Abundance, diversity, community structure and mobility of moths in farmland.
Changes in macro-moth populations related to habitat creation were monitored using
light-traps between 1993 and 1995 on low-lying, previously intensively managed, arable
land at College Farm, Long Wittenham, Oxfordshire (grid reference SU 554 939).
Research measured the effects of the establishment of set-aside and agro-forestry in
farmland on macro-moth abundance, diversity, guild and seral structure. College Farm
data from the newly created habitats were compared with unchanging and established
ones within the Farm, a nearby Garden (500 metres away at Long Wittenham) sampled
concurrently, and data from other farmland, gardens and woodland sites. Mobility was
measured within College Farm and between it and the Garden at Long Wittenham.
Large numbers of moths, of a comparatively small number of ubiquitous species, were
found within College Farm. Abundance, which can be as high as in woodlands, indicated
that the farmland environment is less hostile to moths than has been previously thought.
Analyses showed rapid and large increases of abundance in the newly created habitats on
College Farm related to the establishment of a more diverse and architecturally more
complex ground flora. The differences in abundance between the Farm and Garden,
where moths were generally more numerous but which were sampled with more effective
light traps, progressively decreased throughout the research period. Changes 10
abundance were less marked in the Garden in line with regional population changes.
Species richness was low on College Farm in comparison to woodlands and gardens.
Within the Farm it was highest along a linear drainage Ditch but increased rapidly in a
tree Plantation in association with greater diversity of the ground flora. Species richness
was found to be constant between years in the Garden. Both the Farm and Garden and
other sites investigated in Oxfordshire and elsewhere in Britain exhibited constant species
proportions within the larger families, sub-families and genera. Alpha diversity was
constant for the Farm as a whole and for the Garden (and did not increase after the first
field season at either site) but was found to increase significantly in a tree Plantation in
the second year after its establishment. Removal of vagrant species and individuals from
analyses of the Farm and Garden totals showed that alpha diversity increased for the
Farm (but not the Garden) between 1993 and 1995. Diversity, dominance, evenness and
dissimilarity measures showed distinct habitat differences on the Farm and that the tree
Plantation improved to a similar state to that of the permanent Ditch in its second year.
These improvements were not associated with the presence of trees but were related to
increased herb diversity and complexity. Intensive management in the Plantation in 1995
resulted in reductions in diversity.
Analyses of guild structure showed that herb feeding individuals were most abundant in a
tree Plantation, associated with the ground flora, and that grass feeders dominated the
catches in a Barley-field, along a drainage Ditch and in a field of Set-aside. There were
some marked changes between years with grass feeders contributing greater numbers to
all habitat totals, being greatest in 1995. Abundance changed asynchronously and
disproportionally for herb, grass and polyphagous guilds on the Farm in comparison to
the changes in the Garden indicating that habitat creation was the cause. The proportions
of herb, grass, woody-plant, polyphagous and other moth species were found to be
constant on the Farm and in the Garden and in all other habitats investigated. Species
represented by fewer than 10 individuals on the Farm and fewer than 100 individuals in the Garden were found to comprise the vagrant fraction of their, respective, totals. The
majority of woody-plant feeding species and the guild 'others' were contained within this
fraction. There was no evidence for an increase in abundance or species richness of
woody-plant feeders as a consequence of tree planting on the Farm.
The majority of individuals on the Farm and in the Garden were representatives from
early seral communities. Almost all others were contained within the vagrant fraction of
the faunas in these sites. Abundance changed asynchronously and disproportionally for
early seres on the Farm in comparison to the changes in the Garden indicating that habitat
creation was the cause. Species proportions within all seres were found to be constant on
the Farm, in the Garden and in other habitats investigated.
Mark-release-recapture studies showed that certain species arc highly mobile in farmland,
others are comparatively poorly mobile, and that patterns of mobility change (mobility
between Farm habitats increased each year for some species) in association with habitat
creation. Moths increasingly remained within the Farm as evidenced by progressive
increases in recapture proportions there, progressive decreases in recaptures of Farm
marked moths in the Garden, and increasing proportions of multiple recaptures.