breaks (23.5 h) after extinction coupled with a short intertrial interval within extinction sessions (long N-R transition) resulted in a decrease in resistance to extinction across the successive extinctions. Long breaks after acquisition sessions (long R-N transition), or in the middle of acquisition sessions (long R-R transition), yielded an increase in resistance to extinction across the successive extinction sessions. When extinction sessions followed immediately after acquisition sessions (N-R), Ss decreased their running speeds within each of the successive extinctions. When acquisition sessions followed immediately after extinction sessions (R-N), Ss decreased their running speeds within the first few successive extinctions. The R-N Ss learned to increase their running speed within extinctions during the later successive extinctions.

A reexamination of extinction rate in successive acquisitions and extinctions.

A reexamination of extinction rate in successive acquisitions and extinctions.

Effect of reserpine administered during infancy on brain catecholamines and adult behaviour in the rat.

SUMMARYReserpine (0.1 mg/kg/day) was administered to rats from 11 through 30 days of age. During and after administration of reserpine, concentrations of catecholamines, epinephrine and norepinephrine, in the brain were estimated. Levels of catecholamines were about 30 per cent of normal during the period of reserpine administration. Approximately 3 weeks were required for these levels to return to normal. When animals were 95‐100 days of age, they were deprived of food and were trained to press a bar for food. When the rate of responding became stable, the animals were subjected to three successive extinctions at daily intervals and the increase in response rate after the onset of each extinction was determined. This extinction‐induced increase in response rate was greater for previously reserpinized animals than controls during the second and third extinctions, but not the first. These findings are interpreted as a decreased ability of the animals, reserpinized during infancy, to learn to respond discriminatively during non‐reinforcement (extinction). Thus, an effect of reserpine administration during infancy on a type of behaviour in the adult has been demonstrated. This occurs after the catecholamine‐depleting effect of the reserpine has been fully dissipated.

Successive acquisitions and extinctions of an instrumental response.

Successive acquisitions and extinctions of an instrumental response.

Successive Extinctions of a Bar-Pressing Response in Rats

Successive Extinctions of a Bar-Pressing Response in Rats