Introduction
This database has been assembled to present source data on the autecology
of neotropical marine mollusks represented in the Panama Paleontology Project
collections of Middle Miocene to Recent age. Its scope includes all of
the gastropod and bivalve genera and subgenera identified to date in the
463 PPP mollusk collections which were databased and archived as the Mollusc
Occurrence 2000 database (1st March 2000) and subsequently filtered and
refined to produce an analyzable dataset: the ‘Occurrence 2000 database’
(archived.1st March 2000). Scaphopods, chitons and cephalopods, the last
two of which are very rare, have not been subject to any ecological analyses
and I have excluded them.
Approach
My overall approach has been to assess separately the life habits of bivalves
and gastropods and to consider those which are known or which can be reliably
inferred through functional morphology, or taxonomic uniformitarianism
in the case of anatomically unknown Recent or extinct taxa. I have undertaken
a literature search to establish life habits for taxa at the generic level.
Where life-habits are known to vary across subgenera of a genus I have
coded the habits separately for each subgenus. Holoplanktic forms have
been indicated as such and have been excluded from our ecological analyses
(Todd et al., in prep.), which are restricted to the benthos.
Scope of literature review
There is an abundant literature on benthic molluscan life habits but it
is very widely scattered through ecological, systematic and faunal works.
For each genus or subgenus I have tried to provide at least one reference
to a work which provides some, if not all, of the life habit information
coded. Additional information has been added where necessary -- from functional
morphological analysis or more general habitat preferences. The cited references
are not intended to be comprehensive, but are simply intended to support
my life habit assignations. They vary from primary literature on a particular
species or genus through to literature reviews of a particular lifestyle
or taxonomic group. I have chosen to include more general works when they
usefully summarise and serve as a bibliography to more detailed studies,
particularly when numerous works exist on a particular taxon. All literature
identifications have been assessed according to our current taxonomy, so
that a name used in a listed paper may not agree with the genus or subgenus
to which it is now referred in the PPP databases.
Coding of citations
I have tried to indicate the specificity with which the cited literature
refers to the taxon in question by using a capital letter code; A through
D. With caution, this may in some cases serve as a guide to the accuracy
of the assigned life habits.
A: Bibliographic reference applies to the genus, including different
subgenera (as interpreted in our in-house PPP systematics).
B: No data available for genus; reference is to a genus in same
subfamily or family (rarely superfamily) and which is believed, on functional
morphological or other grounds, to have similar life habits.
C: Reference to subfamily or family-level data when members
are believed to have uniform life habits, at least for taxon in question.
D: functional morphological interpretation only (bivalves).
Life habit variability
An individual may show distinct life habits through its post-larval (benthic)
ontogeny. Here I have coded taxa solely for their adult condition. Similarly,
within a species life habits of and between individuals may vary; where
known I have reflected this variability in the coding. At a higher taxonomic
level, individual species within a genus/subgenus may show a range of
life habits: this variation too is coded. However, there are exceptions,
where particular morphotypes within a genus/subgenus are known to have
distinct life habits, then I have coded for only those morphotypes represented
in our collections; an example is the limopsid bivalves.
Bivalve life habit categories
Over the past 30 years our understanding of bivalve ecology has been revolutionized
by the discovery of widespread chemautotrophs, carnivory, and recently
reported probable suctorial feeding. This diversity of trophic mechanisms
has put to rest the longstanding division into suspension and deposit feeding.
Paradoxically, we are now discovering that these last two categories are
in some cases at least not mutually exclusive (see below). Despite all
of this, Stanley’s pioneering work into the functional morphology of the
bivalve shell still holds up in demonstrating the strong correpondences
between a range of shell characters and life habits, thus permitting accurate
assessment of anatomically unknown Recent and extinct taxa.
I have followed Stanley (1972) in considering the major groups of life
habits to be: 1) organism/substrate relationship or life position; 2) feeding
type, and 3) mobility; from which I have separated another largely independent
category, 4) shell fixation. In each of these four groups I have identified
a range of states, 19 in total, which are largely distinct and, with the
exception of relative mobility, can mostly be directly ascertained from
shell morphology. I have recognised a larger number of potentially discrete
life habit combinations than did Stanley in his study of shallow shelf
bivalves (he also excluded the largely commensal Galeommatoidea from consideration:
I have tried to include them here). Even allowing for the huge increase
in knowledge, I have found the range of bivalve life habits to be inadequately
characterised by Stanley’s very broad guilds. The data presented here allows
analyses to be conducted down to individual life habit level.
Organism/Substrate Relationships
ER: epifaunal recliner
Bivalves lying unattached on unconsolidated substrate.
EP: epifaunal
On a range of substrates; including sediment; consolidated substrates
including biogenic substrates (e.g. coral), and macroalgal and seagrass
substrates.
SI: semi-infaunal (Stanley, 1972)
IS: infaunal siphonate
IA: infaunal asiphonate
Absence of siphons is a major adaptive constraint in burrowing taxa
(see Stanley 1986).
WN: nestler on or within hard substrates
Excluding active borers (below).
WB: borer, nestling in hard substrate
WU: nestler within burrow of another organism in unconsolidated
substrate
Chiefly the commensal Galeommatoidea.
Feeding type
SU: suspension feeder
DU: subsurface deposit feeder
DS: surface deposit feeder
Surface and subsurface deposit feeders food sources and strategies
have been compared and contrasted by Jumars et al., (1990). Suspension
feeders may ingest deposited material and surface deposit feeders may suck
in material from the water column (Kamermans 1994). Despite this, the two
groups reflect distinct feeding strategies with often very different food
sources. There is growing evidence that some tellinid species, among surface
deposit feeders, may facultatively suspension feed. This swop between suspension
and deposit feeding may occur as a response to food quality and quantity,
hydrodynamics and predation pressure. Nevertheless, this ability may vary
between congeners (Levinton 1991). To help resolve ecological patterns,
for the present I have simply coded all tellinoids as surface deposit feeders
except those taxa which have been examined and are only known to suspension
feed.
DC: chemosymbiotic deposit feeder
CAR: microcarnivore
Mobility
IM: immobile
Includes cemented, boring, nestling and reclining taxa with no means
of repositioning, apart from that which may result from growth.
SE: sedentary
Sluggish forms which have at least some capacity to reposition in response
to disturbance.
MA: actively mobile
Including active crawlers and burrowers.
SW: swimming
Those which have the ability to swim and which are believed to do so
not solely as an escape response.
Shell fixation
UN: unattached
BA: bysally attached
CE: cemented
Including those by the shell or by byssal cementation.
Gastropod feeding categories
In general, the functional morphology of gastropod shells is much more
complicated and poorly understood than that of bivalves. Many gastropods
have lifestyles in which their shell is less intimately associated with
the substrate in or upon which it lives than the valves of an infaunal
bivalve; even in actively burrowing forms there exists a wide range of
morphologies. Consequently, I have limited our analyses of gastropods to
the one feature which I believe can be most easily and reliably assessed:
their diets. Although this may be undecipherable from their shell morphology,
broad dietary habits of closely related taxa are usually very similar and
permit confident assessment of extinct forms. For some easily studied families
diets are well known, but for many widespread and common taxa, especially
carnivores, we still know surprisingly little. In these cases, for example
the whelk family (Buccinidae), I have been forced to extrapolate data for
a few species of a genus or two to the whole family.
I have adapted the theoretical and more practical trophic classifications
of Hughes (1980) and Taylor and Reid (1984). I have made modifications
to allow a fairly precise yet practical distinction between diets. Although
it stresses clear ecological differences, it also tries to link those dietary
and feeding modes which are known to commonly vary within and between species
of a genus, particularly bearing in mind our very patchy knowledge. The
trophic classification is the following:
CP: predatory carnivores
Predators feeding on and killing whole sedentary and mobile macro-organisms
and also selective ingesters of foraminifera (foraminiferivores). Included
here are scavengers, which with just a few known exceptions, are also predators,
shifting facultatively when carrion is present (Britton & Morton 1994).
CB: browsing canivores
Predators which feed on sedentary, and typically clonal, animals (e.g.
corals and other cnidarians, sponges, ascidians) without killing them.This
also includes those ‘parasites’, which are ectoparasitic upon mostly relatively
larger sedentary or mobile prey. For our purposes, I believe there is no
useful distinction between these categories, given the varying host specificities
of parasites (e.g. within eulimids, epitoniids and pyramidellids); and
a seemingly complete gradation in relative sizes of parasite and host.
HO: herbivorous omnivores
Browsing macroherbivores with unselective omnivory, typically of epifauna
attached to macroalgae.
HM: herbivores on fine-grained substrates
Microalgivores, detritivores, microphages and unselective deposit feeder.
Also included here is a miscellany of herbivorous non-HR and HP categories,
including those living on wood or mangrove substrates.
HR: herbivores on rock, rubble or coral substrates
Microalgivores
HP: herbivores on plant or algal substrates
Micro-and macroalgivores and detritivores on macroalgal and seagrass
substrates.
SU: suspension feeders
Includes taxa feeding solely or dominantly upon suspended particles,
including mucociliary feeders.
References
BRITTON, J. C. and MORTON, B. 1994. Marine carrion and scavengers.
Oceanography and Marine Biology. An Annual Review, 32: 369-434.
HUGHES, R. N. 1980. Optimal foraging theory in the marine context.
Oceanography and Marine Biology. An Annual Review, 1980, 18: 423-481.
JUMARS, P. A., MAYER, L. M., DEMING, J. W., BAROSS, J. A. and
WHEATCROFT,
R. A. 1990. Deep-sea deposit-feeding strategies suggested by environmental
and feeding constraints. Philosophical Transactions of the Royal Society
of London, Series A, Mathematical and Physical Sciences, 331: 85-101.
KAMERMANS, P. 1994. Similarity in food source and timing of feeding
in deposit- and suspension-feeding bivalves. Marine Ecology Progress Series,
104: 63-75.
LEVINTON, J. S. 1991. Variable feeding behavior in three species
of Macoma (Bivalvia: Tellinacea) as a response to water flow and
sediment transport. Marine Biology, 110: 375-383.
STANLEY, S. M. 1970. Relation of shell form to life habits of
the Bivalvia (Mollusca). Geological Society of America Bulletin, 125, xiii,
296 pp.
______________. 1986. Population size, extinction, and speciation: the
fission effect in Neogene Bivalvia. Paleobiology, 12: 89-110.
TAYLOR, J. D. and REID, D. G. 1984. The abundance and
trophic classification of molluscs upon coral reefs in the Sudanese Red
Sea. Journal of Natural History, 18: 175-209.
